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

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