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Linux/ipc/sem.c

  1 /*
  2  * linux/ipc/sem.c
  3  * Copyright (C) 1992 Krishna Balasubramanian
  4  * Copyright (C) 1995 Eric Schenk, Bruno Haible
  5  *
  6  * /proc/sysvipc/sem support (c) 1999 Dragos Acostachioaie <dragos@iname.com>
  7  *
  8  * SMP-threaded, sysctl's added
  9  * (c) 1999 Manfred Spraul <manfred@colorfullife.com>
 10  * Enforced range limit on SEM_UNDO
 11  * (c) 2001 Red Hat Inc
 12  * Lockless wakeup
 13  * (c) 2003 Manfred Spraul <manfred@colorfullife.com>
 14  * Further wakeup optimizations, documentation
 15  * (c) 2010 Manfred Spraul <manfred@colorfullife.com>
 16  *
 17  * support for audit of ipc object properties and permission changes
 18  * Dustin Kirkland <dustin.kirkland@us.ibm.com>
 19  *
 20  * namespaces support
 21  * OpenVZ, SWsoft Inc.
 22  * Pavel Emelianov <xemul@openvz.org>
 23  *
 24  * Implementation notes: (May 2010)
 25  * This file implements System V semaphores.
 26  *
 27  * User space visible behavior:
 28  * - FIFO ordering for semop() operations (just FIFO, not starvation
 29  *   protection)
 30  * - multiple semaphore operations that alter the same semaphore in
 31  *   one semop() are handled.
 32  * - sem_ctime (time of last semctl()) is updated in the IPC_SET, SETVAL and
 33  *   SETALL calls.
 34  * - two Linux specific semctl() commands: SEM_STAT, SEM_INFO.
 35  * - undo adjustments at process exit are limited to 0..SEMVMX.
 36  * - namespace are supported.
 37  * - SEMMSL, SEMMNS, SEMOPM and SEMMNI can be configured at runtine by writing
 38  *   to /proc/sys/kernel/sem.
 39  * - statistics about the usage are reported in /proc/sysvipc/sem.
 40  *
 41  * Internals:
 42  * - scalability:
 43  *   - all global variables are read-mostly.
 44  *   - semop() calls and semctl(RMID) are synchronized by RCU.
 45  *   - most operations do write operations (actually: spin_lock calls) to
 46  *     the per-semaphore array structure.
 47  *   Thus: Perfect SMP scaling between independent semaphore arrays.
 48  *         If multiple semaphores in one array are used, then cache line
 49  *         trashing on the semaphore array spinlock will limit the scaling.
 50  * - semncnt and semzcnt are calculated on demand in count_semcnt()
 51  * - the task that performs a successful semop() scans the list of all
 52  *   sleeping tasks and completes any pending operations that can be fulfilled.
 53  *   Semaphores are actively given to waiting tasks (necessary for FIFO).
 54  *   (see update_queue())
 55  * - To improve the scalability, the actual wake-up calls are performed after
 56  *   dropping all locks. (see wake_up_sem_queue_prepare(),
 57  *   wake_up_sem_queue_do())
 58  * - All work is done by the waker, the woken up task does not have to do
 59  *   anything - not even acquiring a lock or dropping a refcount.
 60  * - A woken up task may not even touch the semaphore array anymore, it may
 61  *   have been destroyed already by a semctl(RMID).
 62  * - The synchronizations between wake-ups due to a timeout/signal and a
 63  *   wake-up due to a completed semaphore operation is achieved by using an
 64  *   intermediate state (IN_WAKEUP).
 65  * - UNDO values are stored in an array (one per process and per
 66  *   semaphore array, lazily allocated). For backwards compatibility, multiple
 67  *   modes for the UNDO variables are supported (per process, per thread)
 68  *   (see copy_semundo, CLONE_SYSVSEM)
 69  * - There are two lists of the pending operations: a per-array list
 70  *   and per-semaphore list (stored in the array). This allows to achieve FIFO
 71  *   ordering without always scanning all pending operations.
 72  *   The worst-case behavior is nevertheless O(N^2) for N wakeups.
 73  */
 74 
 75 #include <linux/slab.h>
 76 #include <linux/spinlock.h>
 77 #include <linux/init.h>
 78 #include <linux/proc_fs.h>
 79 #include <linux/time.h>
 80 #include <linux/security.h>
 81 #include <linux/syscalls.h>
 82 #include <linux/audit.h>
 83 #include <linux/capability.h>
 84 #include <linux/seq_file.h>
 85 #include <linux/rwsem.h>
 86 #include <linux/nsproxy.h>
 87 #include <linux/ipc_namespace.h>
 88 
 89 #include <linux/uaccess.h>
 90 #include "util.h"
 91 
 92 /* One semaphore structure for each semaphore in the system. */
 93 struct sem {
 94         int     semval;         /* current value */
 95         /*
 96          * PID of the process that last modified the semaphore. For
 97          * Linux, specifically these are:
 98          *  - semop
 99          *  - semctl, via SETVAL and SETALL.
100          *  - at task exit when performing undo adjustments (see exit_sem).
101          */
102         int     sempid;
103         spinlock_t      lock;   /* spinlock for fine-grained semtimedop */
104         struct list_head pending_alter; /* pending single-sop operations */
105                                         /* that alter the semaphore */
106         struct list_head pending_const; /* pending single-sop operations */
107                                         /* that do not alter the semaphore*/
108         time_t  sem_otime;      /* candidate for sem_otime */
109 } ____cacheline_aligned_in_smp;
110 
111 /* One queue for each sleeping process in the system. */
112 struct sem_queue {
113         struct list_head        list;    /* queue of pending operations */
114         struct task_struct      *sleeper; /* this process */
115         struct sem_undo         *undo;   /* undo structure */
116         int                     pid;     /* process id of requesting process */
117         int                     status;  /* completion status of operation */
118         struct sembuf           *sops;   /* array of pending operations */
119         struct sembuf           *blocking; /* the operation that blocked */
120         int                     nsops;   /* number of operations */
121         int                     alter;   /* does *sops alter the array? */
122 };
123 
124 /* Each task has a list of undo requests. They are executed automatically
125  * when the process exits.
126  */
127 struct sem_undo {
128         struct list_head        list_proc;      /* per-process list: *
129                                                  * all undos from one process
130                                                  * rcu protected */
131         struct rcu_head         rcu;            /* rcu struct for sem_undo */
132         struct sem_undo_list    *ulp;           /* back ptr to sem_undo_list */
133         struct list_head        list_id;        /* per semaphore array list:
134                                                  * all undos for one array */
135         int                     semid;          /* semaphore set identifier */
136         short                   *semadj;        /* array of adjustments */
137                                                 /* one per semaphore */
138 };
139 
140 /* sem_undo_list controls shared access to the list of sem_undo structures
141  * that may be shared among all a CLONE_SYSVSEM task group.
142  */
143 struct sem_undo_list {
144         atomic_t                refcnt;
145         spinlock_t              lock;
146         struct list_head        list_proc;
147 };
148 
149 
150 #define sem_ids(ns)     ((ns)->ids[IPC_SEM_IDS])
151 
152 #define sem_checkid(sma, semid) ipc_checkid(&sma->sem_perm, semid)
153 
154 static int newary(struct ipc_namespace *, struct ipc_params *);
155 static void freeary(struct ipc_namespace *, struct kern_ipc_perm *);
156 #ifdef CONFIG_PROC_FS
157 static int sysvipc_sem_proc_show(struct seq_file *s, void *it);
158 #endif
159 
160 #define SEMMSL_FAST     256 /* 512 bytes on stack */
161 #define SEMOPM_FAST     64  /* ~ 372 bytes on stack */
162 
163 /*
164  * Locking:
165  *      sem_undo.id_next,
166  *      sem_array.complex_count,
167  *      sem_array.pending{_alter,_cont},
168  *      sem_array.sem_undo: global sem_lock() for read/write
169  *      sem_undo.proc_next: only "current" is allowed to read/write that field.
170  *
171  *      sem_array.sem_base[i].pending_{const,alter}:
172  *              global or semaphore sem_lock() for read/write
173  */
174 
175 #define sc_semmsl       sem_ctls[0]
176 #define sc_semmns       sem_ctls[1]
177 #define sc_semopm       sem_ctls[2]
178 #define sc_semmni       sem_ctls[3]
179 
180 void sem_init_ns(struct ipc_namespace *ns)
181 {
182         ns->sc_semmsl = SEMMSL;
183         ns->sc_semmns = SEMMNS;
184         ns->sc_semopm = SEMOPM;
185         ns->sc_semmni = SEMMNI;
186         ns->used_sems = 0;
187         ipc_init_ids(&ns->ids[IPC_SEM_IDS]);
188 }
189 
190 #ifdef CONFIG_IPC_NS
191 void sem_exit_ns(struct ipc_namespace *ns)
192 {
193         free_ipcs(ns, &sem_ids(ns), freeary);
194         idr_destroy(&ns->ids[IPC_SEM_IDS].ipcs_idr);
195 }
196 #endif
197 
198 void __init sem_init(void)
199 {
200         sem_init_ns(&init_ipc_ns);
201         ipc_init_proc_interface("sysvipc/sem",
202                                 "       key      semid perms      nsems   uid   gid  cuid  cgid      otime      ctime\n",
203                                 IPC_SEM_IDS, sysvipc_sem_proc_show);
204 }
205 
206 /**
207  * unmerge_queues - unmerge queues, if possible.
208  * @sma: semaphore array
209  *
210  * The function unmerges the wait queues if complex_count is 0.
211  * It must be called prior to dropping the global semaphore array lock.
212  */
213 static void unmerge_queues(struct sem_array *sma)
214 {
215         struct sem_queue *q, *tq;
216 
217         /* complex operations still around? */
218         if (sma->complex_count)
219                 return;
220         /*
221          * We will switch back to simple mode.
222          * Move all pending operation back into the per-semaphore
223          * queues.
224          */
225         list_for_each_entry_safe(q, tq, &sma->pending_alter, list) {
226                 struct sem *curr;
227                 curr = &sma->sem_base[q->sops[0].sem_num];
228 
229                 list_add_tail(&q->list, &curr->pending_alter);
230         }
231         INIT_LIST_HEAD(&sma->pending_alter);
232 }
233 
234 /**
235  * merge_queues - merge single semop queues into global queue
236  * @sma: semaphore array
237  *
238  * This function merges all per-semaphore queues into the global queue.
239  * It is necessary to achieve FIFO ordering for the pending single-sop
240  * operations when a multi-semop operation must sleep.
241  * Only the alter operations must be moved, the const operations can stay.
242  */
243 static void merge_queues(struct sem_array *sma)
244 {
245         int i;
246         for (i = 0; i < sma->sem_nsems; i++) {
247                 struct sem *sem = sma->sem_base + i;
248 
249                 list_splice_init(&sem->pending_alter, &sma->pending_alter);
250         }
251 }
252 
253 static void sem_rcu_free(struct rcu_head *head)
254 {
255         struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu);
256         struct sem_array *sma = ipc_rcu_to_struct(p);
257 
258         security_sem_free(sma);
259         ipc_rcu_free(head);
260 }
261 
262 /*
263  * spin_unlock_wait() and !spin_is_locked() are not memory barriers, they
264  * are only control barriers.
265  * The code must pair with spin_unlock(&sem->lock) or
266  * spin_unlock(&sem_perm.lock), thus just the control barrier is insufficient.
267  *
268  * smp_rmb() is sufficient, as writes cannot pass the control barrier.
269  */
270 #define ipc_smp_acquire__after_spin_is_unlocked()       smp_rmb()
271 
272 /*
273  * Wait until all currently ongoing simple ops have completed.
274  * Caller must own sem_perm.lock.
275  * New simple ops cannot start, because simple ops first check
276  * that sem_perm.lock is free.
277  * that a) sem_perm.lock is free and b) complex_count is 0.
278  */
279 static void sem_wait_array(struct sem_array *sma)
280 {
281         int i;
282         struct sem *sem;
283 
284         if (sma->complex_count)  {
285                 /* The thread that increased sma->complex_count waited on
286                  * all sem->lock locks. Thus we don't need to wait again.
287                  */
288                 return;
289         }
290 
291         for (i = 0; i < sma->sem_nsems; i++) {
292                 sem = sma->sem_base + i;
293                 spin_unlock_wait(&sem->lock);
294         }
295         ipc_smp_acquire__after_spin_is_unlocked();
296 }
297 
298 /*
299  * If the request contains only one semaphore operation, and there are
300  * no complex transactions pending, lock only the semaphore involved.
301  * Otherwise, lock the entire semaphore array, since we either have
302  * multiple semaphores in our own semops, or we need to look at
303  * semaphores from other pending complex operations.
304  */
305 static inline int sem_lock(struct sem_array *sma, struct sembuf *sops,
306                               int nsops)
307 {
308         struct sem *sem;
309 
310         if (nsops != 1) {
311                 /* Complex operation - acquire a full lock */
312                 ipc_lock_object(&sma->sem_perm);
313 
314                 /* And wait until all simple ops that are processed
315                  * right now have dropped their locks.
316                  */
317                 sem_wait_array(sma);
318                 return -1;
319         }
320 
321         /*
322          * Only one semaphore affected - try to optimize locking.
323          * The rules are:
324          * - optimized locking is possible if no complex operation
325          *   is either enqueued or processed right now.
326          * - The test for enqueued complex ops is simple:
327          *      sma->complex_count != 0
328          * - Testing for complex ops that are processed right now is
329          *   a bit more difficult. Complex ops acquire the full lock
330          *   and first wait that the running simple ops have completed.
331          *   (see above)
332          *   Thus: If we own a simple lock and the global lock is free
333          *      and complex_count is now 0, then it will stay 0 and
334          *      thus just locking sem->lock is sufficient.
335          */
336         sem = sma->sem_base + sops->sem_num;
337 
338         if (sma->complex_count == 0) {
339                 /*
340                  * It appears that no complex operation is around.
341                  * Acquire the per-semaphore lock.
342                  */
343                 spin_lock(&sem->lock);
344 
345                 /* Then check that the global lock is free */
346                 if (!spin_is_locked(&sma->sem_perm.lock)) {
347                         /*
348                          * We need a memory barrier with acquire semantics,
349                          * otherwise we can race with another thread that does:
350                          *      complex_count++;
351                          *      spin_unlock(sem_perm.lock);
352                          */
353                         ipc_smp_acquire__after_spin_is_unlocked();
354 
355                         /*
356                          * Now repeat the test of complex_count:
357                          * It can't change anymore until we drop sem->lock.
358                          * Thus: if is now 0, then it will stay 0.
359                          */
360                         if (sma->complex_count == 0) {
361                                 /* fast path successful! */
362                                 return sops->sem_num;
363                         }
364                 }
365                 spin_unlock(&sem->lock);
366         }
367 
368         /* slow path: acquire the full lock */
369         ipc_lock_object(&sma->sem_perm);
370 
371         if (sma->complex_count == 0) {
372                 /* False alarm:
373                  * There is no complex operation, thus we can switch
374                  * back to the fast path.
375                  */
376                 spin_lock(&sem->lock);
377                 ipc_unlock_object(&sma->sem_perm);
378                 return sops->sem_num;
379         } else {
380                 /* Not a false alarm, thus complete the sequence for a
381                  * full lock.
382                  */
383                 sem_wait_array(sma);
384                 return -1;
385         }
386 }
387 
388 static inline void sem_unlock(struct sem_array *sma, int locknum)
389 {
390         if (locknum == -1) {
391                 unmerge_queues(sma);
392                 ipc_unlock_object(&sma->sem_perm);
393         } else {
394                 struct sem *sem = sma->sem_base + locknum;
395                 spin_unlock(&sem->lock);
396         }
397 }
398 
399 /*
400  * sem_lock_(check_) routines are called in the paths where the rwsem
401  * is not held.
402  *
403  * The caller holds the RCU read lock.
404  */
405 static inline struct sem_array *sem_obtain_lock(struct ipc_namespace *ns,
406                         int id, struct sembuf *sops, int nsops, int *locknum)
407 {
408         struct kern_ipc_perm *ipcp;
409         struct sem_array *sma;
410 
411         ipcp = ipc_obtain_object_idr(&sem_ids(ns), id);
412         if (IS_ERR(ipcp))
413                 return ERR_CAST(ipcp);
414 
415         sma = container_of(ipcp, struct sem_array, sem_perm);
416         *locknum = sem_lock(sma, sops, nsops);
417 
418         /* ipc_rmid() may have already freed the ID while sem_lock
419          * was spinning: verify that the structure is still valid
420          */
421         if (ipc_valid_object(ipcp))
422                 return container_of(ipcp, struct sem_array, sem_perm);
423 
424         sem_unlock(sma, *locknum);
425         return ERR_PTR(-EINVAL);
426 }
427 
428 static inline struct sem_array *sem_obtain_object(struct ipc_namespace *ns, int id)
429 {
430         struct kern_ipc_perm *ipcp = ipc_obtain_object_idr(&sem_ids(ns), id);
431 
432         if (IS_ERR(ipcp))
433                 return ERR_CAST(ipcp);
434 
435         return container_of(ipcp, struct sem_array, sem_perm);
436 }
437 
438 static inline struct sem_array *sem_obtain_object_check(struct ipc_namespace *ns,
439                                                         int id)
440 {
441         struct kern_ipc_perm *ipcp = ipc_obtain_object_check(&sem_ids(ns), id);
442 
443         if (IS_ERR(ipcp))
444                 return ERR_CAST(ipcp);
445 
446         return container_of(ipcp, struct sem_array, sem_perm);
447 }
448 
449 static inline void sem_lock_and_putref(struct sem_array *sma)
450 {
451         sem_lock(sma, NULL, -1);
452         ipc_rcu_putref(sma, ipc_rcu_free);
453 }
454 
455 static inline void sem_rmid(struct ipc_namespace *ns, struct sem_array *s)
456 {
457         ipc_rmid(&sem_ids(ns), &s->sem_perm);
458 }
459 
460 /*
461  * Lockless wakeup algorithm:
462  * Without the check/retry algorithm a lockless wakeup is possible:
463  * - queue.status is initialized to -EINTR before blocking.
464  * - wakeup is performed by
465  *      * unlinking the queue entry from the pending list
466  *      * setting queue.status to IN_WAKEUP
467  *        This is the notification for the blocked thread that a
468  *        result value is imminent.
469  *      * call wake_up_process
470  *      * set queue.status to the final value.
471  * - the previously blocked thread checks queue.status:
472  *      * if it's IN_WAKEUP, then it must wait until the value changes
473  *      * if it's not -EINTR, then the operation was completed by
474  *        update_queue. semtimedop can return queue.status without
475  *        performing any operation on the sem array.
476  *      * otherwise it must acquire the spinlock and check what's up.
477  *
478  * The two-stage algorithm is necessary to protect against the following
479  * races:
480  * - if queue.status is set after wake_up_process, then the woken up idle
481  *   thread could race forward and try (and fail) to acquire sma->lock
482  *   before update_queue had a chance to set queue.status
483  * - if queue.status is written before wake_up_process and if the
484  *   blocked process is woken up by a signal between writing
485  *   queue.status and the wake_up_process, then the woken up
486  *   process could return from semtimedop and die by calling
487  *   sys_exit before wake_up_process is called. Then wake_up_process
488  *   will oops, because the task structure is already invalid.
489  *   (yes, this happened on s390 with sysv msg).
490  *
491  */
492 #define IN_WAKEUP       1
493 
494 /**
495  * newary - Create a new semaphore set
496  * @ns: namespace
497  * @params: ptr to the structure that contains key, semflg and nsems
498  *
499  * Called with sem_ids.rwsem held (as a writer)
500  */
501 static int newary(struct ipc_namespace *ns, struct ipc_params *params)
502 {
503         int id;
504         int retval;
505         struct sem_array *sma;
506         int size;
507         key_t key = params->key;
508         int nsems = params->u.nsems;
509         int semflg = params->flg;
510         int i;
511 
512         if (!nsems)
513                 return -EINVAL;
514         if (ns->used_sems + nsems > ns->sc_semmns)
515                 return -ENOSPC;
516 
517         size = sizeof(*sma) + nsems * sizeof(struct sem);
518         sma = ipc_rcu_alloc(size);
519         if (!sma)
520                 return -ENOMEM;
521 
522         memset(sma, 0, size);
523 
524         sma->sem_perm.mode = (semflg & S_IRWXUGO);
525         sma->sem_perm.key = key;
526 
527         sma->sem_perm.security = NULL;
528         retval = security_sem_alloc(sma);
529         if (retval) {
530                 ipc_rcu_putref(sma, ipc_rcu_free);
531                 return retval;
532         }
533 
534         sma->sem_base = (struct sem *) &sma[1];
535 
536         for (i = 0; i < nsems; i++) {
537                 INIT_LIST_HEAD(&sma->sem_base[i].pending_alter);
538                 INIT_LIST_HEAD(&sma->sem_base[i].pending_const);
539                 spin_lock_init(&sma->sem_base[i].lock);
540         }
541 
542         sma->complex_count = 0;
543         INIT_LIST_HEAD(&sma->pending_alter);
544         INIT_LIST_HEAD(&sma->pending_const);
545         INIT_LIST_HEAD(&sma->list_id);
546         sma->sem_nsems = nsems;
547         sma->sem_ctime = get_seconds();
548 
549         id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni);
550         if (id < 0) {
551                 ipc_rcu_putref(sma, sem_rcu_free);
552                 return id;
553         }
554         ns->used_sems += nsems;
555 
556         sem_unlock(sma, -1);
557         rcu_read_unlock();
558 
559         return sma->sem_perm.id;
560 }
561 
562 
563 /*
564  * Called with sem_ids.rwsem and ipcp locked.
565  */
566 static inline int sem_security(struct kern_ipc_perm *ipcp, int semflg)
567 {
568         struct sem_array *sma;
569 
570         sma = container_of(ipcp, struct sem_array, sem_perm);
571         return security_sem_associate(sma, semflg);
572 }
573 
574 /*
575  * Called with sem_ids.rwsem and ipcp locked.
576  */
577 static inline int sem_more_checks(struct kern_ipc_perm *ipcp,
578                                 struct ipc_params *params)
579 {
580         struct sem_array *sma;
581 
582         sma = container_of(ipcp, struct sem_array, sem_perm);
583         if (params->u.nsems > sma->sem_nsems)
584                 return -EINVAL;
585 
586         return 0;
587 }
588 
589 SYSCALL_DEFINE3(semget, key_t, key, int, nsems, int, semflg)
590 {
591         struct ipc_namespace *ns;
592         static const struct ipc_ops sem_ops = {
593                 .getnew = newary,
594                 .associate = sem_security,
595                 .more_checks = sem_more_checks,
596         };
597         struct ipc_params sem_params;
598 
599         ns = current->nsproxy->ipc_ns;
600 
601         if (nsems < 0 || nsems > ns->sc_semmsl)
602                 return -EINVAL;
603 
604         sem_params.key = key;
605         sem_params.flg = semflg;
606         sem_params.u.nsems = nsems;
607 
608         return ipcget(ns, &sem_ids(ns), &sem_ops, &sem_params);
609 }
610 
611 /**
612  * perform_atomic_semop - Perform (if possible) a semaphore operation
613  * @sma: semaphore array
614  * @q: struct sem_queue that describes the operation
615  *
616  * Returns 0 if the operation was possible.
617  * Returns 1 if the operation is impossible, the caller must sleep.
618  * Negative values are error codes.
619  */
620 static int perform_atomic_semop(struct sem_array *sma, struct sem_queue *q)
621 {
622         int result, sem_op, nsops, pid;
623         struct sembuf *sop;
624         struct sem *curr;
625         struct sembuf *sops;
626         struct sem_undo *un;
627 
628         sops = q->sops;
629         nsops = q->nsops;
630         un = q->undo;
631 
632         for (sop = sops; sop < sops + nsops; sop++) {
633                 curr = sma->sem_base + sop->sem_num;
634                 sem_op = sop->sem_op;
635                 result = curr->semval;
636 
637                 if (!sem_op && result)
638                         goto would_block;
639 
640                 result += sem_op;
641                 if (result < 0)
642                         goto would_block;
643                 if (result > SEMVMX)
644                         goto out_of_range;
645 
646                 if (sop->sem_flg & SEM_UNDO) {
647                         int undo = un->semadj[sop->sem_num] - sem_op;
648                         /* Exceeding the undo range is an error. */
649                         if (undo < (-SEMAEM - 1) || undo > SEMAEM)
650                                 goto out_of_range;
651                         un->semadj[sop->sem_num] = undo;
652                 }
653 
654                 curr->semval = result;
655         }
656 
657         sop--;
658         pid = q->pid;
659         while (sop >= sops) {
660                 sma->sem_base[sop->sem_num].sempid = pid;
661                 sop--;
662         }
663 
664         return 0;
665 
666 out_of_range:
667         result = -ERANGE;
668         goto undo;
669 
670 would_block:
671         q->blocking = sop;
672 
673         if (sop->sem_flg & IPC_NOWAIT)
674                 result = -EAGAIN;
675         else
676                 result = 1;
677 
678 undo:
679         sop--;
680         while (sop >= sops) {
681                 sem_op = sop->sem_op;
682                 sma->sem_base[sop->sem_num].semval -= sem_op;
683                 if (sop->sem_flg & SEM_UNDO)
684                         un->semadj[sop->sem_num] += sem_op;
685                 sop--;
686         }
687 
688         return result;
689 }
690 
691 /** wake_up_sem_queue_prepare(q, error): Prepare wake-up
692  * @q: queue entry that must be signaled
693  * @error: Error value for the signal
694  *
695  * Prepare the wake-up of the queue entry q.
696  */
697 static void wake_up_sem_queue_prepare(struct list_head *pt,
698                                 struct sem_queue *q, int error)
699 {
700         if (list_empty(pt)) {
701                 /*
702                  * Hold preempt off so that we don't get preempted and have the
703                  * wakee busy-wait until we're scheduled back on.
704                  */
705                 preempt_disable();
706         }
707         q->status = IN_WAKEUP;
708         q->pid = error;
709 
710         list_add_tail(&q->list, pt);
711 }
712 
713 /**
714  * wake_up_sem_queue_do - do the actual wake-up
715  * @pt: list of tasks to be woken up
716  *
717  * Do the actual wake-up.
718  * The function is called without any locks held, thus the semaphore array
719  * could be destroyed already and the tasks can disappear as soon as the
720  * status is set to the actual return code.
721  */
722 static void wake_up_sem_queue_do(struct list_head *pt)
723 {
724         struct sem_queue *q, *t;
725         int did_something;
726 
727         did_something = !list_empty(pt);
728         list_for_each_entry_safe(q, t, pt, list) {
729                 wake_up_process(q->sleeper);
730                 /* q can disappear immediately after writing q->status. */
731                 smp_wmb();
732                 q->status = q->pid;
733         }
734         if (did_something)
735                 preempt_enable();
736 }
737 
738 static void unlink_queue(struct sem_array *sma, struct sem_queue *q)
739 {
740         list_del(&q->list);
741         if (q->nsops > 1)
742                 sma->complex_count--;
743 }
744 
745 /** check_restart(sma, q)
746  * @sma: semaphore array
747  * @q: the operation that just completed
748  *
749  * update_queue is O(N^2) when it restarts scanning the whole queue of
750  * waiting operations. Therefore this function checks if the restart is
751  * really necessary. It is called after a previously waiting operation
752  * modified the array.
753  * Note that wait-for-zero operations are handled without restart.
754  */
755 static int check_restart(struct sem_array *sma, struct sem_queue *q)
756 {
757         /* pending complex alter operations are too difficult to analyse */
758         if (!list_empty(&sma->pending_alter))
759                 return 1;
760 
761         /* we were a sleeping complex operation. Too difficult */
762         if (q->nsops > 1)
763                 return 1;
764 
765         /* It is impossible that someone waits for the new value:
766          * - complex operations always restart.
767          * - wait-for-zero are handled seperately.
768          * - q is a previously sleeping simple operation that
769          *   altered the array. It must be a decrement, because
770          *   simple increments never sleep.
771          * - If there are older (higher priority) decrements
772          *   in the queue, then they have observed the original
773          *   semval value and couldn't proceed. The operation
774          *   decremented to value - thus they won't proceed either.
775          */
776         return 0;
777 }
778 
779 /**
780  * wake_const_ops - wake up non-alter tasks
781  * @sma: semaphore array.
782  * @semnum: semaphore that was modified.
783  * @pt: list head for the tasks that must be woken up.
784  *
785  * wake_const_ops must be called after a semaphore in a semaphore array
786  * was set to 0. If complex const operations are pending, wake_const_ops must
787  * be called with semnum = -1, as well as with the number of each modified
788  * semaphore.
789  * The tasks that must be woken up are added to @pt. The return code
790  * is stored in q->pid.
791  * The function returns 1 if at least one operation was completed successfully.
792  */
793 static int wake_const_ops(struct sem_array *sma, int semnum,
794                                 struct list_head *pt)
795 {
796         struct sem_queue *q;
797         struct list_head *walk;
798         struct list_head *pending_list;
799         int semop_completed = 0;
800 
801         if (semnum == -1)
802                 pending_list = &sma->pending_const;
803         else
804                 pending_list = &sma->sem_base[semnum].pending_const;
805 
806         walk = pending_list->next;
807         while (walk != pending_list) {
808                 int error;
809 
810                 q = container_of(walk, struct sem_queue, list);
811                 walk = walk->next;
812 
813                 error = perform_atomic_semop(sma, q);
814 
815                 if (error <= 0) {
816                         /* operation completed, remove from queue & wakeup */
817 
818                         unlink_queue(sma, q);
819 
820                         wake_up_sem_queue_prepare(pt, q, error);
821                         if (error == 0)
822                                 semop_completed = 1;
823                 }
824         }
825         return semop_completed;
826 }
827 
828 /**
829  * do_smart_wakeup_zero - wakeup all wait for zero tasks
830  * @sma: semaphore array
831  * @sops: operations that were performed
832  * @nsops: number of operations
833  * @pt: list head of the tasks that must be woken up.
834  *
835  * Checks all required queue for wait-for-zero operations, based
836  * on the actual changes that were performed on the semaphore array.
837  * The function returns 1 if at least one operation was completed successfully.
838  */
839 static int do_smart_wakeup_zero(struct sem_array *sma, struct sembuf *sops,
840                                         int nsops, struct list_head *pt)
841 {
842         int i;
843         int semop_completed = 0;
844         int got_zero = 0;
845 
846         /* first: the per-semaphore queues, if known */
847         if (sops) {
848                 for (i = 0; i < nsops; i++) {
849                         int num = sops[i].sem_num;
850 
851                         if (sma->sem_base[num].semval == 0) {
852                                 got_zero = 1;
853                                 semop_completed |= wake_const_ops(sma, num, pt);
854                         }
855                 }
856         } else {
857                 /*
858                  * No sops means modified semaphores not known.
859                  * Assume all were changed.
860                  */
861                 for (i = 0; i < sma->sem_nsems; i++) {
862                         if (sma->sem_base[i].semval == 0) {
863                                 got_zero = 1;
864                                 semop_completed |= wake_const_ops(sma, i, pt);
865                         }
866                 }
867         }
868         /*
869          * If one of the modified semaphores got 0,
870          * then check the global queue, too.
871          */
872         if (got_zero)
873                 semop_completed |= wake_const_ops(sma, -1, pt);
874 
875         return semop_completed;
876 }
877 
878 
879 /**
880  * update_queue - look for tasks that can be completed.
881  * @sma: semaphore array.
882  * @semnum: semaphore that was modified.
883  * @pt: list head for the tasks that must be woken up.
884  *
885  * update_queue must be called after a semaphore in a semaphore array
886  * was modified. If multiple semaphores were modified, update_queue must
887  * be called with semnum = -1, as well as with the number of each modified
888  * semaphore.
889  * The tasks that must be woken up are added to @pt. The return code
890  * is stored in q->pid.
891  * The function internally checks if const operations can now succeed.
892  *
893  * The function return 1 if at least one semop was completed successfully.
894  */
895 static int update_queue(struct sem_array *sma, int semnum, struct list_head *pt)
896 {
897         struct sem_queue *q;
898         struct list_head *walk;
899         struct list_head *pending_list;
900         int semop_completed = 0;
901 
902         if (semnum == -1)
903                 pending_list = &sma->pending_alter;
904         else
905                 pending_list = &sma->sem_base[semnum].pending_alter;
906 
907 again:
908         walk = pending_list->next;
909         while (walk != pending_list) {
910                 int error, restart;
911 
912                 q = container_of(walk, struct sem_queue, list);
913                 walk = walk->next;
914 
915                 /* If we are scanning the single sop, per-semaphore list of
916                  * one semaphore and that semaphore is 0, then it is not
917                  * necessary to scan further: simple increments
918                  * that affect only one entry succeed immediately and cannot
919                  * be in the  per semaphore pending queue, and decrements
920                  * cannot be successful if the value is already 0.
921                  */
922                 if (semnum != -1 && sma->sem_base[semnum].semval == 0)
923                         break;
924 
925                 error = perform_atomic_semop(sma, q);
926 
927                 /* Does q->sleeper still need to sleep? */
928                 if (error > 0)
929                         continue;
930 
931                 unlink_queue(sma, q);
932 
933                 if (error) {
934                         restart = 0;
935                 } else {
936                         semop_completed = 1;
937                         do_smart_wakeup_zero(sma, q->sops, q->nsops, pt);
938                         restart = check_restart(sma, q);
939                 }
940 
941                 wake_up_sem_queue_prepare(pt, q, error);
942                 if (restart)
943                         goto again;
944         }
945         return semop_completed;
946 }
947 
948 /**
949  * set_semotime - set sem_otime
950  * @sma: semaphore array
951  * @sops: operations that modified the array, may be NULL
952  *
953  * sem_otime is replicated to avoid cache line trashing.
954  * This function sets one instance to the current time.
955  */
956 static void set_semotime(struct sem_array *sma, struct sembuf *sops)
957 {
958         if (sops == NULL) {
959                 sma->sem_base[0].sem_otime = get_seconds();
960         } else {
961                 sma->sem_base[sops[0].sem_num].sem_otime =
962                                                         get_seconds();
963         }
964 }
965 
966 /**
967  * do_smart_update - optimized update_queue
968  * @sma: semaphore array
969  * @sops: operations that were performed
970  * @nsops: number of operations
971  * @otime: force setting otime
972  * @pt: list head of the tasks that must be woken up.
973  *
974  * do_smart_update() does the required calls to update_queue and wakeup_zero,
975  * based on the actual changes that were performed on the semaphore array.
976  * Note that the function does not do the actual wake-up: the caller is
977  * responsible for calling wake_up_sem_queue_do(@pt).
978  * It is safe to perform this call after dropping all locks.
979  */
980 static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsops,
981                         int otime, struct list_head *pt)
982 {
983         int i;
984 
985         otime |= do_smart_wakeup_zero(sma, sops, nsops, pt);
986 
987         if (!list_empty(&sma->pending_alter)) {
988                 /* semaphore array uses the global queue - just process it. */
989                 otime |= update_queue(sma, -1, pt);
990         } else {
991                 if (!sops) {
992                         /*
993                          * No sops, thus the modified semaphores are not
994                          * known. Check all.
995                          */
996                         for (i = 0; i < sma->sem_nsems; i++)
997                                 otime |= update_queue(sma, i, pt);
998                 } else {
999                         /*
1000                          * Check the semaphores that were increased:
1001                          * - No complex ops, thus all sleeping ops are
1002                          *   decrease.
1003                          * - if we decreased the value, then any sleeping
1004                          *   semaphore ops wont be able to run: If the
1005                          *   previous value was too small, then the new
1006                          *   value will be too small, too.
1007                          */
1008                         for (i = 0; i < nsops; i++) {
1009                                 if (sops[i].sem_op > 0) {
1010                                         otime |= update_queue(sma,
1011                                                         sops[i].sem_num, pt);
1012                                 }
1013                         }
1014                 }
1015         }
1016         if (otime)
1017                 set_semotime(sma, sops);
1018 }
1019 
1020 /*
1021  * check_qop: Test if a queued operation sleeps on the semaphore semnum
1022  */
1023 static int check_qop(struct sem_array *sma, int semnum, struct sem_queue *q,
1024                         bool count_zero)
1025 {
1026         struct sembuf *sop = q->blocking;
1027 
1028         /*
1029          * Linux always (since 0.99.10) reported a task as sleeping on all
1030          * semaphores. This violates SUS, therefore it was changed to the
1031          * standard compliant behavior.
1032          * Give the administrators a chance to notice that an application
1033          * might misbehave because it relies on the Linux behavior.
1034          */
1035         pr_info_once("semctl(GETNCNT/GETZCNT) is since 3.16 Single Unix Specification compliant.\n"
1036                         "The task %s (%d) triggered the difference, watch for misbehavior.\n",
1037                         current->comm, task_pid_nr(current));
1038 
1039         if (sop->sem_num != semnum)
1040                 return 0;
1041 
1042         if (count_zero && sop->sem_op == 0)
1043                 return 1;
1044         if (!count_zero && sop->sem_op < 0)
1045                 return 1;
1046 
1047         return 0;
1048 }
1049 
1050 /* The following counts are associated to each semaphore:
1051  *   semncnt        number of tasks waiting on semval being nonzero
1052  *   semzcnt        number of tasks waiting on semval being zero
1053  *
1054  * Per definition, a task waits only on the semaphore of the first semop
1055  * that cannot proceed, even if additional operation would block, too.
1056  */
1057 static int count_semcnt(struct sem_array *sma, ushort semnum,
1058                         bool count_zero)
1059 {
1060         struct list_head *l;
1061         struct sem_queue *q;
1062         int semcnt;
1063 
1064         semcnt = 0;
1065         /* First: check the simple operations. They are easy to evaluate */
1066         if (count_zero)
1067                 l = &sma->sem_base[semnum].pending_const;
1068         else
1069                 l = &sma->sem_base[semnum].pending_alter;
1070 
1071         list_for_each_entry(q, l, list) {
1072                 /* all task on a per-semaphore list sleep on exactly
1073                  * that semaphore
1074                  */
1075                 semcnt++;
1076         }
1077 
1078         /* Then: check the complex operations. */
1079         list_for_each_entry(q, &sma->pending_alter, list) {
1080                 semcnt += check_qop(sma, semnum, q, count_zero);
1081         }
1082         if (count_zero) {
1083                 list_for_each_entry(q, &sma->pending_const, list) {
1084                         semcnt += check_qop(sma, semnum, q, count_zero);
1085                 }
1086         }
1087         return semcnt;
1088 }
1089 
1090 /* Free a semaphore set. freeary() is called with sem_ids.rwsem locked
1091  * as a writer and the spinlock for this semaphore set hold. sem_ids.rwsem
1092  * remains locked on exit.
1093  */
1094 static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
1095 {
1096         struct sem_undo *un, *tu;
1097         struct sem_queue *q, *tq;
1098         struct sem_array *sma = container_of(ipcp, struct sem_array, sem_perm);
1099         struct list_head tasks;
1100         int i;
1101 
1102         /* Free the existing undo structures for this semaphore set.  */
1103         ipc_assert_locked_object(&sma->sem_perm);
1104         list_for_each_entry_safe(un, tu, &sma->list_id, list_id) {
1105                 list_del(&un->list_id);
1106                 spin_lock(&un->ulp->lock);
1107                 un->semid = -1;
1108                 list_del_rcu(&un->list_proc);
1109                 spin_unlock(&un->ulp->lock);
1110                 kfree_rcu(un, rcu);
1111         }
1112 
1113         /* Wake up all pending processes and let them fail with EIDRM. */
1114         INIT_LIST_HEAD(&tasks);
1115         list_for_each_entry_safe(q, tq, &sma->pending_const, list) {
1116                 unlink_queue(sma, q);
1117                 wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
1118         }
1119 
1120         list_for_each_entry_safe(q, tq, &sma->pending_alter, list) {
1121                 unlink_queue(sma, q);
1122                 wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
1123         }
1124         for (i = 0; i < sma->sem_nsems; i++) {
1125                 struct sem *sem = sma->sem_base + i;
1126                 list_for_each_entry_safe(q, tq, &sem->pending_const, list) {
1127                         unlink_queue(sma, q);
1128                         wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
1129                 }
1130                 list_for_each_entry_safe(q, tq, &sem->pending_alter, list) {
1131                         unlink_queue(sma, q);
1132                         wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
1133                 }
1134         }
1135 
1136         /* Remove the semaphore set from the IDR */
1137         sem_rmid(ns, sma);
1138         sem_unlock(sma, -1);
1139         rcu_read_unlock();
1140 
1141         wake_up_sem_queue_do(&tasks);
1142         ns->used_sems -= sma->sem_nsems;
1143         ipc_rcu_putref(sma, sem_rcu_free);
1144 }
1145 
1146 static unsigned long copy_semid_to_user(void __user *buf, struct semid64_ds *in, int version)
1147 {
1148         switch (version) {
1149         case IPC_64:
1150                 return copy_to_user(buf, in, sizeof(*in));
1151         case IPC_OLD:
1152             {
1153                 struct semid_ds out;
1154 
1155                 memset(&out, 0, sizeof(out));
1156 
1157                 ipc64_perm_to_ipc_perm(&in->sem_perm, &out.sem_perm);
1158 
1159                 out.sem_otime   = in->sem_otime;
1160                 out.sem_ctime   = in->sem_ctime;
1161                 out.sem_nsems   = in->sem_nsems;
1162 
1163                 return copy_to_user(buf, &out, sizeof(out));
1164             }
1165         default:
1166                 return -EINVAL;
1167         }
1168 }
1169 
1170 static time_t get_semotime(struct sem_array *sma)
1171 {
1172         int i;
1173         time_t res;
1174 
1175         res = sma->sem_base[0].sem_otime;
1176         for (i = 1; i < sma->sem_nsems; i++) {
1177                 time_t to = sma->sem_base[i].sem_otime;
1178 
1179                 if (to > res)
1180                         res = to;
1181         }
1182         return res;
1183 }
1184 
1185 static int semctl_nolock(struct ipc_namespace *ns, int semid,
1186                          int cmd, int version, void __user *p)
1187 {
1188         int err;
1189         struct sem_array *sma;
1190 
1191         switch (cmd) {
1192         case IPC_INFO:
1193         case SEM_INFO:
1194         {
1195                 struct seminfo seminfo;
1196                 int max_id;
1197 
1198                 err = security_sem_semctl(NULL, cmd);
1199                 if (err)
1200                         return err;
1201 
1202                 memset(&seminfo, 0, sizeof(seminfo));
1203                 seminfo.semmni = ns->sc_semmni;
1204                 seminfo.semmns = ns->sc_semmns;
1205                 seminfo.semmsl = ns->sc_semmsl;
1206                 seminfo.semopm = ns->sc_semopm;
1207                 seminfo.semvmx = SEMVMX;
1208                 seminfo.semmnu = SEMMNU;
1209                 seminfo.semmap = SEMMAP;
1210                 seminfo.semume = SEMUME;
1211                 down_read(&sem_ids(ns).rwsem);
1212                 if (cmd == SEM_INFO) {
1213                         seminfo.semusz = sem_ids(ns).in_use;
1214                         seminfo.semaem = ns->used_sems;
1215                 } else {
1216                         seminfo.semusz = SEMUSZ;
1217                         seminfo.semaem = SEMAEM;
1218                 }
1219                 max_id = ipc_get_maxid(&sem_ids(ns));
1220                 up_read(&sem_ids(ns).rwsem);
1221                 if (copy_to_user(p, &seminfo, sizeof(struct seminfo)))
1222                         return -EFAULT;
1223                 return (max_id < 0) ? 0 : max_id;
1224         }
1225         case IPC_STAT:
1226         case SEM_STAT:
1227         {
1228                 struct semid64_ds tbuf;
1229                 int id = 0;
1230 
1231                 memset(&tbuf, 0, sizeof(tbuf));
1232 
1233                 rcu_read_lock();
1234                 if (cmd == SEM_STAT) {
1235                         sma = sem_obtain_object(ns, semid);
1236                         if (IS_ERR(sma)) {
1237                                 err = PTR_ERR(sma);
1238                                 goto out_unlock;
1239                         }
1240                         id = sma->sem_perm.id;
1241                 } else {
1242                         sma = sem_obtain_object_check(ns, semid);
1243                         if (IS_ERR(sma)) {
1244                                 err = PTR_ERR(sma);
1245                                 goto out_unlock;
1246                         }
1247                 }
1248 
1249                 err = -EACCES;
1250                 if (ipcperms(ns, &sma->sem_perm, S_IRUGO))
1251                         goto out_unlock;
1252 
1253                 err = security_sem_semctl(sma, cmd);
1254                 if (err)
1255                         goto out_unlock;
1256 
1257                 kernel_to_ipc64_perm(&sma->sem_perm, &tbuf.sem_perm);
1258                 tbuf.sem_otime = get_semotime(sma);
1259                 tbuf.sem_ctime = sma->sem_ctime;
1260                 tbuf.sem_nsems = sma->sem_nsems;
1261                 rcu_read_unlock();
1262                 if (copy_semid_to_user(p, &tbuf, version))
1263                         return -EFAULT;
1264                 return id;
1265         }
1266         default:
1267                 return -EINVAL;
1268         }
1269 out_unlock:
1270         rcu_read_unlock();
1271         return err;
1272 }
1273 
1274 static int semctl_setval(struct ipc_namespace *ns, int semid, int semnum,
1275                 unsigned long arg)
1276 {
1277         struct sem_undo *un;
1278         struct sem_array *sma;
1279         struct sem *curr;
1280         int err;
1281         struct list_head tasks;
1282         int val;
1283 #if defined(CONFIG_64BIT) && defined(__BIG_ENDIAN)
1284         /* big-endian 64bit */
1285         val = arg >> 32;
1286 #else
1287         /* 32bit or little-endian 64bit */
1288         val = arg;
1289 #endif
1290 
1291         if (val > SEMVMX || val < 0)
1292                 return -ERANGE;
1293 
1294         INIT_LIST_HEAD(&tasks);
1295 
1296         rcu_read_lock();
1297         sma = sem_obtain_object_check(ns, semid);
1298         if (IS_ERR(sma)) {
1299                 rcu_read_unlock();
1300                 return PTR_ERR(sma);
1301         }
1302 
1303         if (semnum < 0 || semnum >= sma->sem_nsems) {
1304                 rcu_read_unlock();
1305                 return -EINVAL;
1306         }
1307 
1308 
1309         if (ipcperms(ns, &sma->sem_perm, S_IWUGO)) {
1310                 rcu_read_unlock();
1311                 return -EACCES;
1312         }
1313 
1314         err = security_sem_semctl(sma, SETVAL);
1315         if (err) {
1316                 rcu_read_unlock();
1317                 return -EACCES;
1318         }
1319 
1320         sem_lock(sma, NULL, -1);
1321 
1322         if (!ipc_valid_object(&sma->sem_perm)) {
1323                 sem_unlock(sma, -1);
1324                 rcu_read_unlock();
1325                 return -EIDRM;
1326         }
1327 
1328         curr = &sma->sem_base[semnum];
1329 
1330         ipc_assert_locked_object(&sma->sem_perm);
1331         list_for_each_entry(un, &sma->list_id, list_id)
1332                 un->semadj[semnum] = 0;
1333 
1334         curr->semval = val;
1335         curr->sempid = task_tgid_vnr(current);
1336         sma->sem_ctime = get_seconds();
1337         /* maybe some queued-up processes were waiting for this */
1338         do_smart_update(sma, NULL, 0, 0, &tasks);
1339         sem_unlock(sma, -1);
1340         rcu_read_unlock();
1341         wake_up_sem_queue_do(&tasks);
1342         return 0;
1343 }
1344 
1345 static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
1346                 int cmd, void __user *p)
1347 {
1348         struct sem_array *sma;
1349         struct sem *curr;
1350         int err, nsems;
1351         ushort fast_sem_io[SEMMSL_FAST];
1352         ushort *sem_io = fast_sem_io;
1353         struct list_head tasks;
1354 
1355         INIT_LIST_HEAD(&tasks);
1356 
1357         rcu_read_lock();
1358         sma = sem_obtain_object_check(ns, semid);
1359         if (IS_ERR(sma)) {
1360                 rcu_read_unlock();
1361                 return PTR_ERR(sma);
1362         }
1363 
1364         nsems = sma->sem_nsems;
1365 
1366         err = -EACCES;
1367         if (ipcperms(ns, &sma->sem_perm, cmd == SETALL ? S_IWUGO : S_IRUGO))
1368                 goto out_rcu_wakeup;
1369 
1370         err = security_sem_semctl(sma, cmd);
1371         if (err)
1372                 goto out_rcu_wakeup;
1373 
1374         err = -EACCES;
1375         switch (cmd) {
1376         case GETALL:
1377         {
1378                 ushort __user *array = p;
1379                 int i;
1380 
1381                 sem_lock(sma, NULL, -1);
1382                 if (!ipc_valid_object(&sma->sem_perm)) {
1383                         err = -EIDRM;
1384                         goto out_unlock;
1385                 }
1386                 if (nsems > SEMMSL_FAST) {
1387                         if (!ipc_rcu_getref(sma)) {
1388                                 err = -EIDRM;
1389                                 goto out_unlock;
1390                         }
1391                         sem_unlock(sma, -1);
1392                         rcu_read_unlock();
1393                         sem_io = ipc_alloc(sizeof(ushort)*nsems);
1394                         if (sem_io == NULL) {
1395                                 ipc_rcu_putref(sma, ipc_rcu_free);
1396                                 return -ENOMEM;
1397                         }
1398 
1399                         rcu_read_lock();
1400                         sem_lock_and_putref(sma);
1401                         if (!ipc_valid_object(&sma->sem_perm)) {
1402                                 err = -EIDRM;
1403                                 goto out_unlock;
1404                         }
1405                 }
1406                 for (i = 0; i < sma->sem_nsems; i++)
1407                         sem_io[i] = sma->sem_base[i].semval;
1408                 sem_unlock(sma, -1);
1409                 rcu_read_unlock();
1410                 err = 0;
1411                 if (copy_to_user(array, sem_io, nsems*sizeof(ushort)))
1412                         err = -EFAULT;
1413                 goto out_free;
1414         }
1415         case SETALL:
1416         {
1417                 int i;
1418                 struct sem_undo *un;
1419 
1420                 if (!ipc_rcu_getref(sma)) {
1421                         err = -EIDRM;
1422                         goto out_rcu_wakeup;
1423                 }
1424                 rcu_read_unlock();
1425 
1426                 if (nsems > SEMMSL_FAST) {
1427                         sem_io = ipc_alloc(sizeof(ushort)*nsems);
1428                         if (sem_io == NULL) {
1429                                 ipc_rcu_putref(sma, ipc_rcu_free);
1430                                 return -ENOMEM;
1431                         }
1432                 }
1433 
1434                 if (copy_from_user(sem_io, p, nsems*sizeof(ushort))) {
1435                         ipc_rcu_putref(sma, ipc_rcu_free);
1436                         err = -EFAULT;
1437                         goto out_free;
1438                 }
1439 
1440                 for (i = 0; i < nsems; i++) {
1441                         if (sem_io[i] > SEMVMX) {
1442                                 ipc_rcu_putref(sma, ipc_rcu_free);
1443                                 err = -ERANGE;
1444                                 goto out_free;
1445                         }
1446                 }
1447                 rcu_read_lock();
1448                 sem_lock_and_putref(sma);
1449                 if (!ipc_valid_object(&sma->sem_perm)) {
1450                         err = -EIDRM;
1451                         goto out_unlock;
1452                 }
1453 
1454                 for (i = 0; i < nsems; i++) {
1455                         sma->sem_base[i].semval = sem_io[i];
1456                         sma->sem_base[i].sempid = task_tgid_vnr(current);
1457                 }
1458 
1459                 ipc_assert_locked_object(&sma->sem_perm);
1460                 list_for_each_entry(un, &sma->list_id, list_id) {
1461                         for (i = 0; i < nsems; i++)
1462                                 un->semadj[i] = 0;
1463                 }
1464                 sma->sem_ctime = get_seconds();
1465                 /* maybe some queued-up processes were waiting for this */
1466                 do_smart_update(sma, NULL, 0, 0, &tasks);
1467                 err = 0;
1468                 goto out_unlock;
1469         }
1470         /* GETVAL, GETPID, GETNCTN, GETZCNT: fall-through */
1471         }
1472         err = -EINVAL;
1473         if (semnum < 0 || semnum >= nsems)
1474                 goto out_rcu_wakeup;
1475 
1476         sem_lock(sma, NULL, -1);
1477         if (!ipc_valid_object(&sma->sem_perm)) {
1478                 err = -EIDRM;
1479                 goto out_unlock;
1480         }
1481         curr = &sma->sem_base[semnum];
1482 
1483         switch (cmd) {
1484         case GETVAL:
1485                 err = curr->semval;
1486                 goto out_unlock;
1487         case GETPID:
1488                 err = curr->sempid;
1489                 goto out_unlock;
1490         case GETNCNT:
1491                 err = count_semcnt(sma, semnum, 0);
1492                 goto out_unlock;
1493         case GETZCNT:
1494                 err = count_semcnt(sma, semnum, 1);
1495                 goto out_unlock;
1496         }
1497 
1498 out_unlock:
1499         sem_unlock(sma, -1);
1500 out_rcu_wakeup:
1501         rcu_read_unlock();
1502         wake_up_sem_queue_do(&tasks);
1503 out_free:
1504         if (sem_io != fast_sem_io)
1505                 ipc_free(sem_io);
1506         return err;
1507 }
1508 
1509 static inline unsigned long
1510 copy_semid_from_user(struct semid64_ds *out, void __user *buf, int version)
1511 {
1512         switch (version) {
1513         case IPC_64:
1514                 if (copy_from_user(out, buf, sizeof(*out)))
1515                         return -EFAULT;
1516                 return 0;
1517         case IPC_OLD:
1518             {
1519                 struct semid_ds tbuf_old;
1520 
1521                 if (copy_from_user(&tbuf_old, buf, sizeof(tbuf_old)))
1522                         return -EFAULT;
1523 
1524                 out->sem_perm.uid       = tbuf_old.sem_perm.uid;
1525                 out->sem_perm.gid       = tbuf_old.sem_perm.gid;
1526                 out->sem_perm.mode      = tbuf_old.sem_perm.mode;
1527 
1528                 return 0;
1529             }
1530         default:
1531                 return -EINVAL;
1532         }
1533 }
1534 
1535 /*
1536  * This function handles some semctl commands which require the rwsem
1537  * to be held in write mode.
1538  * NOTE: no locks must be held, the rwsem is taken inside this function.
1539  */
1540 static int semctl_down(struct ipc_namespace *ns, int semid,
1541                        int cmd, int version, void __user *p)
1542 {
1543         struct sem_array *sma;
1544         int err;
1545         struct semid64_ds semid64;
1546         struct kern_ipc_perm *ipcp;
1547 
1548         if (cmd == IPC_SET) {
1549                 if (copy_semid_from_user(&semid64, p, version))
1550                         return -EFAULT;
1551         }
1552 
1553         down_write(&sem_ids(ns).rwsem);
1554         rcu_read_lock();
1555 
1556         ipcp = ipcctl_pre_down_nolock(ns, &sem_ids(ns), semid, cmd,
1557                                       &semid64.sem_perm, 0);
1558         if (IS_ERR(ipcp)) {
1559                 err = PTR_ERR(ipcp);
1560                 goto out_unlock1;
1561         }
1562 
1563         sma = container_of(ipcp, struct sem_array, sem_perm);
1564 
1565         err = security_sem_semctl(sma, cmd);
1566         if (err)
1567                 goto out_unlock1;
1568 
1569         switch (cmd) {
1570         case IPC_RMID:
1571                 sem_lock(sma, NULL, -1);
1572                 /* freeary unlocks the ipc object and rcu */
1573                 freeary(ns, ipcp);
1574                 goto out_up;
1575         case IPC_SET:
1576                 sem_lock(sma, NULL, -1);
1577                 err = ipc_update_perm(&semid64.sem_perm, ipcp);
1578                 if (err)
1579                         goto out_unlock0;
1580                 sma->sem_ctime = get_seconds();
1581                 break;
1582         default:
1583                 err = -EINVAL;
1584                 goto out_unlock1;
1585         }
1586 
1587 out_unlock0:
1588         sem_unlock(sma, -1);
1589 out_unlock1:
1590         rcu_read_unlock();
1591 out_up:
1592         up_write(&sem_ids(ns).rwsem);
1593         return err;
1594 }
1595 
1596 SYSCALL_DEFINE4(semctl, int, semid, int, semnum, int, cmd, unsigned long, arg)
1597 {
1598         int version;
1599         struct ipc_namespace *ns;
1600         void __user *p = (void __user *)arg;
1601 
1602         if (semid < 0)
1603                 return -EINVAL;
1604 
1605         version = ipc_parse_version(&cmd);
1606         ns = current->nsproxy->ipc_ns;
1607 
1608         switch (cmd) {
1609         case IPC_INFO:
1610         case SEM_INFO:
1611         case IPC_STAT:
1612         case SEM_STAT:
1613                 return semctl_nolock(ns, semid, cmd, version, p);
1614         case GETALL:
1615         case GETVAL:
1616         case GETPID:
1617         case GETNCNT:
1618         case GETZCNT:
1619         case SETALL:
1620                 return semctl_main(ns, semid, semnum, cmd, p);
1621         case SETVAL:
1622                 return semctl_setval(ns, semid, semnum, arg);
1623         case IPC_RMID:
1624         case IPC_SET:
1625                 return semctl_down(ns, semid, cmd, version, p);
1626         default:
1627                 return -EINVAL;
1628         }
1629 }
1630 
1631 /* If the task doesn't already have a undo_list, then allocate one
1632  * here.  We guarantee there is only one thread using this undo list,
1633  * and current is THE ONE
1634  *
1635  * If this allocation and assignment succeeds, but later
1636  * portions of this code fail, there is no need to free the sem_undo_list.
1637  * Just let it stay associated with the task, and it'll be freed later
1638  * at exit time.
1639  *
1640  * This can block, so callers must hold no locks.
1641  */
1642 static inline int get_undo_list(struct sem_undo_list **undo_listp)
1643 {
1644         struct sem_undo_list *undo_list;
1645 
1646         undo_list = current->sysvsem.undo_list;
1647         if (!undo_list) {
1648                 undo_list = kzalloc(sizeof(*undo_list), GFP_KERNEL);
1649                 if (undo_list == NULL)
1650                         return -ENOMEM;
1651                 spin_lock_init(&undo_list->lock);
1652                 atomic_set(&undo_list->refcnt, 1);
1653                 INIT_LIST_HEAD(&undo_list->list_proc);
1654 
1655                 current->sysvsem.undo_list = undo_list;
1656         }
1657         *undo_listp = undo_list;
1658         return 0;
1659 }
1660 
1661 static struct sem_undo *__lookup_undo(struct sem_undo_list *ulp, int semid)
1662 {
1663         struct sem_undo *un;
1664 
1665         list_for_each_entry_rcu(un, &ulp->list_proc, list_proc) {
1666                 if (un->semid == semid)
1667                         return un;
1668         }
1669         return NULL;
1670 }
1671 
1672 static struct sem_undo *lookup_undo(struct sem_undo_list *ulp, int semid)
1673 {
1674         struct sem_undo *un;
1675 
1676         assert_spin_locked(&ulp->lock);
1677 
1678         un = __lookup_undo(ulp, semid);
1679         if (un) {
1680                 list_del_rcu(&un->list_proc);
1681                 list_add_rcu(&un->list_proc, &ulp->list_proc);
1682         }
1683         return un;
1684 }
1685 
1686 /**
1687  * find_alloc_undo - lookup (and if not present create) undo array
1688  * @ns: namespace
1689  * @semid: semaphore array id
1690  *
1691  * The function looks up (and if not present creates) the undo structure.
1692  * The size of the undo structure depends on the size of the semaphore
1693  * array, thus the alloc path is not that straightforward.
1694  * Lifetime-rules: sem_undo is rcu-protected, on success, the function
1695  * performs a rcu_read_lock().
1696  */
1697 static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
1698 {
1699         struct sem_array *sma;
1700         struct sem_undo_list *ulp;
1701         struct sem_undo *un, *new;
1702         int nsems, error;
1703 
1704         error = get_undo_list(&ulp);
1705         if (error)
1706                 return ERR_PTR(error);
1707 
1708         rcu_read_lock();
1709         spin_lock(&ulp->lock);
1710         un = lookup_undo(ulp, semid);
1711         spin_unlock(&ulp->lock);
1712         if (likely(un != NULL))
1713                 goto out;
1714 
1715         /* no undo structure around - allocate one. */
1716         /* step 1: figure out the size of the semaphore array */
1717         sma = sem_obtain_object_check(ns, semid);
1718         if (IS_ERR(sma)) {
1719                 rcu_read_unlock();
1720                 return ERR_CAST(sma);
1721         }
1722 
1723         nsems = sma->sem_nsems;
1724         if (!ipc_rcu_getref(sma)) {
1725                 rcu_read_unlock();
1726                 un = ERR_PTR(-EIDRM);
1727                 goto out;
1728         }
1729         rcu_read_unlock();
1730 
1731         /* step 2: allocate new undo structure */
1732         new = kzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems, GFP_KERNEL);
1733         if (!new) {
1734                 ipc_rcu_putref(sma, ipc_rcu_free);
1735                 return ERR_PTR(-ENOMEM);
1736         }
1737 
1738         /* step 3: Acquire the lock on semaphore array */
1739         rcu_read_lock();
1740         sem_lock_and_putref(sma);
1741         if (!ipc_valid_object(&sma->sem_perm)) {
1742                 sem_unlock(sma, -1);
1743                 rcu_read_unlock();
1744                 kfree(new);
1745                 un = ERR_PTR(-EIDRM);
1746                 goto out;
1747         }
1748         spin_lock(&ulp->lock);
1749 
1750         /*
1751          * step 4: check for races: did someone else allocate the undo struct?
1752          */
1753         un = lookup_undo(ulp, semid);
1754         if (un) {
1755                 kfree(new);
1756                 goto success;
1757         }
1758         /* step 5: initialize & link new undo structure */
1759         new->semadj = (short *) &new[1];
1760         new->ulp = ulp;
1761         new->semid = semid;
1762         assert_spin_locked(&ulp->lock);
1763         list_add_rcu(&new->list_proc, &ulp->list_proc);
1764         ipc_assert_locked_object(&sma->sem_perm);
1765         list_add(&new->list_id, &sma->list_id);
1766         un = new;
1767 
1768 success:
1769         spin_unlock(&ulp->lock);
1770         sem_unlock(sma, -1);
1771 out:
1772         return un;
1773 }
1774 
1775 
1776 /**
1777  * get_queue_result - retrieve the result code from sem_queue
1778  * @q: Pointer to queue structure
1779  *
1780  * Retrieve the return code from the pending queue. If IN_WAKEUP is found in
1781  * q->status, then we must loop until the value is replaced with the final
1782  * value: This may happen if a task is woken up by an unrelated event (e.g.
1783  * signal) and in parallel the task is woken up by another task because it got
1784  * the requested semaphores.
1785  *
1786  * The function can be called with or without holding the semaphore spinlock.
1787  */
1788 static int get_queue_result(struct sem_queue *q)
1789 {
1790         int error;
1791 
1792         error = q->status;
1793         while (unlikely(error == IN_WAKEUP)) {
1794                 cpu_relax();
1795                 error = q->status;
1796         }
1797 
1798         return error;
1799 }
1800 
1801 SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
1802                 unsigned, nsops, const struct timespec __user *, timeout)
1803 {
1804         int error = -EINVAL;
1805         struct sem_array *sma;
1806         struct sembuf fast_sops[SEMOPM_FAST];
1807         struct sembuf *sops = fast_sops, *sop;
1808         struct sem_undo *un;
1809         int undos = 0, alter = 0, max, locknum;
1810         struct sem_queue queue;
1811         unsigned long jiffies_left = 0;
1812         struct ipc_namespace *ns;
1813         struct list_head tasks;
1814 
1815         ns = current->nsproxy->ipc_ns;
1816 
1817         if (nsops < 1 || semid < 0)
1818                 return -EINVAL;
1819         if (nsops > ns->sc_semopm)
1820                 return -E2BIG;
1821         if (nsops > SEMOPM_FAST) {
1822                 sops = kmalloc(sizeof(*sops)*nsops, GFP_KERNEL);
1823                 if (sops == NULL)
1824                         return -ENOMEM;
1825         }
1826         if (copy_from_user(sops, tsops, nsops * sizeof(*tsops))) {
1827                 error =  -EFAULT;
1828                 goto out_free;
1829         }
1830         if (timeout) {
1831                 struct timespec _timeout;
1832                 if (copy_from_user(&_timeout, timeout, sizeof(*timeout))) {
1833                         error = -EFAULT;
1834                         goto out_free;
1835                 }
1836                 if (_timeout.tv_sec < 0 || _timeout.tv_nsec < 0 ||
1837                         _timeout.tv_nsec >= 1000000000L) {
1838                         error = -EINVAL;
1839                         goto out_free;
1840                 }
1841                 jiffies_left = timespec_to_jiffies(&_timeout);
1842         }
1843         max = 0;
1844         for (sop = sops; sop < sops + nsops; sop++) {
1845                 if (sop->sem_num >= max)
1846                         max = sop->sem_num;
1847                 if (sop->sem_flg & SEM_UNDO)
1848                         undos = 1;
1849                 if (sop->sem_op != 0)
1850                         alter = 1;
1851         }
1852 
1853         INIT_LIST_HEAD(&tasks);
1854 
1855         if (undos) {
1856                 /* On success, find_alloc_undo takes the rcu_read_lock */
1857                 un = find_alloc_undo(ns, semid);
1858                 if (IS_ERR(un)) {
1859                         error = PTR_ERR(un);
1860                         goto out_free;
1861                 }
1862         } else {
1863                 un = NULL;
1864                 rcu_read_lock();
1865         }
1866 
1867         sma = sem_obtain_object_check(ns, semid);
1868         if (IS_ERR(sma)) {
1869                 rcu_read_unlock();
1870                 error = PTR_ERR(sma);
1871                 goto out_free;
1872         }
1873 
1874         error = -EFBIG;
1875         if (max >= sma->sem_nsems)
1876                 goto out_rcu_wakeup;
1877 
1878         error = -EACCES;
1879         if (ipcperms(ns, &sma->sem_perm, alter ? S_IWUGO : S_IRUGO))
1880                 goto out_rcu_wakeup;
1881 
1882         error = security_sem_semop(sma, sops, nsops, alter);
1883         if (error)
1884                 goto out_rcu_wakeup;
1885 
1886         error = -EIDRM;
1887         locknum = sem_lock(sma, sops, nsops);
1888         /*
1889          * We eventually might perform the following check in a lockless
1890          * fashion, considering ipc_valid_object() locking constraints.
1891          * If nsops == 1 and there is no contention for sem_perm.lock, then
1892          * only a per-semaphore lock is held and it's OK to proceed with the
1893          * check below. More details on the fine grained locking scheme
1894          * entangled here and why it's RMID race safe on comments at sem_lock()
1895          */
1896         if (!ipc_valid_object(&sma->sem_perm))
1897                 goto out_unlock_free;
1898         /*
1899          * semid identifiers are not unique - find_alloc_undo may have
1900          * allocated an undo structure, it was invalidated by an RMID
1901          * and now a new array with received the same id. Check and fail.
1902          * This case can be detected checking un->semid. The existence of
1903          * "un" itself is guaranteed by rcu.
1904          */
1905         if (un && un->semid == -1)
1906                 goto out_unlock_free;
1907 
1908         queue.sops = sops;
1909         queue.nsops = nsops;
1910         queue.undo = un;
1911         queue.pid = task_tgid_vnr(current);
1912         queue.alter = alter;
1913 
1914         error = perform_atomic_semop(sma, &queue);
1915         if (error == 0) {
1916                 /* If the operation was successful, then do
1917                  * the required updates.
1918                  */
1919                 if (alter)
1920                         do_smart_update(sma, sops, nsops, 1, &tasks);
1921                 else
1922                         set_semotime(sma, sops);
1923         }
1924         if (error <= 0)
1925                 goto out_unlock_free;
1926 
1927         /* We need to sleep on this operation, so we put the current
1928          * task into the pending queue and go to sleep.
1929          */
1930 
1931         if (nsops == 1) {
1932                 struct sem *curr;
1933                 curr = &sma->sem_base[sops->sem_num];
1934 
1935                 if (alter) {
1936                         if (sma->complex_count) {
1937                                 list_add_tail(&queue.list,
1938                                                 &sma->pending_alter);
1939                         } else {
1940 
1941                                 list_add_tail(&queue.list,
1942                                                 &curr->pending_alter);
1943                         }
1944                 } else {
1945                         list_add_tail(&queue.list, &curr->pending_const);
1946                 }
1947         } else {
1948                 if (!sma->complex_count)
1949                         merge_queues(sma);
1950 
1951                 if (alter)
1952                         list_add_tail(&queue.list, &sma->pending_alter);
1953                 else
1954                         list_add_tail(&queue.list, &sma->pending_const);
1955 
1956                 sma->complex_count++;
1957         }
1958 
1959         queue.status = -EINTR;
1960         queue.sleeper = current;
1961 
1962 sleep_again:
1963         __set_current_state(TASK_INTERRUPTIBLE);
1964         sem_unlock(sma, locknum);
1965         rcu_read_unlock();
1966 
1967         if (timeout)
1968                 jiffies_left = schedule_timeout(jiffies_left);
1969         else
1970                 schedule();
1971 
1972         error = get_queue_result(&queue);
1973 
1974         if (error != -EINTR) {
1975                 /* fast path: update_queue already obtained all requested
1976                  * resources.
1977                  * Perform a smp_mb(): User space could assume that semop()
1978                  * is a memory barrier: Without the mb(), the cpu could
1979                  * speculatively read in user space stale data that was
1980                  * overwritten by the previous owner of the semaphore.
1981                  */
1982                 smp_mb();
1983 
1984                 goto out_free;
1985         }
1986 
1987         rcu_read_lock();
1988         sma = sem_obtain_lock(ns, semid, sops, nsops, &locknum);
1989 
1990         /*
1991          * Wait until it's guaranteed that no wakeup_sem_queue_do() is ongoing.
1992          */
1993         error = get_queue_result(&queue);
1994 
1995         /*
1996          * Array removed? If yes, leave without sem_unlock().
1997          */
1998         if (IS_ERR(sma)) {
1999                 rcu_read_unlock();
2000                 goto out_free;
2001         }
2002 
2003 
2004         /*
2005          * If queue.status != -EINTR we are woken up by another process.
2006          * Leave without unlink_queue(), but with sem_unlock().
2007          */
2008         if (error != -EINTR)
2009                 goto out_unlock_free;
2010 
2011         /*
2012          * If an interrupt occurred we have to clean up the queue
2013          */
2014         if (timeout && jiffies_left == 0)
2015                 error = -EAGAIN;
2016 
2017         /*
2018          * If the wakeup was spurious, just retry
2019          */
2020         if (error == -EINTR && !signal_pending(current))
2021                 goto sleep_again;
2022 
2023         unlink_queue(sma, &queue);
2024 
2025 out_unlock_free:
2026         sem_unlock(sma, locknum);
2027 out_rcu_wakeup:
2028         rcu_read_unlock();
2029         wake_up_sem_queue_do(&tasks);
2030 out_free:
2031         if (sops != fast_sops)
2032                 kfree(sops);
2033         return error;
2034 }
2035 
2036 SYSCALL_DEFINE3(semop, int, semid, struct sembuf __user *, tsops,
2037                 unsigned, nsops)
2038 {
2039         return sys_semtimedop(semid, tsops, nsops, NULL);
2040 }
2041 
2042 /* If CLONE_SYSVSEM is set, establish sharing of SEM_UNDO state between
2043  * parent and child tasks.
2044  */
2045 
2046 int copy_semundo(unsigned long clone_flags, struct task_struct *tsk)
2047 {
2048         struct sem_undo_list *undo_list;
2049         int error;
2050 
2051         if (clone_flags & CLONE_SYSVSEM) {
2052                 error = get_undo_list(&undo_list);
2053                 if (error)
2054                         return error;
2055                 atomic_inc(&undo_list->refcnt);
2056                 tsk->sysvsem.undo_list = undo_list;
2057         } else
2058                 tsk->sysvsem.undo_list = NULL;
2059 
2060         return 0;
2061 }
2062 
2063 /*
2064  * add semadj values to semaphores, free undo structures.
2065  * undo structures are not freed when semaphore arrays are destroyed
2066  * so some of them may be out of date.
2067  * IMPLEMENTATION NOTE: There is some confusion over whether the
2068  * set of adjustments that needs to be done should be done in an atomic
2069  * manner or not. That is, if we are attempting to decrement the semval
2070  * should we queue up and wait until we can do so legally?
2071  * The original implementation attempted to do this (queue and wait).
2072  * The current implementation does not do so. The POSIX standard
2073  * and SVID should be consulted to determine what behavior is mandated.
2074  */
2075 void exit_sem(struct task_struct *tsk)
2076 {
2077         struct sem_undo_list *ulp;
2078 
2079         ulp = tsk->sysvsem.undo_list;
2080         if (!ulp)
2081                 return;
2082         tsk->sysvsem.undo_list = NULL;
2083 
2084         if (!atomic_dec_and_test(&ulp->refcnt))
2085                 return;
2086 
2087         for (;;) {
2088                 struct sem_array *sma;
2089                 struct sem_undo *un;
2090                 struct list_head tasks;
2091                 int semid, i;
2092 
2093                 rcu_read_lock();
2094                 un = list_entry_rcu(ulp->list_proc.next,
2095                                     struct sem_undo, list_proc);
2096                 if (&un->list_proc == &ulp->list_proc) {
2097                         /*
2098                          * We must wait for freeary() before freeing this ulp,
2099                          * in case we raced with last sem_undo. There is a small
2100                          * possibility where we exit while freeary() didn't
2101                          * finish unlocking sem_undo_list.
2102                          */
2103                         spin_unlock_wait(&ulp->lock);
2104                         rcu_read_unlock();
2105                         break;
2106                 }
2107                 spin_lock(&ulp->lock);
2108                 semid = un->semid;
2109                 spin_unlock(&ulp->lock);
2110 
2111                 /* exit_sem raced with IPC_RMID, nothing to do */
2112                 if (semid == -1) {
2113                         rcu_read_unlock();
2114                         continue;
2115                 }
2116 
2117                 sma = sem_obtain_object_check(tsk->nsproxy->ipc_ns, semid);
2118                 /* exit_sem raced with IPC_RMID, nothing to do */
2119                 if (IS_ERR(sma)) {
2120                         rcu_read_unlock();
2121                         continue;
2122                 }
2123 
2124                 sem_lock(sma, NULL, -1);
2125                 /* exit_sem raced with IPC_RMID, nothing to do */
2126                 if (!ipc_valid_object(&sma->sem_perm)) {
2127                         sem_unlock(sma, -1);
2128                         rcu_read_unlock();
2129                         continue;
2130                 }
2131                 un = __lookup_undo(ulp, semid);
2132                 if (un == NULL) {
2133                         /* exit_sem raced with IPC_RMID+semget() that created
2134                          * exactly the same semid. Nothing to do.
2135                          */
2136                         sem_unlock(sma, -1);
2137                         rcu_read_unlock();
2138                         continue;
2139                 }
2140 
2141                 /* remove un from the linked lists */
2142                 ipc_assert_locked_object(&sma->sem_perm);
2143                 list_del(&un->list_id);
2144 
2145                 /* we are the last process using this ulp, acquiring ulp->lock
2146                  * isn't required. Besides that, we are also protected against
2147                  * IPC_RMID as we hold sma->sem_perm lock now
2148                  */
2149                 list_del_rcu(&un->list_proc);
2150 
2151                 /* perform adjustments registered in un */
2152                 for (i = 0; i < sma->sem_nsems; i++) {
2153                         struct sem *semaphore = &sma->sem_base[i];
2154                         if (un->semadj[i]) {
2155                                 semaphore->semval += un->semadj[i];
2156                                 /*
2157                                  * Range checks of the new semaphore value,
2158                                  * not defined by sus:
2159                                  * - Some unices ignore the undo entirely
2160                                  *   (e.g. HP UX 11i 11.22, Tru64 V5.1)
2161                                  * - some cap the value (e.g. FreeBSD caps
2162                                  *   at 0, but doesn't enforce SEMVMX)
2163                                  *
2164                                  * Linux caps the semaphore value, both at 0
2165                                  * and at SEMVMX.
2166                                  *
2167                                  *      Manfred <manfred@colorfullife.com>
2168                                  */
2169                                 if (semaphore->semval < 0)
2170                                         semaphore->semval = 0;
2171                                 if (semaphore->semval > SEMVMX)
2172                                         semaphore->semval = SEMVMX;
2173                                 semaphore->sempid = task_tgid_vnr(current);
2174                         }
2175                 }
2176                 /* maybe some queued-up processes were waiting for this */
2177                 INIT_LIST_HEAD(&tasks);
2178                 do_smart_update(sma, NULL, 0, 1, &tasks);
2179                 sem_unlock(sma, -1);
2180                 rcu_read_unlock();
2181                 wake_up_sem_queue_do(&tasks);
2182 
2183                 kfree_rcu(un, rcu);
2184         }
2185         kfree(ulp);
2186 }
2187 
2188 #ifdef CONFIG_PROC_FS
2189 static int sysvipc_sem_proc_show(struct seq_file *s, void *it)
2190 {
2191         struct user_namespace *user_ns = seq_user_ns(s);
2192         struct sem_array *sma = it;
2193         time_t sem_otime;
2194 
2195         /*
2196          * The proc interface isn't aware of sem_lock(), it calls
2197          * ipc_lock_object() directly (in sysvipc_find_ipc).
2198          * In order to stay compatible with sem_lock(), we must wait until
2199          * all simple semop() calls have left their critical regions.
2200          */
2201         sem_wait_array(sma);
2202 
2203         sem_otime = get_semotime(sma);
2204 
2205         seq_printf(s,
2206                    "%10d %10d  %4o %10u %5u %5u %5u %5u %10lu %10lu\n",
2207                    sma->sem_perm.key,
2208                    sma->sem_perm.id,
2209                    sma->sem_perm.mode,
2210                    sma->sem_nsems,
2211                    from_kuid_munged(user_ns, sma->sem_perm.uid),
2212                    from_kgid_munged(user_ns, sma->sem_perm.gid),
2213                    from_kuid_munged(user_ns, sma->sem_perm.cuid),
2214                    from_kgid_munged(user_ns, sma->sem_perm.cgid),
2215                    sem_otime,
2216                    sma->sem_ctime);
2217 
2218         return 0;
2219 }
2220 #endif
2221 

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