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Linux/kernel/futex.c

  1 /*
  2  *  Fast Userspace Mutexes (which I call "Futexes!").
  3  *  (C) Rusty Russell, IBM 2002
  4  *
  5  *  Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
  6  *  (C) Copyright 2003 Red Hat Inc, All Rights Reserved
  7  *
  8  *  Removed page pinning, fix privately mapped COW pages and other cleanups
  9  *  (C) Copyright 2003, 2004 Jamie Lokier
 10  *
 11  *  Robust futex support started by Ingo Molnar
 12  *  (C) Copyright 2006 Red Hat Inc, All Rights Reserved
 13  *  Thanks to Thomas Gleixner for suggestions, analysis and fixes.
 14  *
 15  *  PI-futex support started by Ingo Molnar and Thomas Gleixner
 16  *  Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 17  *  Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
 18  *
 19  *  PRIVATE futexes by Eric Dumazet
 20  *  Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
 21  *
 22  *  Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
 23  *  Copyright (C) IBM Corporation, 2009
 24  *  Thanks to Thomas Gleixner for conceptual design and careful reviews.
 25  *
 26  *  Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
 27  *  enough at me, Linus for the original (flawed) idea, Matthew
 28  *  Kirkwood for proof-of-concept implementation.
 29  *
 30  *  "The futexes are also cursed."
 31  *  "But they come in a choice of three flavours!"
 32  *
 33  *  This program is free software; you can redistribute it and/or modify
 34  *  it under the terms of the GNU General Public License as published by
 35  *  the Free Software Foundation; either version 2 of the License, or
 36  *  (at your option) any later version.
 37  *
 38  *  This program is distributed in the hope that it will be useful,
 39  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 40  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 41  *  GNU General Public License for more details.
 42  *
 43  *  You should have received a copy of the GNU General Public License
 44  *  along with this program; if not, write to the Free Software
 45  *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 46  */
 47 #include <linux/slab.h>
 48 #include <linux/poll.h>
 49 #include <linux/fs.h>
 50 #include <linux/file.h>
 51 #include <linux/jhash.h>
 52 #include <linux/init.h>
 53 #include <linux/futex.h>
 54 #include <linux/mount.h>
 55 #include <linux/pagemap.h>
 56 #include <linux/syscalls.h>
 57 #include <linux/signal.h>
 58 #include <linux/export.h>
 59 #include <linux/magic.h>
 60 #include <linux/pid.h>
 61 #include <linux/nsproxy.h>
 62 #include <linux/ptrace.h>
 63 #include <linux/sched/rt.h>
 64 #include <linux/hugetlb.h>
 65 #include <linux/freezer.h>
 66 #include <linux/bootmem.h>
 67 #include <linux/fault-inject.h>
 68 
 69 #include <asm/futex.h>
 70 
 71 #include "locking/rtmutex_common.h"
 72 
 73 /*
 74  * READ this before attempting to hack on futexes!
 75  *
 76  * Basic futex operation and ordering guarantees
 77  * =============================================
 78  *
 79  * The waiter reads the futex value in user space and calls
 80  * futex_wait(). This function computes the hash bucket and acquires
 81  * the hash bucket lock. After that it reads the futex user space value
 82  * again and verifies that the data has not changed. If it has not changed
 83  * it enqueues itself into the hash bucket, releases the hash bucket lock
 84  * and schedules.
 85  *
 86  * The waker side modifies the user space value of the futex and calls
 87  * futex_wake(). This function computes the hash bucket and acquires the
 88  * hash bucket lock. Then it looks for waiters on that futex in the hash
 89  * bucket and wakes them.
 90  *
 91  * In futex wake up scenarios where no tasks are blocked on a futex, taking
 92  * the hb spinlock can be avoided and simply return. In order for this
 93  * optimization to work, ordering guarantees must exist so that the waiter
 94  * being added to the list is acknowledged when the list is concurrently being
 95  * checked by the waker, avoiding scenarios like the following:
 96  *
 97  * CPU 0                               CPU 1
 98  * val = *futex;
 99  * sys_futex(WAIT, futex, val);
100  *   futex_wait(futex, val);
101  *   uval = *futex;
102  *                                     *futex = newval;
103  *                                     sys_futex(WAKE, futex);
104  *                                       futex_wake(futex);
105  *                                       if (queue_empty())
106  *                                         return;
107  *   if (uval == val)
108  *      lock(hash_bucket(futex));
109  *      queue();
110  *     unlock(hash_bucket(futex));
111  *     schedule();
112  *
113  * This would cause the waiter on CPU 0 to wait forever because it
114  * missed the transition of the user space value from val to newval
115  * and the waker did not find the waiter in the hash bucket queue.
116  *
117  * The correct serialization ensures that a waiter either observes
118  * the changed user space value before blocking or is woken by a
119  * concurrent waker:
120  *
121  * CPU 0                                 CPU 1
122  * val = *futex;
123  * sys_futex(WAIT, futex, val);
124  *   futex_wait(futex, val);
125  *
126  *   waiters++; (a)
127  *   smp_mb(); (A) <-- paired with -.
128  *                                  |
129  *   lock(hash_bucket(futex));      |
130  *                                  |
131  *   uval = *futex;                 |
132  *                                  |        *futex = newval;
133  *                                  |        sys_futex(WAKE, futex);
134  *                                  |          futex_wake(futex);
135  *                                  |
136  *                                  `--------> smp_mb(); (B)
137  *   if (uval == val)
138  *     queue();
139  *     unlock(hash_bucket(futex));
140  *     schedule();                         if (waiters)
141  *                                           lock(hash_bucket(futex));
142  *   else                                    wake_waiters(futex);
143  *     waiters--; (b)                        unlock(hash_bucket(futex));
144  *
145  * Where (A) orders the waiters increment and the futex value read through
146  * atomic operations (see hb_waiters_inc) and where (B) orders the write
147  * to futex and the waiters read -- this is done by the barriers for both
148  * shared and private futexes in get_futex_key_refs().
149  *
150  * This yields the following case (where X:=waiters, Y:=futex):
151  *
152  *      X = Y = 0
153  *
154  *      w[X]=1          w[Y]=1
155  *      MB              MB
156  *      r[Y]=y          r[X]=x
157  *
158  * Which guarantees that x==0 && y==0 is impossible; which translates back into
159  * the guarantee that we cannot both miss the futex variable change and the
160  * enqueue.
161  *
162  * Note that a new waiter is accounted for in (a) even when it is possible that
163  * the wait call can return error, in which case we backtrack from it in (b).
164  * Refer to the comment in queue_lock().
165  *
166  * Similarly, in order to account for waiters being requeued on another
167  * address we always increment the waiters for the destination bucket before
168  * acquiring the lock. It then decrements them again  after releasing it -
169  * the code that actually moves the futex(es) between hash buckets (requeue_futex)
170  * will do the additional required waiter count housekeeping. This is done for
171  * double_lock_hb() and double_unlock_hb(), respectively.
172  */
173 
174 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
175 int __read_mostly futex_cmpxchg_enabled;
176 #endif
177 
178 /*
179  * Futex flags used to encode options to functions and preserve them across
180  * restarts.
181  */
182 #define FLAGS_SHARED            0x01
183 #define FLAGS_CLOCKRT           0x02
184 #define FLAGS_HAS_TIMEOUT       0x04
185 
186 /*
187  * Priority Inheritance state:
188  */
189 struct futex_pi_state {
190         /*
191          * list of 'owned' pi_state instances - these have to be
192          * cleaned up in do_exit() if the task exits prematurely:
193          */
194         struct list_head list;
195 
196         /*
197          * The PI object:
198          */
199         struct rt_mutex pi_mutex;
200 
201         struct task_struct *owner;
202         atomic_t refcount;
203 
204         union futex_key key;
205 };
206 
207 /**
208  * struct futex_q - The hashed futex queue entry, one per waiting task
209  * @list:               priority-sorted list of tasks waiting on this futex
210  * @task:               the task waiting on the futex
211  * @lock_ptr:           the hash bucket lock
212  * @key:                the key the futex is hashed on
213  * @pi_state:           optional priority inheritance state
214  * @rt_waiter:          rt_waiter storage for use with requeue_pi
215  * @requeue_pi_key:     the requeue_pi target futex key
216  * @bitset:             bitset for the optional bitmasked wakeup
217  *
218  * We use this hashed waitqueue, instead of a normal wait_queue_t, so
219  * we can wake only the relevant ones (hashed queues may be shared).
220  *
221  * A futex_q has a woken state, just like tasks have TASK_RUNNING.
222  * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
223  * The order of wakeup is always to make the first condition true, then
224  * the second.
225  *
226  * PI futexes are typically woken before they are removed from the hash list via
227  * the rt_mutex code. See unqueue_me_pi().
228  */
229 struct futex_q {
230         struct plist_node list;
231 
232         struct task_struct *task;
233         spinlock_t *lock_ptr;
234         union futex_key key;
235         struct futex_pi_state *pi_state;
236         struct rt_mutex_waiter *rt_waiter;
237         union futex_key *requeue_pi_key;
238         u32 bitset;
239 };
240 
241 static const struct futex_q futex_q_init = {
242         /* list gets initialized in queue_me()*/
243         .key = FUTEX_KEY_INIT,
244         .bitset = FUTEX_BITSET_MATCH_ANY
245 };
246 
247 /*
248  * Hash buckets are shared by all the futex_keys that hash to the same
249  * location.  Each key may have multiple futex_q structures, one for each task
250  * waiting on a futex.
251  */
252 struct futex_hash_bucket {
253         atomic_t waiters;
254         spinlock_t lock;
255         struct plist_head chain;
256 } ____cacheline_aligned_in_smp;
257 
258 /*
259  * The base of the bucket array and its size are always used together
260  * (after initialization only in hash_futex()), so ensure that they
261  * reside in the same cacheline.
262  */
263 static struct {
264         struct futex_hash_bucket *queues;
265         unsigned long            hashsize;
266 } __futex_data __read_mostly __aligned(2*sizeof(long));
267 #define futex_queues   (__futex_data.queues)
268 #define futex_hashsize (__futex_data.hashsize)
269 
270 
271 /*
272  * Fault injections for futexes.
273  */
274 #ifdef CONFIG_FAIL_FUTEX
275 
276 static struct {
277         struct fault_attr attr;
278 
279         bool ignore_private;
280 } fail_futex = {
281         .attr = FAULT_ATTR_INITIALIZER,
282         .ignore_private = false,
283 };
284 
285 static int __init setup_fail_futex(char *str)
286 {
287         return setup_fault_attr(&fail_futex.attr, str);
288 }
289 __setup("fail_futex=", setup_fail_futex);
290 
291 static bool should_fail_futex(bool fshared)
292 {
293         if (fail_futex.ignore_private && !fshared)
294                 return false;
295 
296         return should_fail(&fail_futex.attr, 1);
297 }
298 
299 #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
300 
301 static int __init fail_futex_debugfs(void)
302 {
303         umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
304         struct dentry *dir;
305 
306         dir = fault_create_debugfs_attr("fail_futex", NULL,
307                                         &fail_futex.attr);
308         if (IS_ERR(dir))
309                 return PTR_ERR(dir);
310 
311         if (!debugfs_create_bool("ignore-private", mode, dir,
312                                  &fail_futex.ignore_private)) {
313                 debugfs_remove_recursive(dir);
314                 return -ENOMEM;
315         }
316 
317         return 0;
318 }
319 
320 late_initcall(fail_futex_debugfs);
321 
322 #endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
323 
324 #else
325 static inline bool should_fail_futex(bool fshared)
326 {
327         return false;
328 }
329 #endif /* CONFIG_FAIL_FUTEX */
330 
331 static inline void futex_get_mm(union futex_key *key)
332 {
333         atomic_inc(&key->private.mm->mm_count);
334         /*
335          * Ensure futex_get_mm() implies a full barrier such that
336          * get_futex_key() implies a full barrier. This is relied upon
337          * as smp_mb(); (B), see the ordering comment above.
338          */
339         smp_mb__after_atomic();
340 }
341 
342 /*
343  * Reflects a new waiter being added to the waitqueue.
344  */
345 static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
346 {
347 #ifdef CONFIG_SMP
348         atomic_inc(&hb->waiters);
349         /*
350          * Full barrier (A), see the ordering comment above.
351          */
352         smp_mb__after_atomic();
353 #endif
354 }
355 
356 /*
357  * Reflects a waiter being removed from the waitqueue by wakeup
358  * paths.
359  */
360 static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
361 {
362 #ifdef CONFIG_SMP
363         atomic_dec(&hb->waiters);
364 #endif
365 }
366 
367 static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
368 {
369 #ifdef CONFIG_SMP
370         return atomic_read(&hb->waiters);
371 #else
372         return 1;
373 #endif
374 }
375 
376 /*
377  * We hash on the keys returned from get_futex_key (see below).
378  */
379 static struct futex_hash_bucket *hash_futex(union futex_key *key)
380 {
381         u32 hash = jhash2((u32*)&key->both.word,
382                           (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
383                           key->both.offset);
384         return &futex_queues[hash & (futex_hashsize - 1)];
385 }
386 
387 /*
388  * Return 1 if two futex_keys are equal, 0 otherwise.
389  */
390 static inline int match_futex(union futex_key *key1, union futex_key *key2)
391 {
392         return (key1 && key2
393                 && key1->both.word == key2->both.word
394                 && key1->both.ptr == key2->both.ptr
395                 && key1->both.offset == key2->both.offset);
396 }
397 
398 /*
399  * Take a reference to the resource addressed by a key.
400  * Can be called while holding spinlocks.
401  *
402  */
403 static void get_futex_key_refs(union futex_key *key)
404 {
405         if (!key->both.ptr)
406                 return;
407 
408         switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
409         case FUT_OFF_INODE:
410                 ihold(key->shared.inode); /* implies smp_mb(); (B) */
411                 break;
412         case FUT_OFF_MMSHARED:
413                 futex_get_mm(key); /* implies smp_mb(); (B) */
414                 break;
415         default:
416                 /*
417                  * Private futexes do not hold reference on an inode or
418                  * mm, therefore the only purpose of calling get_futex_key_refs
419                  * is because we need the barrier for the lockless waiter check.
420                  */
421                 smp_mb(); /* explicit smp_mb(); (B) */
422         }
423 }
424 
425 /*
426  * Drop a reference to the resource addressed by a key.
427  * The hash bucket spinlock must not be held. This is
428  * a no-op for private futexes, see comment in the get
429  * counterpart.
430  */
431 static void drop_futex_key_refs(union futex_key *key)
432 {
433         if (!key->both.ptr) {
434                 /* If we're here then we tried to put a key we failed to get */
435                 WARN_ON_ONCE(1);
436                 return;
437         }
438 
439         switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
440         case FUT_OFF_INODE:
441                 iput(key->shared.inode);
442                 break;
443         case FUT_OFF_MMSHARED:
444                 mmdrop(key->private.mm);
445                 break;
446         }
447 }
448 
449 /**
450  * get_futex_key() - Get parameters which are the keys for a futex
451  * @uaddr:      virtual address of the futex
452  * @fshared:    0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
453  * @key:        address where result is stored.
454  * @rw:         mapping needs to be read/write (values: VERIFY_READ,
455  *              VERIFY_WRITE)
456  *
457  * Return: a negative error code or 0
458  *
459  * The key words are stored in *key on success.
460  *
461  * For shared mappings, it's (page->index, file_inode(vma->vm_file),
462  * offset_within_page).  For private mappings, it's (uaddr, current->mm).
463  * We can usually work out the index without swapping in the page.
464  *
465  * lock_page() might sleep, the caller should not hold a spinlock.
466  */
467 static int
468 get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
469 {
470         unsigned long address = (unsigned long)uaddr;
471         struct mm_struct *mm = current->mm;
472         struct page *page;
473         struct address_space *mapping;
474         int err, ro = 0;
475 
476         /*
477          * The futex address must be "naturally" aligned.
478          */
479         key->both.offset = address % PAGE_SIZE;
480         if (unlikely((address % sizeof(u32)) != 0))
481                 return -EINVAL;
482         address -= key->both.offset;
483 
484         if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
485                 return -EFAULT;
486 
487         if (unlikely(should_fail_futex(fshared)))
488                 return -EFAULT;
489 
490         /*
491          * PROCESS_PRIVATE futexes are fast.
492          * As the mm cannot disappear under us and the 'key' only needs
493          * virtual address, we dont even have to find the underlying vma.
494          * Note : We do have to check 'uaddr' is a valid user address,
495          *        but access_ok() should be faster than find_vma()
496          */
497         if (!fshared) {
498                 key->private.mm = mm;
499                 key->private.address = address;
500                 get_futex_key_refs(key);  /* implies smp_mb(); (B) */
501                 return 0;
502         }
503 
504 again:
505         /* Ignore any VERIFY_READ mapping (futex common case) */
506         if (unlikely(should_fail_futex(fshared)))
507                 return -EFAULT;
508 
509         err = get_user_pages_fast(address, 1, 1, &page);
510         /*
511          * If write access is not required (eg. FUTEX_WAIT), try
512          * and get read-only access.
513          */
514         if (err == -EFAULT && rw == VERIFY_READ) {
515                 err = get_user_pages_fast(address, 1, 0, &page);
516                 ro = 1;
517         }
518         if (err < 0)
519                 return err;
520         else
521                 err = 0;
522 
523         /*
524          * The treatment of mapping from this point on is critical. The page
525          * lock protects many things but in this context the page lock
526          * stabilizes mapping, prevents inode freeing in the shared
527          * file-backed region case and guards against movement to swap cache.
528          *
529          * Strictly speaking the page lock is not needed in all cases being
530          * considered here and page lock forces unnecessarily serialization
531          * From this point on, mapping will be re-verified if necessary and
532          * page lock will be acquired only if it is unavoidable
533          */
534         page = compound_head(page);
535         mapping = READ_ONCE(page->mapping);
536 
537         /*
538          * If page->mapping is NULL, then it cannot be a PageAnon
539          * page; but it might be the ZERO_PAGE or in the gate area or
540          * in a special mapping (all cases which we are happy to fail);
541          * or it may have been a good file page when get_user_pages_fast
542          * found it, but truncated or holepunched or subjected to
543          * invalidate_complete_page2 before we got the page lock (also
544          * cases which we are happy to fail).  And we hold a reference,
545          * so refcount care in invalidate_complete_page's remove_mapping
546          * prevents drop_caches from setting mapping to NULL beneath us.
547          *
548          * The case we do have to guard against is when memory pressure made
549          * shmem_writepage move it from filecache to swapcache beneath us:
550          * an unlikely race, but we do need to retry for page->mapping.
551          */
552         if (unlikely(!mapping)) {
553                 int shmem_swizzled;
554 
555                 /*
556                  * Page lock is required to identify which special case above
557                  * applies. If this is really a shmem page then the page lock
558                  * will prevent unexpected transitions.
559                  */
560                 lock_page(page);
561                 shmem_swizzled = PageSwapCache(page) || page->mapping;
562                 unlock_page(page);
563                 put_page(page);
564 
565                 if (shmem_swizzled)
566                         goto again;
567 
568                 return -EFAULT;
569         }
570 
571         /*
572          * Private mappings are handled in a simple way.
573          *
574          * If the futex key is stored on an anonymous page, then the associated
575          * object is the mm which is implicitly pinned by the calling process.
576          *
577          * NOTE: When userspace waits on a MAP_SHARED mapping, even if
578          * it's a read-only handle, it's expected that futexes attach to
579          * the object not the particular process.
580          */
581         if (PageAnon(page)) {
582                 /*
583                  * A RO anonymous page will never change and thus doesn't make
584                  * sense for futex operations.
585                  */
586                 if (unlikely(should_fail_futex(fshared)) || ro) {
587                         err = -EFAULT;
588                         goto out;
589                 }
590 
591                 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
592                 key->private.mm = mm;
593                 key->private.address = address;
594 
595                 get_futex_key_refs(key); /* implies smp_mb(); (B) */
596 
597         } else {
598                 struct inode *inode;
599 
600                 /*
601                  * The associated futex object in this case is the inode and
602                  * the page->mapping must be traversed. Ordinarily this should
603                  * be stabilised under page lock but it's not strictly
604                  * necessary in this case as we just want to pin the inode, not
605                  * update the radix tree or anything like that.
606                  *
607                  * The RCU read lock is taken as the inode is finally freed
608                  * under RCU. If the mapping still matches expectations then the
609                  * mapping->host can be safely accessed as being a valid inode.
610                  */
611                 rcu_read_lock();
612 
613                 if (READ_ONCE(page->mapping) != mapping) {
614                         rcu_read_unlock();
615                         put_page(page);
616 
617                         goto again;
618                 }
619 
620                 inode = READ_ONCE(mapping->host);
621                 if (!inode) {
622                         rcu_read_unlock();
623                         put_page(page);
624 
625                         goto again;
626                 }
627 
628                 /*
629                  * Take a reference unless it is about to be freed. Previously
630                  * this reference was taken by ihold under the page lock
631                  * pinning the inode in place so i_lock was unnecessary. The
632                  * only way for this check to fail is if the inode was
633                  * truncated in parallel so warn for now if this happens.
634                  *
635                  * We are not calling into get_futex_key_refs() in file-backed
636                  * cases, therefore a successful atomic_inc return below will
637                  * guarantee that get_futex_key() will still imply smp_mb(); (B).
638                  */
639                 if (WARN_ON_ONCE(!atomic_inc_not_zero(&inode->i_count))) {
640                         rcu_read_unlock();
641                         put_page(page);
642 
643                         goto again;
644                 }
645 
646                 /* Should be impossible but lets be paranoid for now */
647                 if (WARN_ON_ONCE(inode->i_mapping != mapping)) {
648                         err = -EFAULT;
649                         rcu_read_unlock();
650                         iput(inode);
651 
652                         goto out;
653                 }
654 
655                 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
656                 key->shared.inode = inode;
657                 key->shared.pgoff = basepage_index(page);
658                 rcu_read_unlock();
659         }
660 
661 out:
662         put_page(page);
663         return err;
664 }
665 
666 static inline void put_futex_key(union futex_key *key)
667 {
668         drop_futex_key_refs(key);
669 }
670 
671 /**
672  * fault_in_user_writeable() - Fault in user address and verify RW access
673  * @uaddr:      pointer to faulting user space address
674  *
675  * Slow path to fixup the fault we just took in the atomic write
676  * access to @uaddr.
677  *
678  * We have no generic implementation of a non-destructive write to the
679  * user address. We know that we faulted in the atomic pagefault
680  * disabled section so we can as well avoid the #PF overhead by
681  * calling get_user_pages() right away.
682  */
683 static int fault_in_user_writeable(u32 __user *uaddr)
684 {
685         struct mm_struct *mm = current->mm;
686         int ret;
687 
688         down_read(&mm->mmap_sem);
689         ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
690                                FAULT_FLAG_WRITE, NULL);
691         up_read(&mm->mmap_sem);
692 
693         return ret < 0 ? ret : 0;
694 }
695 
696 /**
697  * futex_top_waiter() - Return the highest priority waiter on a futex
698  * @hb:         the hash bucket the futex_q's reside in
699  * @key:        the futex key (to distinguish it from other futex futex_q's)
700  *
701  * Must be called with the hb lock held.
702  */
703 static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
704                                         union futex_key *key)
705 {
706         struct futex_q *this;
707 
708         plist_for_each_entry(this, &hb->chain, list) {
709                 if (match_futex(&this->key, key))
710                         return this;
711         }
712         return NULL;
713 }
714 
715 static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
716                                       u32 uval, u32 newval)
717 {
718         int ret;
719 
720         pagefault_disable();
721         ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
722         pagefault_enable();
723 
724         return ret;
725 }
726 
727 static int get_futex_value_locked(u32 *dest, u32 __user *from)
728 {
729         int ret;
730 
731         pagefault_disable();
732         ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
733         pagefault_enable();
734 
735         return ret ? -EFAULT : 0;
736 }
737 
738 
739 /*
740  * PI code:
741  */
742 static int refill_pi_state_cache(void)
743 {
744         struct futex_pi_state *pi_state;
745 
746         if (likely(current->pi_state_cache))
747                 return 0;
748 
749         pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
750 
751         if (!pi_state)
752                 return -ENOMEM;
753 
754         INIT_LIST_HEAD(&pi_state->list);
755         /* pi_mutex gets initialized later */
756         pi_state->owner = NULL;
757         atomic_set(&pi_state->refcount, 1);
758         pi_state->key = FUTEX_KEY_INIT;
759 
760         current->pi_state_cache = pi_state;
761 
762         return 0;
763 }
764 
765 static struct futex_pi_state * alloc_pi_state(void)
766 {
767         struct futex_pi_state *pi_state = current->pi_state_cache;
768 
769         WARN_ON(!pi_state);
770         current->pi_state_cache = NULL;
771 
772         return pi_state;
773 }
774 
775 /*
776  * Drops a reference to the pi_state object and frees or caches it
777  * when the last reference is gone.
778  *
779  * Must be called with the hb lock held.
780  */
781 static void put_pi_state(struct futex_pi_state *pi_state)
782 {
783         if (!pi_state)
784                 return;
785 
786         if (!atomic_dec_and_test(&pi_state->refcount))
787                 return;
788 
789         /*
790          * If pi_state->owner is NULL, the owner is most probably dying
791          * and has cleaned up the pi_state already
792          */
793         if (pi_state->owner) {
794                 raw_spin_lock_irq(&pi_state->owner->pi_lock);
795                 list_del_init(&pi_state->list);
796                 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
797 
798                 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
799         }
800 
801         if (current->pi_state_cache)
802                 kfree(pi_state);
803         else {
804                 /*
805                  * pi_state->list is already empty.
806                  * clear pi_state->owner.
807                  * refcount is at 0 - put it back to 1.
808                  */
809                 pi_state->owner = NULL;
810                 atomic_set(&pi_state->refcount, 1);
811                 current->pi_state_cache = pi_state;
812         }
813 }
814 
815 /*
816  * Look up the task based on what TID userspace gave us.
817  * We dont trust it.
818  */
819 static struct task_struct * futex_find_get_task(pid_t pid)
820 {
821         struct task_struct *p;
822 
823         rcu_read_lock();
824         p = find_task_by_vpid(pid);
825         if (p)
826                 get_task_struct(p);
827 
828         rcu_read_unlock();
829 
830         return p;
831 }
832 
833 /*
834  * This task is holding PI mutexes at exit time => bad.
835  * Kernel cleans up PI-state, but userspace is likely hosed.
836  * (Robust-futex cleanup is separate and might save the day for userspace.)
837  */
838 void exit_pi_state_list(struct task_struct *curr)
839 {
840         struct list_head *next, *head = &curr->pi_state_list;
841         struct futex_pi_state *pi_state;
842         struct futex_hash_bucket *hb;
843         union futex_key key = FUTEX_KEY_INIT;
844 
845         if (!futex_cmpxchg_enabled)
846                 return;
847         /*
848          * We are a ZOMBIE and nobody can enqueue itself on
849          * pi_state_list anymore, but we have to be careful
850          * versus waiters unqueueing themselves:
851          */
852         raw_spin_lock_irq(&curr->pi_lock);
853         while (!list_empty(head)) {
854 
855                 next = head->next;
856                 pi_state = list_entry(next, struct futex_pi_state, list);
857                 key = pi_state->key;
858                 hb = hash_futex(&key);
859                 raw_spin_unlock_irq(&curr->pi_lock);
860 
861                 spin_lock(&hb->lock);
862 
863                 raw_spin_lock_irq(&curr->pi_lock);
864                 /*
865                  * We dropped the pi-lock, so re-check whether this
866                  * task still owns the PI-state:
867                  */
868                 if (head->next != next) {
869                         spin_unlock(&hb->lock);
870                         continue;
871                 }
872 
873                 WARN_ON(pi_state->owner != curr);
874                 WARN_ON(list_empty(&pi_state->list));
875                 list_del_init(&pi_state->list);
876                 pi_state->owner = NULL;
877                 raw_spin_unlock_irq(&curr->pi_lock);
878 
879                 rt_mutex_unlock(&pi_state->pi_mutex);
880 
881                 spin_unlock(&hb->lock);
882 
883                 raw_spin_lock_irq(&curr->pi_lock);
884         }
885         raw_spin_unlock_irq(&curr->pi_lock);
886 }
887 
888 /*
889  * We need to check the following states:
890  *
891  *      Waiter | pi_state | pi->owner | uTID      | uODIED | ?
892  *
893  * [1]  NULL   | ---      | ---       | 0         | 0/1    | Valid
894  * [2]  NULL   | ---      | ---       | >0        | 0/1    | Valid
895  *
896  * [3]  Found  | NULL     | --        | Any       | 0/1    | Invalid
897  *
898  * [4]  Found  | Found    | NULL      | 0         | 1      | Valid
899  * [5]  Found  | Found    | NULL      | >0        | 1      | Invalid
900  *
901  * [6]  Found  | Found    | task      | 0         | 1      | Valid
902  *
903  * [7]  Found  | Found    | NULL      | Any       | 0      | Invalid
904  *
905  * [8]  Found  | Found    | task      | ==taskTID | 0/1    | Valid
906  * [9]  Found  | Found    | task      | 0         | 0      | Invalid
907  * [10] Found  | Found    | task      | !=taskTID | 0/1    | Invalid
908  *
909  * [1]  Indicates that the kernel can acquire the futex atomically. We
910  *      came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
911  *
912  * [2]  Valid, if TID does not belong to a kernel thread. If no matching
913  *      thread is found then it indicates that the owner TID has died.
914  *
915  * [3]  Invalid. The waiter is queued on a non PI futex
916  *
917  * [4]  Valid state after exit_robust_list(), which sets the user space
918  *      value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
919  *
920  * [5]  The user space value got manipulated between exit_robust_list()
921  *      and exit_pi_state_list()
922  *
923  * [6]  Valid state after exit_pi_state_list() which sets the new owner in
924  *      the pi_state but cannot access the user space value.
925  *
926  * [7]  pi_state->owner can only be NULL when the OWNER_DIED bit is set.
927  *
928  * [8]  Owner and user space value match
929  *
930  * [9]  There is no transient state which sets the user space TID to 0
931  *      except exit_robust_list(), but this is indicated by the
932  *      FUTEX_OWNER_DIED bit. See [4]
933  *
934  * [10] There is no transient state which leaves owner and user space
935  *      TID out of sync.
936  */
937 
938 /*
939  * Validate that the existing waiter has a pi_state and sanity check
940  * the pi_state against the user space value. If correct, attach to
941  * it.
942  */
943 static int attach_to_pi_state(u32 uval, struct futex_pi_state *pi_state,
944                               struct futex_pi_state **ps)
945 {
946         pid_t pid = uval & FUTEX_TID_MASK;
947 
948         /*
949          * Userspace might have messed up non-PI and PI futexes [3]
950          */
951         if (unlikely(!pi_state))
952                 return -EINVAL;
953 
954         WARN_ON(!atomic_read(&pi_state->refcount));
955 
956         /*
957          * Handle the owner died case:
958          */
959         if (uval & FUTEX_OWNER_DIED) {
960                 /*
961                  * exit_pi_state_list sets owner to NULL and wakes the
962                  * topmost waiter. The task which acquires the
963                  * pi_state->rt_mutex will fixup owner.
964                  */
965                 if (!pi_state->owner) {
966                         /*
967                          * No pi state owner, but the user space TID
968                          * is not 0. Inconsistent state. [5]
969                          */
970                         if (pid)
971                                 return -EINVAL;
972                         /*
973                          * Take a ref on the state and return success. [4]
974                          */
975                         goto out_state;
976                 }
977 
978                 /*
979                  * If TID is 0, then either the dying owner has not
980                  * yet executed exit_pi_state_list() or some waiter
981                  * acquired the rtmutex in the pi state, but did not
982                  * yet fixup the TID in user space.
983                  *
984                  * Take a ref on the state and return success. [6]
985                  */
986                 if (!pid)
987                         goto out_state;
988         } else {
989                 /*
990                  * If the owner died bit is not set, then the pi_state
991                  * must have an owner. [7]
992                  */
993                 if (!pi_state->owner)
994                         return -EINVAL;
995         }
996 
997         /*
998          * Bail out if user space manipulated the futex value. If pi
999          * state exists then the owner TID must be the same as the
1000          * user space TID. [9/10]
1001          */
1002         if (pid != task_pid_vnr(pi_state->owner))
1003                 return -EINVAL;
1004 out_state:
1005         atomic_inc(&pi_state->refcount);
1006         *ps = pi_state;
1007         return 0;
1008 }
1009 
1010 /*
1011  * Lookup the task for the TID provided from user space and attach to
1012  * it after doing proper sanity checks.
1013  */
1014 static int attach_to_pi_owner(u32 uval, union futex_key *key,
1015                               struct futex_pi_state **ps)
1016 {
1017         pid_t pid = uval & FUTEX_TID_MASK;
1018         struct futex_pi_state *pi_state;
1019         struct task_struct *p;
1020 
1021         /*
1022          * We are the first waiter - try to look up the real owner and attach
1023          * the new pi_state to it, but bail out when TID = 0 [1]
1024          */
1025         if (!pid)
1026                 return -ESRCH;
1027         p = futex_find_get_task(pid);
1028         if (!p)
1029                 return -ESRCH;
1030 
1031         if (unlikely(p->flags & PF_KTHREAD)) {
1032                 put_task_struct(p);
1033                 return -EPERM;
1034         }
1035 
1036         /*
1037          * We need to look at the task state flags to figure out,
1038          * whether the task is exiting. To protect against the do_exit
1039          * change of the task flags, we do this protected by
1040          * p->pi_lock:
1041          */
1042         raw_spin_lock_irq(&p->pi_lock);
1043         if (unlikely(p->flags & PF_EXITING)) {
1044                 /*
1045                  * The task is on the way out. When PF_EXITPIDONE is
1046                  * set, we know that the task has finished the
1047                  * cleanup:
1048                  */
1049                 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
1050 
1051                 raw_spin_unlock_irq(&p->pi_lock);
1052                 put_task_struct(p);
1053                 return ret;
1054         }
1055 
1056         /*
1057          * No existing pi state. First waiter. [2]
1058          */
1059         pi_state = alloc_pi_state();
1060 
1061         /*
1062          * Initialize the pi_mutex in locked state and make @p
1063          * the owner of it:
1064          */
1065         rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
1066 
1067         /* Store the key for possible exit cleanups: */
1068         pi_state->key = *key;
1069 
1070         WARN_ON(!list_empty(&pi_state->list));
1071         list_add(&pi_state->list, &p->pi_state_list);
1072         pi_state->owner = p;
1073         raw_spin_unlock_irq(&p->pi_lock);
1074 
1075         put_task_struct(p);
1076 
1077         *ps = pi_state;
1078 
1079         return 0;
1080 }
1081 
1082 static int lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
1083                            union futex_key *key, struct futex_pi_state **ps)
1084 {
1085         struct futex_q *match = futex_top_waiter(hb, key);
1086 
1087         /*
1088          * If there is a waiter on that futex, validate it and
1089          * attach to the pi_state when the validation succeeds.
1090          */
1091         if (match)
1092                 return attach_to_pi_state(uval, match->pi_state, ps);
1093 
1094         /*
1095          * We are the first waiter - try to look up the owner based on
1096          * @uval and attach to it.
1097          */
1098         return attach_to_pi_owner(uval, key, ps);
1099 }
1100 
1101 static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
1102 {
1103         u32 uninitialized_var(curval);
1104 
1105         if (unlikely(should_fail_futex(true)))
1106                 return -EFAULT;
1107 
1108         if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
1109                 return -EFAULT;
1110 
1111         /*If user space value changed, let the caller retry */
1112         return curval != uval ? -EAGAIN : 0;
1113 }
1114 
1115 /**
1116  * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
1117  * @uaddr:              the pi futex user address
1118  * @hb:                 the pi futex hash bucket
1119  * @key:                the futex key associated with uaddr and hb
1120  * @ps:                 the pi_state pointer where we store the result of the
1121  *                      lookup
1122  * @task:               the task to perform the atomic lock work for.  This will
1123  *                      be "current" except in the case of requeue pi.
1124  * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
1125  *
1126  * Return:
1127  *  0 - ready to wait;
1128  *  1 - acquired the lock;
1129  * <0 - error
1130  *
1131  * The hb->lock and futex_key refs shall be held by the caller.
1132  */
1133 static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
1134                                 union futex_key *key,
1135                                 struct futex_pi_state **ps,
1136                                 struct task_struct *task, int set_waiters)
1137 {
1138         u32 uval, newval, vpid = task_pid_vnr(task);
1139         struct futex_q *match;
1140         int ret;
1141 
1142         /*
1143          * Read the user space value first so we can validate a few
1144          * things before proceeding further.
1145          */
1146         if (get_futex_value_locked(&uval, uaddr))
1147                 return -EFAULT;
1148 
1149         if (unlikely(should_fail_futex(true)))
1150                 return -EFAULT;
1151 
1152         /*
1153          * Detect deadlocks.
1154          */
1155         if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
1156                 return -EDEADLK;
1157 
1158         if ((unlikely(should_fail_futex(true))))
1159                 return -EDEADLK;
1160 
1161         /*
1162          * Lookup existing state first. If it exists, try to attach to
1163          * its pi_state.
1164          */
1165         match = futex_top_waiter(hb, key);
1166         if (match)
1167                 return attach_to_pi_state(uval, match->pi_state, ps);
1168 
1169         /*
1170          * No waiter and user TID is 0. We are here because the
1171          * waiters or the owner died bit is set or called from
1172          * requeue_cmp_pi or for whatever reason something took the
1173          * syscall.
1174          */
1175         if (!(uval & FUTEX_TID_MASK)) {
1176                 /*
1177                  * We take over the futex. No other waiters and the user space
1178                  * TID is 0. We preserve the owner died bit.
1179                  */
1180                 newval = uval & FUTEX_OWNER_DIED;
1181                 newval |= vpid;
1182 
1183                 /* The futex requeue_pi code can enforce the waiters bit */
1184                 if (set_waiters)
1185                         newval |= FUTEX_WAITERS;
1186 
1187                 ret = lock_pi_update_atomic(uaddr, uval, newval);
1188                 /* If the take over worked, return 1 */
1189                 return ret < 0 ? ret : 1;
1190         }
1191 
1192         /*
1193          * First waiter. Set the waiters bit before attaching ourself to
1194          * the owner. If owner tries to unlock, it will be forced into
1195          * the kernel and blocked on hb->lock.
1196          */
1197         newval = uval | FUTEX_WAITERS;
1198         ret = lock_pi_update_atomic(uaddr, uval, newval);
1199         if (ret)
1200                 return ret;
1201         /*
1202          * If the update of the user space value succeeded, we try to
1203          * attach to the owner. If that fails, no harm done, we only
1204          * set the FUTEX_WAITERS bit in the user space variable.
1205          */
1206         return attach_to_pi_owner(uval, key, ps);
1207 }
1208 
1209 /**
1210  * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
1211  * @q:  The futex_q to unqueue
1212  *
1213  * The q->lock_ptr must not be NULL and must be held by the caller.
1214  */
1215 static void __unqueue_futex(struct futex_q *q)
1216 {
1217         struct futex_hash_bucket *hb;
1218 
1219         if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
1220             || WARN_ON(plist_node_empty(&q->list)))
1221                 return;
1222 
1223         hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
1224         plist_del(&q->list, &hb->chain);
1225         hb_waiters_dec(hb);
1226 }
1227 
1228 /*
1229  * The hash bucket lock must be held when this is called.
1230  * Afterwards, the futex_q must not be accessed. Callers
1231  * must ensure to later call wake_up_q() for the actual
1232  * wakeups to occur.
1233  */
1234 static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
1235 {
1236         struct task_struct *p = q->task;
1237 
1238         if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
1239                 return;
1240 
1241         /*
1242          * Queue the task for later wakeup for after we've released
1243          * the hb->lock. wake_q_add() grabs reference to p.
1244          */
1245         wake_q_add(wake_q, p);
1246         __unqueue_futex(q);
1247         /*
1248          * The waiting task can free the futex_q as soon as
1249          * q->lock_ptr = NULL is written, without taking any locks. A
1250          * memory barrier is required here to prevent the following
1251          * store to lock_ptr from getting ahead of the plist_del.
1252          */
1253         smp_wmb();
1254         q->lock_ptr = NULL;
1255 }
1256 
1257 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this,
1258                          struct futex_hash_bucket *hb)
1259 {
1260         struct task_struct *new_owner;
1261         struct futex_pi_state *pi_state = this->pi_state;
1262         u32 uninitialized_var(curval), newval;
1263         WAKE_Q(wake_q);
1264         bool deboost;
1265         int ret = 0;
1266 
1267         if (!pi_state)
1268                 return -EINVAL;
1269 
1270         /*
1271          * If current does not own the pi_state then the futex is
1272          * inconsistent and user space fiddled with the futex value.
1273          */
1274         if (pi_state->owner != current)
1275                 return -EINVAL;
1276 
1277         raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
1278         new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
1279 
1280         /*
1281          * It is possible that the next waiter (the one that brought
1282          * this owner to the kernel) timed out and is no longer
1283          * waiting on the lock.
1284          */
1285         if (!new_owner)
1286                 new_owner = this->task;
1287 
1288         /*
1289          * We pass it to the next owner. The WAITERS bit is always
1290          * kept enabled while there is PI state around. We cleanup the
1291          * owner died bit, because we are the owner.
1292          */
1293         newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
1294 
1295         if (unlikely(should_fail_futex(true)))
1296                 ret = -EFAULT;
1297 
1298         if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) {
1299                 ret = -EFAULT;
1300         } else if (curval != uval) {
1301                 /*
1302                  * If a unconditional UNLOCK_PI operation (user space did not
1303                  * try the TID->0 transition) raced with a waiter setting the
1304                  * FUTEX_WAITERS flag between get_user() and locking the hash
1305                  * bucket lock, retry the operation.
1306                  */
1307                 if ((FUTEX_TID_MASK & curval) == uval)
1308                         ret = -EAGAIN;
1309                 else
1310                         ret = -EINVAL;
1311         }
1312         if (ret) {
1313                 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1314                 return ret;
1315         }
1316 
1317         raw_spin_lock(&pi_state->owner->pi_lock);
1318         WARN_ON(list_empty(&pi_state->list));
1319         list_del_init(&pi_state->list);
1320         raw_spin_unlock(&pi_state->owner->pi_lock);
1321 
1322         raw_spin_lock(&new_owner->pi_lock);
1323         WARN_ON(!list_empty(&pi_state->list));
1324         list_add(&pi_state->list, &new_owner->pi_state_list);
1325         pi_state->owner = new_owner;
1326         raw_spin_unlock(&new_owner->pi_lock);
1327 
1328         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1329 
1330         deboost = rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
1331 
1332         /*
1333          * First unlock HB so the waiter does not spin on it once he got woken
1334          * up. Second wake up the waiter before the priority is adjusted. If we
1335          * deboost first (and lose our higher priority), then the task might get
1336          * scheduled away before the wake up can take place.
1337          */
1338         spin_unlock(&hb->lock);
1339         wake_up_q(&wake_q);
1340         if (deboost)
1341                 rt_mutex_adjust_prio(current);
1342 
1343         return 0;
1344 }
1345 
1346 /*
1347  * Express the locking dependencies for lockdep:
1348  */
1349 static inline void
1350 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1351 {
1352         if (hb1 <= hb2) {
1353                 spin_lock(&hb1->lock);
1354                 if (hb1 < hb2)
1355                         spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
1356         } else { /* hb1 > hb2 */
1357                 spin_lock(&hb2->lock);
1358                 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
1359         }
1360 }
1361 
1362 static inline void
1363 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1364 {
1365         spin_unlock(&hb1->lock);
1366         if (hb1 != hb2)
1367                 spin_unlock(&hb2->lock);
1368 }
1369 
1370 /*
1371  * Wake up waiters matching bitset queued on this futex (uaddr).
1372  */
1373 static int
1374 futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
1375 {
1376         struct futex_hash_bucket *hb;
1377         struct futex_q *this, *next;
1378         union futex_key key = FUTEX_KEY_INIT;
1379         int ret;
1380         WAKE_Q(wake_q);
1381 
1382         if (!bitset)
1383                 return -EINVAL;
1384 
1385         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
1386         if (unlikely(ret != 0))
1387                 goto out;
1388 
1389         hb = hash_futex(&key);
1390 
1391         /* Make sure we really have tasks to wakeup */
1392         if (!hb_waiters_pending(hb))
1393                 goto out_put_key;
1394 
1395         spin_lock(&hb->lock);
1396 
1397         plist_for_each_entry_safe(this, next, &hb->chain, list) {
1398                 if (match_futex (&this->key, &key)) {
1399                         if (this->pi_state || this->rt_waiter) {
1400                                 ret = -EINVAL;
1401                                 break;
1402                         }
1403 
1404                         /* Check if one of the bits is set in both bitsets */
1405                         if (!(this->bitset & bitset))
1406                                 continue;
1407 
1408                         mark_wake_futex(&wake_q, this);
1409                         if (++ret >= nr_wake)
1410                                 break;
1411                 }
1412         }
1413 
1414         spin_unlock(&hb->lock);
1415         wake_up_q(&wake_q);
1416 out_put_key:
1417         put_futex_key(&key);
1418 out:
1419         return ret;
1420 }
1421 
1422 /*
1423  * Wake up all waiters hashed on the physical page that is mapped
1424  * to this virtual address:
1425  */
1426 static int
1427 futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
1428               int nr_wake, int nr_wake2, int op)
1429 {
1430         union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1431         struct futex_hash_bucket *hb1, *hb2;
1432         struct futex_q *this, *next;
1433         int ret, op_ret;
1434         WAKE_Q(wake_q);
1435 
1436 retry:
1437         ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1438         if (unlikely(ret != 0))
1439                 goto out;
1440         ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
1441         if (unlikely(ret != 0))
1442                 goto out_put_key1;
1443 
1444         hb1 = hash_futex(&key1);
1445         hb2 = hash_futex(&key2);
1446 
1447 retry_private:
1448         double_lock_hb(hb1, hb2);
1449         op_ret = futex_atomic_op_inuser(op, uaddr2);
1450         if (unlikely(op_ret < 0)) {
1451 
1452                 double_unlock_hb(hb1, hb2);
1453 
1454 #ifndef CONFIG_MMU
1455                 /*
1456                  * we don't get EFAULT from MMU faults if we don't have an MMU,
1457                  * but we might get them from range checking
1458                  */
1459                 ret = op_ret;
1460                 goto out_put_keys;
1461 #endif
1462 
1463                 if (unlikely(op_ret != -EFAULT)) {
1464                         ret = op_ret;
1465                         goto out_put_keys;
1466                 }
1467 
1468                 ret = fault_in_user_writeable(uaddr2);
1469                 if (ret)
1470                         goto out_put_keys;
1471 
1472                 if (!(flags & FLAGS_SHARED))
1473                         goto retry_private;
1474 
1475                 put_futex_key(&key2);
1476                 put_futex_key(&key1);
1477                 goto retry;
1478         }
1479 
1480         plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1481                 if (match_futex (&this->key, &key1)) {
1482                         if (this->pi_state || this->rt_waiter) {
1483                                 ret = -EINVAL;
1484                                 goto out_unlock;
1485                         }
1486                         mark_wake_futex(&wake_q, this);
1487                         if (++ret >= nr_wake)
1488                                 break;
1489                 }
1490         }
1491 
1492         if (op_ret > 0) {
1493                 op_ret = 0;
1494                 plist_for_each_entry_safe(this, next, &hb2->chain, list) {
1495                         if (match_futex (&this->key, &key2)) {
1496                                 if (this->pi_state || this->rt_waiter) {
1497                                         ret = -EINVAL;
1498                                         goto out_unlock;
1499                                 }
1500                                 mark_wake_futex(&wake_q, this);
1501                                 if (++op_ret >= nr_wake2)
1502                                         break;
1503                         }
1504                 }
1505                 ret += op_ret;
1506         }
1507 
1508 out_unlock:
1509         double_unlock_hb(hb1, hb2);
1510         wake_up_q(&wake_q);
1511 out_put_keys:
1512         put_futex_key(&key2);
1513 out_put_key1:
1514         put_futex_key(&key1);
1515 out:
1516         return ret;
1517 }
1518 
1519 /**
1520  * requeue_futex() - Requeue a futex_q from one hb to another
1521  * @q:          the futex_q to requeue
1522  * @hb1:        the source hash_bucket
1523  * @hb2:        the target hash_bucket
1524  * @key2:       the new key for the requeued futex_q
1525  */
1526 static inline
1527 void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1528                    struct futex_hash_bucket *hb2, union futex_key *key2)
1529 {
1530 
1531         /*
1532          * If key1 and key2 hash to the same bucket, no need to
1533          * requeue.
1534          */
1535         if (likely(&hb1->chain != &hb2->chain)) {
1536                 plist_del(&q->list, &hb1->chain);
1537                 hb_waiters_dec(hb1);
1538                 hb_waiters_inc(hb2);
1539                 plist_add(&q->list, &hb2->chain);
1540                 q->lock_ptr = &hb2->lock;
1541         }
1542         get_futex_key_refs(key2);
1543         q->key = *key2;
1544 }
1545 
1546 /**
1547  * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1548  * @q:          the futex_q
1549  * @key:        the key of the requeue target futex
1550  * @hb:         the hash_bucket of the requeue target futex
1551  *
1552  * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1553  * target futex if it is uncontended or via a lock steal.  Set the futex_q key
1554  * to the requeue target futex so the waiter can detect the wakeup on the right
1555  * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1556  * atomic lock acquisition.  Set the q->lock_ptr to the requeue target hb->lock
1557  * to protect access to the pi_state to fixup the owner later.  Must be called
1558  * with both q->lock_ptr and hb->lock held.
1559  */
1560 static inline
1561 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1562                            struct futex_hash_bucket *hb)
1563 {
1564         get_futex_key_refs(key);
1565         q->key = *key;
1566 
1567         __unqueue_futex(q);
1568 
1569         WARN_ON(!q->rt_waiter);
1570         q->rt_waiter = NULL;
1571 
1572         q->lock_ptr = &hb->lock;
1573 
1574         wake_up_state(q->task, TASK_NORMAL);
1575 }
1576 
1577 /**
1578  * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1579  * @pifutex:            the user address of the to futex
1580  * @hb1:                the from futex hash bucket, must be locked by the caller
1581  * @hb2:                the to futex hash bucket, must be locked by the caller
1582  * @key1:               the from futex key
1583  * @key2:               the to futex key
1584  * @ps:                 address to store the pi_state pointer
1585  * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
1586  *
1587  * Try and get the lock on behalf of the top waiter if we can do it atomically.
1588  * Wake the top waiter if we succeed.  If the caller specified set_waiters,
1589  * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1590  * hb1 and hb2 must be held by the caller.
1591  *
1592  * Return:
1593  *  0 - failed to acquire the lock atomically;
1594  * >0 - acquired the lock, return value is vpid of the top_waiter
1595  * <0 - error
1596  */
1597 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1598                                  struct futex_hash_bucket *hb1,
1599                                  struct futex_hash_bucket *hb2,
1600                                  union futex_key *key1, union futex_key *key2,
1601                                  struct futex_pi_state **ps, int set_waiters)
1602 {
1603         struct futex_q *top_waiter = NULL;
1604         u32 curval;
1605         int ret, vpid;
1606 
1607         if (get_futex_value_locked(&curval, pifutex))
1608                 return -EFAULT;
1609 
1610         if (unlikely(should_fail_futex(true)))
1611                 return -EFAULT;
1612 
1613         /*
1614          * Find the top_waiter and determine if there are additional waiters.
1615          * If the caller intends to requeue more than 1 waiter to pifutex,
1616          * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1617          * as we have means to handle the possible fault.  If not, don't set
1618          * the bit unecessarily as it will force the subsequent unlock to enter
1619          * the kernel.
1620          */
1621         top_waiter = futex_top_waiter(hb1, key1);
1622 
1623         /* There are no waiters, nothing for us to do. */
1624         if (!top_waiter)
1625                 return 0;
1626 
1627         /* Ensure we requeue to the expected futex. */
1628         if (!match_futex(top_waiter->requeue_pi_key, key2))
1629                 return -EINVAL;
1630 
1631         /*
1632          * Try to take the lock for top_waiter.  Set the FUTEX_WAITERS bit in
1633          * the contended case or if set_waiters is 1.  The pi_state is returned
1634          * in ps in contended cases.
1635          */
1636         vpid = task_pid_vnr(top_waiter->task);
1637         ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1638                                    set_waiters);
1639         if (ret == 1) {
1640                 requeue_pi_wake_futex(top_waiter, key2, hb2);
1641                 return vpid;
1642         }
1643         return ret;
1644 }
1645 
1646 /**
1647  * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1648  * @uaddr1:     source futex user address
1649  * @flags:      futex flags (FLAGS_SHARED, etc.)
1650  * @uaddr2:     target futex user address
1651  * @nr_wake:    number of waiters to wake (must be 1 for requeue_pi)
1652  * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1653  * @cmpval:     @uaddr1 expected value (or %NULL)
1654  * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
1655  *              pi futex (pi to pi requeue is not supported)
1656  *
1657  * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1658  * uaddr2 atomically on behalf of the top waiter.
1659  *
1660  * Return:
1661  * >=0 - on success, the number of tasks requeued or woken;
1662  *  <0 - on error
1663  */
1664 static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
1665                          u32 __user *uaddr2, int nr_wake, int nr_requeue,
1666                          u32 *cmpval, int requeue_pi)
1667 {
1668         union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1669         int drop_count = 0, task_count = 0, ret;
1670         struct futex_pi_state *pi_state = NULL;
1671         struct futex_hash_bucket *hb1, *hb2;
1672         struct futex_q *this, *next;
1673         WAKE_Q(wake_q);
1674 
1675         if (requeue_pi) {
1676                 /*
1677                  * Requeue PI only works on two distinct uaddrs. This
1678                  * check is only valid for private futexes. See below.
1679                  */
1680                 if (uaddr1 == uaddr2)
1681                         return -EINVAL;
1682 
1683                 /*
1684                  * requeue_pi requires a pi_state, try to allocate it now
1685                  * without any locks in case it fails.
1686                  */
1687                 if (refill_pi_state_cache())
1688                         return -ENOMEM;
1689                 /*
1690                  * requeue_pi must wake as many tasks as it can, up to nr_wake
1691                  * + nr_requeue, since it acquires the rt_mutex prior to
1692                  * returning to userspace, so as to not leave the rt_mutex with
1693                  * waiters and no owner.  However, second and third wake-ups
1694                  * cannot be predicted as they involve race conditions with the
1695                  * first wake and a fault while looking up the pi_state.  Both
1696                  * pthread_cond_signal() and pthread_cond_broadcast() should
1697                  * use nr_wake=1.
1698                  */
1699                 if (nr_wake != 1)
1700                         return -EINVAL;
1701         }
1702 
1703 retry:
1704         ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1705         if (unlikely(ret != 0))
1706                 goto out;
1707         ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
1708                             requeue_pi ? VERIFY_WRITE : VERIFY_READ);
1709         if (unlikely(ret != 0))
1710                 goto out_put_key1;
1711 
1712         /*
1713          * The check above which compares uaddrs is not sufficient for
1714          * shared futexes. We need to compare the keys:
1715          */
1716         if (requeue_pi && match_futex(&key1, &key2)) {
1717                 ret = -EINVAL;
1718                 goto out_put_keys;
1719         }
1720 
1721         hb1 = hash_futex(&key1);
1722         hb2 = hash_futex(&key2);
1723 
1724 retry_private:
1725         hb_waiters_inc(hb2);
1726         double_lock_hb(hb1, hb2);
1727 
1728         if (likely(cmpval != NULL)) {
1729                 u32 curval;
1730 
1731                 ret = get_futex_value_locked(&curval, uaddr1);
1732 
1733                 if (unlikely(ret)) {
1734                         double_unlock_hb(hb1, hb2);
1735                         hb_waiters_dec(hb2);
1736 
1737                         ret = get_user(curval, uaddr1);
1738                         if (ret)
1739                                 goto out_put_keys;
1740 
1741                         if (!(flags & FLAGS_SHARED))
1742                                 goto retry_private;
1743 
1744                         put_futex_key(&key2);
1745                         put_futex_key(&key1);
1746                         goto retry;
1747                 }
1748                 if (curval != *cmpval) {
1749                         ret = -EAGAIN;
1750                         goto out_unlock;
1751                 }
1752         }
1753 
1754         if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1755                 /*
1756                  * Attempt to acquire uaddr2 and wake the top waiter. If we
1757                  * intend to requeue waiters, force setting the FUTEX_WAITERS
1758                  * bit.  We force this here where we are able to easily handle
1759                  * faults rather in the requeue loop below.
1760                  */
1761                 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1762                                                  &key2, &pi_state, nr_requeue);
1763 
1764                 /*
1765                  * At this point the top_waiter has either taken uaddr2 or is
1766                  * waiting on it.  If the former, then the pi_state will not
1767                  * exist yet, look it up one more time to ensure we have a
1768                  * reference to it. If the lock was taken, ret contains the
1769                  * vpid of the top waiter task.
1770                  * If the lock was not taken, we have pi_state and an initial
1771                  * refcount on it. In case of an error we have nothing.
1772                  */
1773                 if (ret > 0) {
1774                         WARN_ON(pi_state);
1775                         drop_count++;
1776                         task_count++;
1777                         /*
1778                          * If we acquired the lock, then the user space value
1779                          * of uaddr2 should be vpid. It cannot be changed by
1780                          * the top waiter as it is blocked on hb2 lock if it
1781                          * tries to do so. If something fiddled with it behind
1782                          * our back the pi state lookup might unearth it. So
1783                          * we rather use the known value than rereading and
1784                          * handing potential crap to lookup_pi_state.
1785                          *
1786                          * If that call succeeds then we have pi_state and an
1787                          * initial refcount on it.
1788                          */
1789                         ret = lookup_pi_state(ret, hb2, &key2, &pi_state);
1790                 }
1791 
1792                 switch (ret) {
1793                 case 0:
1794                         /* We hold a reference on the pi state. */
1795                         break;
1796 
1797                         /* If the above failed, then pi_state is NULL */
1798                 case -EFAULT:
1799                         double_unlock_hb(hb1, hb2);
1800                         hb_waiters_dec(hb2);
1801                         put_futex_key(&key2);
1802                         put_futex_key(&key1);
1803                         ret = fault_in_user_writeable(uaddr2);
1804                         if (!ret)
1805                                 goto retry;
1806                         goto out;
1807                 case -EAGAIN:
1808                         /*
1809                          * Two reasons for this:
1810                          * - Owner is exiting and we just wait for the
1811                          *   exit to complete.
1812                          * - The user space value changed.
1813                          */
1814                         double_unlock_hb(hb1, hb2);
1815                         hb_waiters_dec(hb2);
1816                         put_futex_key(&key2);
1817                         put_futex_key(&key1);
1818                         cond_resched();
1819                         goto retry;
1820                 default:
1821                         goto out_unlock;
1822                 }
1823         }
1824 
1825         plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1826                 if (task_count - nr_wake >= nr_requeue)
1827                         break;
1828 
1829                 if (!match_futex(&this->key, &key1))
1830                         continue;
1831 
1832                 /*
1833                  * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
1834                  * be paired with each other and no other futex ops.
1835                  *
1836                  * We should never be requeueing a futex_q with a pi_state,
1837                  * which is awaiting a futex_unlock_pi().
1838                  */
1839                 if ((requeue_pi && !this->rt_waiter) ||
1840                     (!requeue_pi && this->rt_waiter) ||
1841                     this->pi_state) {
1842                         ret = -EINVAL;
1843                         break;
1844                 }
1845 
1846                 /*
1847                  * Wake nr_wake waiters.  For requeue_pi, if we acquired the
1848                  * lock, we already woke the top_waiter.  If not, it will be
1849                  * woken by futex_unlock_pi().
1850                  */
1851                 if (++task_count <= nr_wake && !requeue_pi) {
1852                         mark_wake_futex(&wake_q, this);
1853                         continue;
1854                 }
1855 
1856                 /* Ensure we requeue to the expected futex for requeue_pi. */
1857                 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
1858                         ret = -EINVAL;
1859                         break;
1860                 }
1861 
1862                 /*
1863                  * Requeue nr_requeue waiters and possibly one more in the case
1864                  * of requeue_pi if we couldn't acquire the lock atomically.
1865                  */
1866                 if (requeue_pi) {
1867                         /*
1868                          * Prepare the waiter to take the rt_mutex. Take a
1869                          * refcount on the pi_state and store the pointer in
1870                          * the futex_q object of the waiter.
1871                          */
1872                         atomic_inc(&pi_state->refcount);
1873                         this->pi_state = pi_state;
1874                         ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1875                                                         this->rt_waiter,
1876                                                         this->task);
1877                         if (ret == 1) {
1878                                 /*
1879                                  * We got the lock. We do neither drop the
1880                                  * refcount on pi_state nor clear
1881                                  * this->pi_state because the waiter needs the
1882                                  * pi_state for cleaning up the user space
1883                                  * value. It will drop the refcount after
1884                                  * doing so.
1885                                  */
1886                                 requeue_pi_wake_futex(this, &key2, hb2);
1887                                 drop_count++;
1888                                 continue;
1889                         } else if (ret) {
1890                                 /*
1891                                  * rt_mutex_start_proxy_lock() detected a
1892                                  * potential deadlock when we tried to queue
1893                                  * that waiter. Drop the pi_state reference
1894                                  * which we took above and remove the pointer
1895                                  * to the state from the waiters futex_q
1896                                  * object.
1897                                  */
1898                                 this->pi_state = NULL;
1899                                 put_pi_state(pi_state);
1900                                 /*
1901                                  * We stop queueing more waiters and let user
1902                                  * space deal with the mess.
1903                                  */
1904                                 break;
1905                         }
1906                 }
1907                 requeue_futex(this, hb1, hb2, &key2);
1908                 drop_count++;
1909         }
1910 
1911         /*
1912          * We took an extra initial reference to the pi_state either
1913          * in futex_proxy_trylock_atomic() or in lookup_pi_state(). We
1914          * need to drop it here again.
1915          */
1916         put_pi_state(pi_state);
1917 
1918 out_unlock:
1919         double_unlock_hb(hb1, hb2);
1920         wake_up_q(&wake_q);
1921         hb_waiters_dec(hb2);
1922 
1923         /*
1924          * drop_futex_key_refs() must be called outside the spinlocks. During
1925          * the requeue we moved futex_q's from the hash bucket at key1 to the
1926          * one at key2 and updated their key pointer.  We no longer need to
1927          * hold the references to key1.
1928          */
1929         while (--drop_count >= 0)
1930                 drop_futex_key_refs(&key1);
1931 
1932 out_put_keys:
1933         put_futex_key(&key2);
1934 out_put_key1:
1935         put_futex_key(&key1);
1936 out:
1937         return ret ? ret : task_count;
1938 }
1939 
1940 /* The key must be already stored in q->key. */
1941 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
1942         __acquires(&hb->lock)
1943 {
1944         struct futex_hash_bucket *hb;
1945 
1946         hb = hash_futex(&q->key);
1947 
1948         /*
1949          * Increment the counter before taking the lock so that
1950          * a potential waker won't miss a to-be-slept task that is
1951          * waiting for the spinlock. This is safe as all queue_lock()
1952          * users end up calling queue_me(). Similarly, for housekeeping,
1953          * decrement the counter at queue_unlock() when some error has
1954          * occurred and we don't end up adding the task to the list.
1955          */
1956         hb_waiters_inc(hb);
1957 
1958         q->lock_ptr = &hb->lock;
1959 
1960         spin_lock(&hb->lock); /* implies smp_mb(); (A) */
1961         return hb;
1962 }
1963 
1964 static inline void
1965 queue_unlock(struct futex_hash_bucket *hb)
1966         __releases(&hb->lock)
1967 {
1968         spin_unlock(&hb->lock);
1969         hb_waiters_dec(hb);
1970 }
1971 
1972 /**
1973  * queue_me() - Enqueue the futex_q on the futex_hash_bucket
1974  * @q:  The futex_q to enqueue
1975  * @hb: The destination hash bucket
1976  *
1977  * The hb->lock must be held by the caller, and is released here. A call to
1978  * queue_me() is typically paired with exactly one call to unqueue_me().  The
1979  * exceptions involve the PI related operations, which may use unqueue_me_pi()
1980  * or nothing if the unqueue is done as part of the wake process and the unqueue
1981  * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1982  * an example).
1983  */
1984 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
1985         __releases(&hb->lock)
1986 {
1987         int prio;
1988 
1989         /*
1990          * The priority used to register this element is
1991          * - either the real thread-priority for the real-time threads
1992          * (i.e. threads with a priority lower than MAX_RT_PRIO)
1993          * - or MAX_RT_PRIO for non-RT threads.
1994          * Thus, all RT-threads are woken first in priority order, and
1995          * the others are woken last, in FIFO order.
1996          */
1997         prio = min(current->normal_prio, MAX_RT_PRIO);
1998 
1999         plist_node_init(&q->list, prio);
2000         plist_add(&q->list, &hb->chain);
2001         q->task = current;
2002         spin_unlock(&hb->lock);
2003 }
2004 
2005 /**
2006  * unqueue_me() - Remove the futex_q from its futex_hash_bucket
2007  * @q:  The futex_q to unqueue
2008  *
2009  * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
2010  * be paired with exactly one earlier call to queue_me().
2011  *
2012  * Return:
2013  *   1 - if the futex_q was still queued (and we removed unqueued it);
2014  *   0 - if the futex_q was already removed by the waking thread
2015  */
2016 static int unqueue_me(struct futex_q *q)
2017 {
2018         spinlock_t *lock_ptr;
2019         int ret = 0;
2020 
2021         /* In the common case we don't take the spinlock, which is nice. */
2022 retry:
2023         /*
2024          * q->lock_ptr can change between this read and the following spin_lock.
2025          * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
2026          * optimizing lock_ptr out of the logic below.
2027          */
2028         lock_ptr = READ_ONCE(q->lock_ptr);
2029         if (lock_ptr != NULL) {
2030                 spin_lock(lock_ptr);
2031                 /*
2032                  * q->lock_ptr can change between reading it and
2033                  * spin_lock(), causing us to take the wrong lock.  This
2034                  * corrects the race condition.
2035                  *
2036                  * Reasoning goes like this: if we have the wrong lock,
2037                  * q->lock_ptr must have changed (maybe several times)
2038                  * between reading it and the spin_lock().  It can
2039                  * change again after the spin_lock() but only if it was
2040                  * already changed before the spin_lock().  It cannot,
2041                  * however, change back to the original value.  Therefore
2042                  * we can detect whether we acquired the correct lock.
2043                  */
2044                 if (unlikely(lock_ptr != q->lock_ptr)) {
2045                         spin_unlock(lock_ptr);
2046                         goto retry;
2047                 }
2048                 __unqueue_futex(q);
2049 
2050                 BUG_ON(q->pi_state);
2051 
2052                 spin_unlock(lock_ptr);
2053                 ret = 1;
2054         }
2055 
2056         drop_futex_key_refs(&q->key);
2057         return ret;
2058 }
2059 
2060 /*
2061  * PI futexes can not be requeued and must remove themself from the
2062  * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
2063  * and dropped here.
2064  */
2065 static void unqueue_me_pi(struct futex_q *q)
2066         __releases(q->lock_ptr)
2067 {
2068         __unqueue_futex(q);
2069 
2070         BUG_ON(!q->pi_state);
2071         put_pi_state(q->pi_state);
2072         q->pi_state = NULL;
2073 
2074         spin_unlock(q->lock_ptr);
2075 }
2076 
2077 /*
2078  * Fixup the pi_state owner with the new owner.
2079  *
2080  * Must be called with hash bucket lock held and mm->sem held for non
2081  * private futexes.
2082  */
2083 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
2084                                 struct task_struct *newowner)
2085 {
2086         u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
2087         struct futex_pi_state *pi_state = q->pi_state;
2088         struct task_struct *oldowner = pi_state->owner;
2089         u32 uval, uninitialized_var(curval), newval;
2090         int ret;
2091 
2092         /* Owner died? */
2093         if (!pi_state->owner)
2094                 newtid |= FUTEX_OWNER_DIED;
2095 
2096         /*
2097          * We are here either because we stole the rtmutex from the
2098          * previous highest priority waiter or we are the highest priority
2099          * waiter but failed to get the rtmutex the first time.
2100          * We have to replace the newowner TID in the user space variable.
2101          * This must be atomic as we have to preserve the owner died bit here.
2102          *
2103          * Note: We write the user space value _before_ changing the pi_state
2104          * because we can fault here. Imagine swapped out pages or a fork
2105          * that marked all the anonymous memory readonly for cow.
2106          *
2107          * Modifying pi_state _before_ the user space value would
2108          * leave the pi_state in an inconsistent state when we fault
2109          * here, because we need to drop the hash bucket lock to
2110          * handle the fault. This might be observed in the PID check
2111          * in lookup_pi_state.
2112          */
2113 retry:
2114         if (get_futex_value_locked(&uval, uaddr))
2115                 goto handle_fault;
2116 
2117         while (1) {
2118                 newval = (uval & FUTEX_OWNER_DIED) | newtid;
2119 
2120                 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
2121                         goto handle_fault;
2122                 if (curval == uval)
2123                         break;
2124                 uval = curval;
2125         }
2126 
2127         /*
2128          * We fixed up user space. Now we need to fix the pi_state
2129          * itself.
2130          */
2131         if (pi_state->owner != NULL) {
2132                 raw_spin_lock_irq(&pi_state->owner->pi_lock);
2133                 WARN_ON(list_empty(&pi_state->list));
2134                 list_del_init(&pi_state->list);
2135                 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
2136         }
2137 
2138         pi_state->owner = newowner;
2139 
2140         raw_spin_lock_irq(&newowner->pi_lock);
2141         WARN_ON(!list_empty(&pi_state->list));
2142         list_add(&pi_state->list, &newowner->pi_state_list);
2143         raw_spin_unlock_irq(&newowner->pi_lock);
2144         return 0;
2145 
2146         /*
2147          * To handle the page fault we need to drop the hash bucket
2148          * lock here. That gives the other task (either the highest priority
2149          * waiter itself or the task which stole the rtmutex) the
2150          * chance to try the fixup of the pi_state. So once we are
2151          * back from handling the fault we need to check the pi_state
2152          * after reacquiring the hash bucket lock and before trying to
2153          * do another fixup. When the fixup has been done already we
2154          * simply return.
2155          */
2156 handle_fault:
2157         spin_unlock(q->lock_ptr);
2158 
2159         ret = fault_in_user_writeable(uaddr);
2160 
2161         spin_lock(q->lock_ptr);
2162 
2163         /*
2164          * Check if someone else fixed it for us:
2165          */
2166         if (pi_state->owner != oldowner)
2167                 return 0;
2168 
2169         if (ret)
2170                 return ret;
2171 
2172         goto retry;
2173 }
2174 
2175 static long futex_wait_restart(struct restart_block *restart);
2176 
2177 /**
2178  * fixup_owner() - Post lock pi_state and corner case management
2179  * @uaddr:      user address of the futex
2180  * @q:          futex_q (contains pi_state and access to the rt_mutex)
2181  * @locked:     if the attempt to take the rt_mutex succeeded (1) or not (0)
2182  *
2183  * After attempting to lock an rt_mutex, this function is called to cleanup
2184  * the pi_state owner as well as handle race conditions that may allow us to
2185  * acquire the lock. Must be called with the hb lock held.
2186  *
2187  * Return:
2188  *  1 - success, lock taken;
2189  *  0 - success, lock not taken;
2190  * <0 - on error (-EFAULT)
2191  */
2192 static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
2193 {
2194         struct task_struct *owner;
2195         int ret = 0;
2196 
2197         if (locked) {
2198                 /*
2199                  * Got the lock. We might not be the anticipated owner if we
2200                  * did a lock-steal - fix up the PI-state in that case:
2201                  */
2202                 if (q->pi_state->owner != current)
2203                         ret = fixup_pi_state_owner(uaddr, q, current);
2204                 goto out;
2205         }
2206 
2207         /*
2208          * Catch the rare case, where the lock was released when we were on the
2209          * way back before we locked the hash bucket.
2210          */
2211         if (q->pi_state->owner == current) {
2212                 /*
2213                  * Try to get the rt_mutex now. This might fail as some other
2214                  * task acquired the rt_mutex after we removed ourself from the
2215                  * rt_mutex waiters list.
2216                  */
2217                 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
2218                         locked = 1;
2219                         goto out;
2220                 }
2221 
2222                 /*
2223                  * pi_state is incorrect, some other task did a lock steal and
2224                  * we returned due to timeout or signal without taking the
2225                  * rt_mutex. Too late.
2226                  */
2227                 raw_spin_lock_irq(&q->pi_state->pi_mutex.wait_lock);
2228                 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
2229                 if (!owner)
2230                         owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
2231                 raw_spin_unlock_irq(&q->pi_state->pi_mutex.wait_lock);
2232                 ret = fixup_pi_state_owner(uaddr, q, owner);
2233                 goto out;
2234         }
2235 
2236         /*
2237          * Paranoia check. If we did not take the lock, then we should not be
2238          * the owner of the rt_mutex.
2239          */
2240         if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
2241                 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
2242                                 "pi-state %p\n", ret,
2243                                 q->pi_state->pi_mutex.owner,
2244                                 q->pi_state->owner);
2245 
2246 out:
2247         return ret ? ret : locked;
2248 }
2249 
2250 /**
2251  * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
2252  * @hb:         the futex hash bucket, must be locked by the caller
2253  * @q:          the futex_q to queue up on
2254  * @timeout:    the prepared hrtimer_sleeper, or null for no timeout
2255  */
2256 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
2257                                 struct hrtimer_sleeper *timeout)
2258 {
2259         /*
2260          * The task state is guaranteed to be set before another task can
2261          * wake it. set_current_state() is implemented using smp_store_mb() and
2262          * queue_me() calls spin_unlock() upon completion, both serializing
2263          * access to the hash list and forcing another memory barrier.
2264          */
2265         set_current_state(TASK_INTERRUPTIBLE);
2266         queue_me(q, hb);
2267 
2268         /* Arm the timer */
2269         if (timeout)
2270                 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
2271 
2272         /*
2273          * If we have been removed from the hash list, then another task
2274          * has tried to wake us, and we can skip the call to schedule().
2275          */
2276         if (likely(!plist_node_empty(&q->list))) {
2277                 /*
2278                  * If the timer has already expired, current will already be
2279                  * flagged for rescheduling. Only call schedule if there
2280                  * is no timeout, or if it has yet to expire.
2281                  */
2282                 if (!timeout || timeout->task)
2283                         freezable_schedule();
2284         }
2285         __set_current_state(TASK_RUNNING);
2286 }
2287 
2288 /**
2289  * futex_wait_setup() - Prepare to wait on a futex
2290  * @uaddr:      the futex userspace address
2291  * @val:        the expected value
2292  * @flags:      futex flags (FLAGS_SHARED, etc.)
2293  * @q:          the associated futex_q
2294  * @hb:         storage for hash_bucket pointer to be returned to caller
2295  *
2296  * Setup the futex_q and locate the hash_bucket.  Get the futex value and
2297  * compare it with the expected value.  Handle atomic faults internally.
2298  * Return with the hb lock held and a q.key reference on success, and unlocked
2299  * with no q.key reference on failure.
2300  *
2301  * Return:
2302  *  0 - uaddr contains val and hb has been locked;
2303  * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
2304  */
2305 static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
2306                            struct futex_q *q, struct futex_hash_bucket **hb)
2307 {
2308         u32 uval;
2309         int ret;
2310 
2311         /*
2312          * Access the page AFTER the hash-bucket is locked.
2313          * Order is important:
2314          *
2315          *   Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
2316          *   Userspace waker:  if (cond(var)) { var = new; futex_wake(&var); }
2317          *
2318          * The basic logical guarantee of a futex is that it blocks ONLY
2319          * if cond(var) is known to be true at the time of blocking, for
2320          * any cond.  If we locked the hash-bucket after testing *uaddr, that
2321          * would open a race condition where we could block indefinitely with
2322          * cond(var) false, which would violate the guarantee.
2323          *
2324          * On the other hand, we insert q and release the hash-bucket only
2325          * after testing *uaddr.  This guarantees that futex_wait() will NOT
2326          * absorb a wakeup if *uaddr does not match the desired values
2327          * while the syscall executes.
2328          */
2329 retry:
2330         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
2331         if (unlikely(ret != 0))
2332                 return ret;
2333 
2334 retry_private:
2335         *hb = queue_lock(q);
2336 
2337         ret = get_futex_value_locked(&uval, uaddr);
2338 
2339         if (ret) {
2340                 queue_unlock(*hb);
2341 
2342                 ret = get_user(uval, uaddr);
2343                 if (ret)
2344                         goto out;
2345 
2346                 if (!(flags & FLAGS_SHARED))
2347                         goto retry_private;
2348 
2349                 put_futex_key(&q->key);
2350                 goto retry;
2351         }
2352 
2353         if (uval != val) {
2354                 queue_unlock(*hb);
2355                 ret = -EWOULDBLOCK;
2356         }
2357 
2358 out:
2359         if (ret)
2360                 put_futex_key(&q->key);
2361         return ret;
2362 }
2363 
2364 static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
2365                       ktime_t *abs_time, u32 bitset)
2366 {
2367         struct hrtimer_sleeper timeout, *to = NULL;
2368         struct restart_block *restart;
2369         struct futex_hash_bucket *hb;
2370         struct futex_q q = futex_q_init;
2371         int ret;
2372 
2373         if (!bitset)
2374                 return -EINVAL;
2375         q.bitset = bitset;
2376 
2377         if (abs_time) {
2378                 to = &timeout;
2379 
2380                 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2381                                       CLOCK_REALTIME : CLOCK_MONOTONIC,
2382                                       HRTIMER_MODE_ABS);
2383                 hrtimer_init_sleeper(to, current);
2384                 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2385                                              current->timer_slack_ns);
2386         }
2387 
2388 retry:
2389         /*
2390          * Prepare to wait on uaddr. On success, holds hb lock and increments
2391          * q.key refs.
2392          */
2393         ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2394         if (ret)
2395                 goto out;
2396 
2397         /* queue_me and wait for wakeup, timeout, or a signal. */
2398         futex_wait_queue_me(hb, &q, to);
2399 
2400         /* If we were woken (and unqueued), we succeeded, whatever. */
2401         ret = 0;
2402         /* unqueue_me() drops q.key ref */
2403         if (!unqueue_me(&q))
2404                 goto out;
2405         ret = -ETIMEDOUT;
2406         if (to && !to->task)
2407                 goto out;
2408 
2409         /*
2410          * We expect signal_pending(current), but we might be the
2411          * victim of a spurious wakeup as well.
2412          */
2413         if (!signal_pending(current))
2414                 goto retry;
2415 
2416         ret = -ERESTARTSYS;
2417         if (!abs_time)
2418                 goto out;
2419 
2420         restart = &current->restart_block;
2421         restart->fn = futex_wait_restart;
2422         restart->futex.uaddr = uaddr;
2423         restart->futex.val = val;
2424         restart->futex.time = abs_time->tv64;
2425         restart->futex.bitset = bitset;
2426         restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
2427 
2428         ret = -ERESTART_RESTARTBLOCK;
2429 
2430 out:
2431         if (to) {
2432                 hrtimer_cancel(&to->timer);
2433                 destroy_hrtimer_on_stack(&to->timer);
2434         }
2435         return ret;
2436 }
2437 
2438 
2439 static long futex_wait_restart(struct restart_block *restart)
2440 {
2441         u32 __user *uaddr = restart->futex.uaddr;
2442         ktime_t t, *tp = NULL;
2443 
2444         if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
2445                 t.tv64 = restart->futex.time;
2446                 tp = &t;
2447         }
2448         restart->fn = do_no_restart_syscall;
2449 
2450         return (long)futex_wait(uaddr, restart->futex.flags,
2451                                 restart->futex.val, tp, restart->futex.bitset);
2452 }
2453 
2454 
2455 /*
2456  * Userspace tried a 0 -> TID atomic transition of the futex value
2457  * and failed. The kernel side here does the whole locking operation:
2458  * if there are waiters then it will block as a consequence of relying
2459  * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
2460  * a 0 value of the futex too.).
2461  *
2462  * Also serves as futex trylock_pi()'ing, and due semantics.
2463  */
2464 static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
2465                          ktime_t *time, int trylock)
2466 {
2467         struct hrtimer_sleeper timeout, *to = NULL;
2468         struct futex_hash_bucket *hb;
2469         struct futex_q q = futex_q_init;
2470         int res, ret;
2471 
2472         if (refill_pi_state_cache())
2473                 return -ENOMEM;
2474 
2475         if (time) {
2476                 to = &timeout;
2477                 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
2478                                       HRTIMER_MODE_ABS);
2479                 hrtimer_init_sleeper(to, current);
2480                 hrtimer_set_expires(&to->timer, *time);
2481         }
2482 
2483 retry:
2484         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
2485         if (unlikely(ret != 0))
2486                 goto out;
2487 
2488 retry_private:
2489         hb = queue_lock(&q);
2490 
2491         ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
2492         if (unlikely(ret)) {
2493                 /*
2494                  * Atomic work succeeded and we got the lock,
2495                  * or failed. Either way, we do _not_ block.
2496                  */
2497                 switch (ret) {
2498                 case 1:
2499                         /* We got the lock. */
2500                         ret = 0;
2501                         goto out_unlock_put_key;
2502                 case -EFAULT:
2503                         goto uaddr_faulted;
2504                 case -EAGAIN:
2505                         /*
2506                          * Two reasons for this:
2507                          * - Task is exiting and we just wait for the
2508                          *   exit to complete.
2509                          * - The user space value changed.
2510                          */
2511                         queue_unlock(hb);
2512                         put_futex_key(&q.key);
2513                         cond_resched();
2514                         goto retry;
2515                 default:
2516                         goto out_unlock_put_key;
2517                 }
2518         }
2519 
2520         /*
2521          * Only actually queue now that the atomic ops are done:
2522          */
2523         queue_me(&q, hb);
2524 
2525         WARN_ON(!q.pi_state);
2526         /*
2527          * Block on the PI mutex:
2528          */
2529         if (!trylock) {
2530                 ret = rt_mutex_timed_futex_lock(&q.pi_state->pi_mutex, to);
2531         } else {
2532                 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
2533                 /* Fixup the trylock return value: */
2534                 ret = ret ? 0 : -EWOULDBLOCK;
2535         }
2536 
2537         spin_lock(q.lock_ptr);
2538         /*
2539          * Fixup the pi_state owner and possibly acquire the lock if we
2540          * haven't already.
2541          */
2542         res = fixup_owner(uaddr, &q, !ret);
2543         /*
2544          * If fixup_owner() returned an error, proprogate that.  If it acquired
2545          * the lock, clear our -ETIMEDOUT or -EINTR.
2546          */
2547         if (res)
2548                 ret = (res < 0) ? res : 0;
2549 
2550         /*
2551          * If fixup_owner() faulted and was unable to handle the fault, unlock
2552          * it and return the fault to userspace.
2553          */
2554         if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
2555                 rt_mutex_unlock(&q.pi_state->pi_mutex);
2556 
2557         /* Unqueue and drop the lock */
2558         unqueue_me_pi(&q);
2559 
2560         goto out_put_key;
2561 
2562 out_unlock_put_key:
2563         queue_unlock(hb);
2564 
2565 out_put_key:
2566         put_futex_key(&q.key);
2567 out:
2568         if (to)
2569                 destroy_hrtimer_on_stack(&to->timer);
2570         return ret != -EINTR ? ret : -ERESTARTNOINTR;
2571 
2572 uaddr_faulted:
2573         queue_unlock(hb);
2574 
2575         ret = fault_in_user_writeable(uaddr);
2576         if (ret)
2577                 goto out_put_key;
2578 
2579         if (!(flags & FLAGS_SHARED))
2580                 goto retry_private;
2581 
2582         put_futex_key(&q.key);
2583         goto retry;
2584 }
2585 
2586 /*
2587  * Userspace attempted a TID -> 0 atomic transition, and failed.
2588  * This is the in-kernel slowpath: we look up the PI state (if any),
2589  * and do the rt-mutex unlock.
2590  */
2591 static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
2592 {
2593         u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current);
2594         union futex_key key = FUTEX_KEY_INIT;
2595         struct futex_hash_bucket *hb;
2596         struct futex_q *match;
2597         int ret;
2598 
2599 retry:
2600         if (get_user(uval, uaddr))
2601                 return -EFAULT;
2602         /*
2603          * We release only a lock we actually own:
2604          */
2605         if ((uval & FUTEX_TID_MASK) != vpid)
2606                 return -EPERM;
2607 
2608         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
2609         if (ret)
2610                 return ret;
2611 
2612         hb = hash_futex(&key);
2613         spin_lock(&hb->lock);
2614 
2615         /*
2616          * Check waiters first. We do not trust user space values at
2617          * all and we at least want to know if user space fiddled
2618          * with the futex value instead of blindly unlocking.
2619          */
2620         match = futex_top_waiter(hb, &key);
2621         if (match) {
2622                 ret = wake_futex_pi(uaddr, uval, match, hb);
2623                 /*
2624                  * In case of success wake_futex_pi dropped the hash
2625                  * bucket lock.
2626                  */
2627                 if (!ret)
2628                         goto out_putkey;
2629                 /*
2630                  * The atomic access to the futex value generated a
2631                  * pagefault, so retry the user-access and the wakeup:
2632                  */
2633                 if (ret == -EFAULT)
2634                         goto pi_faulted;
2635                 /*
2636                  * A unconditional UNLOCK_PI op raced against a waiter
2637                  * setting the FUTEX_WAITERS bit. Try again.
2638                  */
2639                 if (ret == -EAGAIN) {
2640                         spin_unlock(&hb->lock);
2641                         put_futex_key(&key);
2642                         goto retry;
2643                 }
2644                 /*
2645                  * wake_futex_pi has detected invalid state. Tell user
2646                  * space.
2647                  */
2648                 goto out_unlock;
2649         }
2650 
2651         /*
2652          * We have no kernel internal state, i.e. no waiters in the
2653          * kernel. Waiters which are about to queue themselves are stuck
2654          * on hb->lock. So we can safely ignore them. We do neither
2655          * preserve the WAITERS bit not the OWNER_DIED one. We are the
2656          * owner.
2657          */
2658         if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))
2659                 goto pi_faulted;
2660 
2661         /*
2662          * If uval has changed, let user space handle it.
2663          */
2664         ret = (curval == uval) ? 0 : -EAGAIN;
2665 
2666 out_unlock:
2667         spin_unlock(&hb->lock);
2668 out_putkey:
2669         put_futex_key(&key);
2670         return ret;
2671 
2672 pi_faulted:
2673         spin_unlock(&hb->lock);
2674         put_futex_key(&key);
2675 
2676         ret = fault_in_user_writeable(uaddr);
2677         if (!ret)
2678                 goto retry;
2679 
2680         return ret;
2681 }
2682 
2683 /**
2684  * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2685  * @hb:         the hash_bucket futex_q was original enqueued on
2686  * @q:          the futex_q woken while waiting to be requeued
2687  * @key2:       the futex_key of the requeue target futex
2688  * @timeout:    the timeout associated with the wait (NULL if none)
2689  *
2690  * Detect if the task was woken on the initial futex as opposed to the requeue
2691  * target futex.  If so, determine if it was a timeout or a signal that caused
2692  * the wakeup and return the appropriate error code to the caller.  Must be
2693  * called with the hb lock held.
2694  *
2695  * Return:
2696  *  0 = no early wakeup detected;
2697  * <0 = -ETIMEDOUT or -ERESTARTNOINTR
2698  */
2699 static inline
2700 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2701                                    struct futex_q *q, union futex_key *key2,
2702                                    struct hrtimer_sleeper *timeout)
2703 {
2704         int ret = 0;
2705 
2706         /*
2707          * With the hb lock held, we avoid races while we process the wakeup.
2708          * We only need to hold hb (and not hb2) to ensure atomicity as the
2709          * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2710          * It can't be requeued from uaddr2 to something else since we don't
2711          * support a PI aware source futex for requeue.
2712          */
2713         if (!match_futex(&q->key, key2)) {
2714                 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2715                 /*
2716                  * We were woken prior to requeue by a timeout or a signal.
2717                  * Unqueue the futex_q and determine which it was.
2718                  */
2719                 plist_del(&q->list, &hb->chain);
2720                 hb_waiters_dec(hb);
2721 
2722                 /* Handle spurious wakeups gracefully */
2723                 ret = -EWOULDBLOCK;
2724                 if (timeout && !timeout->task)
2725                         ret = -ETIMEDOUT;
2726                 else if (signal_pending(current))
2727                         ret = -ERESTARTNOINTR;
2728         }
2729         return ret;
2730 }
2731 
2732 /**
2733  * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2734  * @uaddr:      the futex we initially wait on (non-pi)
2735  * @flags:      futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
2736  *              the same type, no requeueing from private to shared, etc.
2737  * @val:        the expected value of uaddr
2738  * @abs_time:   absolute timeout
2739  * @bitset:     32 bit wakeup bitset set by userspace, defaults to all
2740  * @uaddr2:     the pi futex we will take prior to returning to user-space
2741  *
2742  * The caller will wait on uaddr and will be requeued by futex_requeue() to
2743  * uaddr2 which must be PI aware and unique from uaddr.  Normal wakeup will wake
2744  * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
2745  * userspace.  This ensures the rt_mutex maintains an owner when it has waiters;
2746  * without one, the pi logic would not know which task to boost/deboost, if
2747  * there was a need to.
2748  *
2749  * We call schedule in futex_wait_queue_me() when we enqueue and return there
2750  * via the following--
2751  * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2752  * 2) wakeup on uaddr2 after a requeue
2753  * 3) signal
2754  * 4) timeout
2755  *
2756  * If 3, cleanup and return -ERESTARTNOINTR.
2757  *
2758  * If 2, we may then block on trying to take the rt_mutex and return via:
2759  * 5) successful lock
2760  * 6) signal
2761  * 7) timeout
2762  * 8) other lock acquisition failure
2763  *
2764  * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
2765  *
2766  * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2767  *
2768  * Return:
2769  *  0 - On success;
2770  * <0 - On error
2771  */
2772 static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
2773                                  u32 val, ktime_t *abs_time, u32 bitset,
2774                                  u32 __user *uaddr2)
2775 {
2776         struct hrtimer_sleeper timeout, *to = NULL;
2777         struct rt_mutex_waiter rt_waiter;
2778         struct rt_mutex *pi_mutex = NULL;
2779         struct futex_hash_bucket *hb;
2780         union futex_key key2 = FUTEX_KEY_INIT;
2781         struct futex_q q = futex_q_init;
2782         int res, ret;
2783 
2784         if (uaddr == uaddr2)
2785                 return -EINVAL;
2786 
2787         if (!bitset)
2788                 return -EINVAL;
2789 
2790         if (abs_time) {
2791                 to = &timeout;
2792                 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2793                                       CLOCK_REALTIME : CLOCK_MONOTONIC,
2794                                       HRTIMER_MODE_ABS);
2795                 hrtimer_init_sleeper(to, current);
2796                 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2797                                              current->timer_slack_ns);
2798         }
2799 
2800         /*
2801          * The waiter is allocated on our stack, manipulated by the requeue
2802          * code while we sleep on uaddr.
2803          */
2804         debug_rt_mutex_init_waiter(&rt_waiter);
2805         RB_CLEAR_NODE(&rt_waiter.pi_tree_entry);
2806         RB_CLEAR_NODE(&rt_waiter.tree_entry);
2807         rt_waiter.task = NULL;
2808 
2809         ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
2810         if (unlikely(ret != 0))
2811                 goto out;
2812 
2813         q.bitset = bitset;
2814         q.rt_waiter = &rt_waiter;
2815         q.requeue_pi_key = &key2;
2816 
2817         /*
2818          * Prepare to wait on uaddr. On success, increments q.key (key1) ref
2819          * count.
2820          */
2821         ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2822         if (ret)
2823                 goto out_key2;
2824 
2825         /*
2826          * The check above which compares uaddrs is not sufficient for
2827          * shared futexes. We need to compare the keys:
2828          */
2829         if (match_futex(&q.key, &key2)) {
2830                 queue_unlock(hb);
2831                 ret = -EINVAL;
2832                 goto out_put_keys;
2833         }
2834 
2835         /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2836         futex_wait_queue_me(hb, &q, to);
2837 
2838         spin_lock(&hb->lock);
2839         ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2840         spin_unlock(&hb->lock);
2841         if (ret)
2842                 goto out_put_keys;
2843 
2844         /*
2845          * In order for us to be here, we know our q.key == key2, and since
2846          * we took the hb->lock above, we also know that futex_requeue() has
2847          * completed and we no longer have to concern ourselves with a wakeup
2848          * race with the atomic proxy lock acquisition by the requeue code. The
2849          * futex_requeue dropped our key1 reference and incremented our key2
2850          * reference count.
2851          */
2852 
2853         /* Check if the requeue code acquired the second futex for us. */
2854         if (!q.rt_waiter) {
2855                 /*
2856                  * Got the lock. We might not be the anticipated owner if we
2857                  * did a lock-steal - fix up the PI-state in that case.
2858                  */
2859                 if (q.pi_state && (q.pi_state->owner != current)) {
2860                         spin_lock(q.lock_ptr);
2861                         ret = fixup_pi_state_owner(uaddr2, &q, current);
2862                         /*
2863                          * Drop the reference to the pi state which
2864                          * the requeue_pi() code acquired for us.
2865                          */
2866                         put_pi_state(q.pi_state);
2867                         spin_unlock(q.lock_ptr);
2868                 }
2869         } else {
2870                 /*
2871                  * We have been woken up by futex_unlock_pi(), a timeout, or a
2872                  * signal.  futex_unlock_pi() will not destroy the lock_ptr nor
2873                  * the pi_state.
2874                  */
2875                 WARN_ON(!q.pi_state);
2876                 pi_mutex = &q.pi_state->pi_mutex;
2877                 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter);
2878                 debug_rt_mutex_free_waiter(&rt_waiter);
2879 
2880                 spin_lock(q.lock_ptr);
2881                 /*
2882                  * Fixup the pi_state owner and possibly acquire the lock if we
2883                  * haven't already.
2884                  */
2885                 res = fixup_owner(uaddr2, &q, !ret);
2886                 /*
2887                  * If fixup_owner() returned an error, proprogate that.  If it
2888                  * acquired the lock, clear -ETIMEDOUT or -EINTR.
2889                  */
2890                 if (res)
2891                         ret = (res < 0) ? res : 0;
2892 
2893                 /* Unqueue and drop the lock. */
2894                 unqueue_me_pi(&q);
2895         }
2896 
2897         /*
2898          * If fixup_pi_state_owner() faulted and was unable to handle the
2899          * fault, unlock the rt_mutex and return the fault to userspace.
2900          */
2901         if (ret == -EFAULT) {
2902                 if (pi_mutex && rt_mutex_owner(pi_mutex) == current)
2903                         rt_mutex_unlock(pi_mutex);
2904         } else if (ret == -EINTR) {
2905                 /*
2906                  * We've already been requeued, but cannot restart by calling
2907                  * futex_lock_pi() directly. We could restart this syscall, but
2908                  * it would detect that the user space "val" changed and return
2909                  * -EWOULDBLOCK.  Save the overhead of the restart and return
2910                  * -EWOULDBLOCK directly.
2911                  */
2912                 ret = -EWOULDBLOCK;
2913         }
2914 
2915 out_put_keys:
2916         put_futex_key(&q.key);
2917 out_key2:
2918         put_futex_key(&key2);
2919 
2920 out:
2921         if (to) {
2922                 hrtimer_cancel(&to->timer);
2923                 destroy_hrtimer_on_stack(&to->timer);
2924         }
2925         return ret;
2926 }
2927 
2928 /*
2929  * Support for robust futexes: the kernel cleans up held futexes at
2930  * thread exit time.
2931  *
2932  * Implementation: user-space maintains a per-thread list of locks it
2933  * is holding. Upon do_exit(), the kernel carefully walks this list,
2934  * and marks all locks that are owned by this thread with the
2935  * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2936  * always manipulated with the lock held, so the list is private and
2937  * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2938  * field, to allow the kernel to clean up if the thread dies after
2939  * acquiring the lock, but just before it could have added itself to
2940  * the list. There can only be one such pending lock.
2941  */
2942 
2943 /**
2944  * sys_set_robust_list() - Set the robust-futex list head of a task
2945  * @head:       pointer to the list-head
2946  * @len:        length of the list-head, as userspace expects
2947  */
2948 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2949                 size_t, len)
2950 {
2951         if (!futex_cmpxchg_enabled)
2952                 return -ENOSYS;
2953         /*
2954          * The kernel knows only one size for now:
2955          */
2956         if (unlikely(len != sizeof(*head)))
2957                 return -EINVAL;
2958 
2959         current->robust_list = head;
2960 
2961         return 0;
2962 }
2963 
2964 /**
2965  * sys_get_robust_list() - Get the robust-futex list head of a task
2966  * @pid:        pid of the process [zero for current task]
2967  * @head_ptr:   pointer to a list-head pointer, the kernel fills it in
2968  * @len_ptr:    pointer to a length field, the kernel fills in the header size
2969  */
2970 SYSCALL_DEFINE3(get_robust_list, int, pid,
2971                 struct robust_list_head __user * __user *, head_ptr,
2972                 size_t __user *, len_ptr)
2973 {
2974         struct robust_list_head __user *head;
2975         unsigned long ret;
2976         struct task_struct *p;
2977 
2978         if (!futex_cmpxchg_enabled)
2979                 return -ENOSYS;
2980 
2981         rcu_read_lock();
2982 
2983         ret = -ESRCH;
2984         if (!pid)
2985                 p = current;
2986         else {
2987                 p = find_task_by_vpid(pid);
2988                 if (!p)
2989                         goto err_unlock;
2990         }
2991 
2992         ret = -EPERM;
2993         if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
2994                 goto err_unlock;
2995 
2996         head = p->robust_list;
2997         rcu_read_unlock();
2998 
2999         if (put_user(sizeof(*head), len_ptr))
3000                 return -EFAULT;
3001         return put_user(head, head_ptr);
3002 
3003 err_unlock:
3004         rcu_read_unlock();
3005 
3006         return ret;
3007 }
3008 
3009 /*
3010  * Process a futex-list entry, check whether it's owned by the
3011  * dying task, and do notification if so:
3012  */
3013 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
3014 {
3015         u32 uval, uninitialized_var(nval), mval;
3016 
3017 retry:
3018         if (get_user(uval, uaddr))
3019                 return -1;
3020 
3021         if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
3022                 /*
3023                  * Ok, this dying thread is truly holding a futex
3024                  * of interest. Set the OWNER_DIED bit atomically
3025                  * via cmpxchg, and if the value had FUTEX_WAITERS
3026                  * set, wake up a waiter (if any). (We have to do a
3027                  * futex_wake() even if OWNER_DIED is already set -
3028                  * to handle the rare but possible case of recursive
3029                  * thread-death.) The rest of the cleanup is done in
3030                  * userspace.
3031                  */
3032                 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
3033                 /*
3034                  * We are not holding a lock here, but we want to have
3035                  * the pagefault_disable/enable() protection because
3036                  * we want to handle the fault gracefully. If the
3037                  * access fails we try to fault in the futex with R/W
3038                  * verification via get_user_pages. get_user() above
3039                  * does not guarantee R/W access. If that fails we
3040                  * give up and leave the futex locked.
3041                  */
3042                 if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
3043                         if (fault_in_user_writeable(uaddr))
3044                                 return -1;
3045                         goto retry;
3046                 }
3047                 if (nval != uval)
3048                         goto retry;
3049 
3050                 /*
3051                  * Wake robust non-PI futexes here. The wakeup of
3052                  * PI futexes happens in exit_pi_state():
3053                  */
3054                 if (!pi && (uval & FUTEX_WAITERS))
3055                         futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
3056         }
3057         return 0;
3058 }
3059 
3060 /*
3061  * Fetch a robust-list pointer. Bit 0 signals PI futexes:
3062  */
3063 static inline int fetch_robust_entry(struct robust_list __user **entry,
3064                                      struct robust_list __user * __user *head,
3065                                      unsigned int *pi)
3066 {
3067         unsigned long uentry;
3068 
3069         if (get_user(uentry, (unsigned long __user *)head))
3070                 return -EFAULT;
3071 
3072         *entry = (void __user *)(uentry & ~1UL);
3073         *pi = uentry & 1;
3074 
3075         return 0;
3076 }
3077 
3078 /*
3079  * Walk curr->robust_list (very carefully, it's a userspace list!)
3080  * and mark any locks found there dead, and notify any waiters.
3081  *
3082  * We silently return on any sign of list-walking problem.
3083  */
3084 void exit_robust_list(struct task_struct *curr)
3085 {
3086         struct robust_list_head __user *head = curr->robust_list;
3087         struct robust_list __user *entry, *next_entry, *pending;
3088         unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
3089         unsigned int uninitialized_var(next_pi);
3090         unsigned long futex_offset;
3091         int rc;
3092 
3093         if (!futex_cmpxchg_enabled)
3094                 return;
3095 
3096         /*
3097          * Fetch the list head (which was registered earlier, via
3098          * sys_set_robust_list()):
3099          */
3100         if (fetch_robust_entry(&entry, &head->list.next, &pi))
3101                 return;
3102         /*
3103          * Fetch the relative futex offset:
3104          */
3105         if (get_user(futex_offset, &head->futex_offset))
3106                 return;
3107         /*
3108          * Fetch any possibly pending lock-add first, and handle it
3109          * if it exists:
3110          */
3111         if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
3112                 return;
3113 
3114         next_entry = NULL;      /* avoid warning with gcc */
3115         while (entry != &head->list) {
3116                 /*
3117                  * Fetch the next entry in the list before calling
3118                  * handle_futex_death:
3119                  */
3120                 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
3121                 /*
3122                  * A pending lock might already be on the list, so
3123                  * don't process it twice:
3124                  */
3125                 if (entry != pending)
3126                         if (handle_futex_death((void __user *)entry + futex_offset,
3127                                                 curr, pi))
3128                                 return;
3129                 if (rc)
3130                         return;
3131                 entry = next_entry;
3132                 pi = next_pi;
3133                 /*
3134                  * Avoid excessively long or circular lists:
3135                  */
3136                 if (!--limit)
3137                         break;
3138 
3139                 cond_resched();
3140         }
3141 
3142         if (pending)
3143                 handle_futex_death((void __user *)pending + futex_offset,
3144                                    curr, pip);
3145 }
3146 
3147 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
3148                 u32 __user *uaddr2, u32 val2, u32 val3)
3149 {
3150         int cmd = op & FUTEX_CMD_MASK;
3151         unsigned int flags = 0;
3152 
3153         if (!(op & FUTEX_PRIVATE_FLAG))
3154                 flags |= FLAGS_SHARED;
3155 
3156         if (op & FUTEX_CLOCK_REALTIME) {
3157                 flags |= FLAGS_CLOCKRT;
3158                 if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \
3159                     cmd != FUTEX_WAIT_REQUEUE_PI)
3160                         return -ENOSYS;
3161         }
3162 
3163         switch (cmd) {
3164         case FUTEX_LOCK_PI:
3165         case FUTEX_UNLOCK_PI:
3166         case FUTEX_TRYLOCK_PI:
3167         case FUTEX_WAIT_REQUEUE_PI:
3168         case FUTEX_CMP_REQUEUE_PI:
3169                 if (!futex_cmpxchg_enabled)
3170                         return -ENOSYS;
3171         }
3172 
3173         switch (cmd) {
3174         case FUTEX_WAIT:
3175                 val3 = FUTEX_BITSET_MATCH_ANY;
3176         case FUTEX_WAIT_BITSET:
3177                 return futex_wait(uaddr, flags, val, timeout, val3);
3178         case FUTEX_WAKE:
3179                 val3 = FUTEX_BITSET_MATCH_ANY;
3180         case FUTEX_WAKE_BITSET:
3181                 return futex_wake(uaddr, flags, val, val3);
3182         case FUTEX_REQUEUE:
3183                 return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
3184         case FUTEX_CMP_REQUEUE:
3185                 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
3186         case FUTEX_WAKE_OP:
3187                 return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
3188         case FUTEX_LOCK_PI:
3189                 return futex_lock_pi(uaddr, flags, timeout, 0);
3190         case FUTEX_UNLOCK_PI:
3191                 return futex_unlock_pi(uaddr, flags);
3192         case FUTEX_TRYLOCK_PI:
3193                 return futex_lock_pi(uaddr, flags, NULL, 1);
3194         case FUTEX_WAIT_REQUEUE_PI:
3195                 val3 = FUTEX_BITSET_MATCH_ANY;
3196                 return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
3197                                              uaddr2);
3198         case FUTEX_CMP_REQUEUE_PI:
3199                 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
3200         }
3201         return -ENOSYS;
3202 }
3203 
3204 
3205 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
3206                 struct timespec __user *, utime, u32 __user *, uaddr2,
3207                 u32, val3)
3208 {
3209         struct timespec ts;
3210         ktime_t t, *tp = NULL;
3211         u32 val2 = 0;
3212         int cmd = op & FUTEX_CMD_MASK;
3213 
3214         if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
3215                       cmd == FUTEX_WAIT_BITSET ||
3216                       cmd == FUTEX_WAIT_REQUEUE_PI)) {
3217                 if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
3218                         return -EFAULT;
3219                 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
3220                         return -EFAULT;
3221                 if (!timespec_valid(&ts))
3222                         return -EINVAL;
3223 
3224                 t = timespec_to_ktime(ts);
3225                 if (cmd == FUTEX_WAIT)
3226                         t = ktime_add_safe(ktime_get(), t);
3227                 tp = &t;
3228         }
3229         /*
3230          * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
3231          * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
3232          */
3233         if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
3234             cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
3235                 val2 = (u32) (unsigned long) utime;
3236 
3237         return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
3238 }
3239 
3240 static void __init futex_detect_cmpxchg(void)
3241 {
3242 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
3243         u32 curval;
3244 
3245         /*
3246          * This will fail and we want it. Some arch implementations do
3247          * runtime detection of the futex_atomic_cmpxchg_inatomic()
3248          * functionality. We want to know that before we call in any
3249          * of the complex code paths. Also we want to prevent
3250          * registration of robust lists in that case. NULL is
3251          * guaranteed to fault and we get -EFAULT on functional
3252          * implementation, the non-functional ones will return
3253          * -ENOSYS.
3254          */
3255         if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
3256                 futex_cmpxchg_enabled = 1;
3257 #endif
3258 }
3259 
3260 static int __init futex_init(void)
3261 {
3262         unsigned int futex_shift;
3263         unsigned long i;
3264 
3265 #if CONFIG_BASE_SMALL
3266         futex_hashsize = 16;
3267 #else
3268         futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
3269 #endif
3270 
3271         futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
3272                                                futex_hashsize, 0,
3273                                                futex_hashsize < 256 ? HASH_SMALL : 0,
3274                                                &futex_shift, NULL,
3275                                                futex_hashsize, futex_hashsize);
3276         futex_hashsize = 1UL << futex_shift;
3277 
3278         futex_detect_cmpxchg();
3279 
3280         for (i = 0; i < futex_hashsize; i++) {
3281                 atomic_set(&futex_queues[i].waiters, 0);
3282                 plist_head_init(&futex_queues[i].chain);
3283                 spin_lock_init(&futex_queues[i].lock);
3284         }
3285 
3286         return 0;
3287 }
3288 __initcall(futex_init);
3289 

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