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

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