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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_semncnt() and
 51  *   count_semzcnt()
 52  * - the task that performs a successful semop() scans the list of all
 53  *   sleeping tasks and completes any pending operations that can be fulfilled.
 54  *   Semaphores are actively given to waiting tasks (necessary for FIFO).
 55  *   (see update_queue())
 56  * - To improve the scalability, the actual wake-up calls are performed after
 57  *   dropping all locks. (see wake_up_sem_queue_prepare(),
 58  *   wake_up_sem_queue_do())
 59  * - All work is done by the waker, the woken up task does not have to do
 60  *   anything - not even acquiring a lock or dropping a refcount.
 61  * - A woken up task may not even touch the semaphore array anymore, it may
 62  *   have been destroyed already by a semctl(RMID).
 63  * - The synchronizations between wake-ups due to a timeout/signal and a
 64  *   wake-up due to a completed semaphore operation is achieved by using an
 65  *   intermediate state (IN_WAKEUP).
 66  * - UNDO values are stored in an array (one per process and per
 67  *   semaphore array, lazily allocated). For backwards compatibility, multiple
 68  *   modes for the UNDO variables are supported (per process, per thread)
 69  *   (see copy_semundo, CLONE_SYSVSEM)
 70  * - There are two lists of the pending operations: a per-array list
 71  *   and per-semaphore list (stored in the array). This allows to achieve FIFO
 72  *   ordering without always scanning all pending operations.
 73  *   The worst-case behavior is nevertheless O(N^2) for N wakeups.
 74  */
 75 
 76 #include <linux/slab.h>
 77 #include <linux/spinlock.h>
 78 #include <linux/init.h>
 79 #include <linux/proc_fs.h>
 80 #include <linux/time.h>
 81 #include <linux/security.h>
 82 #include <linux/syscalls.h>
 83 #include <linux/audit.h>
 84 #include <linux/capability.h>
 85 #include <linux/seq_file.h>
 86 #include <linux/rwsem.h>
 87 #include <linux/nsproxy.h>
 88 #include <linux/ipc_namespace.h>
 89 
 90 #include <asm/uaccess.h>
 91 #include "util.h"
 92 
 93 /* One semaphore structure for each semaphore in the system. */
 94 struct sem {
 95         int     semval;         /* current value */
 96         int     sempid;         /* pid of last operation */
 97         spinlock_t      lock;   /* spinlock for fine-grained semtimedop */
 98         struct list_head pending_alter; /* pending single-sop operations */
 99                                         /* that alter the semaphore */
100         struct list_head pending_const; /* pending single-sop operations */
101                                         /* that do not alter the semaphore*/
102         time_t  sem_otime;      /* candidate for sem_otime */
103 } ____cacheline_aligned_in_smp;
104 
105 /* One queue for each sleeping process in the system. */
106 struct sem_queue {
107         struct list_head        list;    /* queue of pending operations */
108         struct task_struct      *sleeper; /* this process */
109         struct sem_undo         *undo;   /* undo structure */
110         int                     pid;     /* process id of requesting process */
111         int                     status;  /* completion status of operation */
112         struct sembuf           *sops;   /* array of pending operations */
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         id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni);
511         if (id < 0) {
512                 ipc_rcu_putref(sma, sem_rcu_free);
513                 return id;
514         }
515         ns->used_sems += nsems;
516 
517         sma->sem_base = (struct sem *) &sma[1];
518 
519         for (i = 0; i < nsems; i++) {
520                 INIT_LIST_HEAD(&sma->sem_base[i].pending_alter);
521                 INIT_LIST_HEAD(&sma->sem_base[i].pending_const);
522                 spin_lock_init(&sma->sem_base[i].lock);
523         }
524 
525         sma->complex_count = 0;
526         INIT_LIST_HEAD(&sma->pending_alter);
527         INIT_LIST_HEAD(&sma->pending_const);
528         INIT_LIST_HEAD(&sma->list_id);
529         sma->sem_nsems = nsems;
530         sma->sem_ctime = get_seconds();
531         sem_unlock(sma, -1);
532         rcu_read_unlock();
533 
534         return sma->sem_perm.id;
535 }
536 
537 
538 /*
539  * Called with sem_ids.rwsem and ipcp locked.
540  */
541 static inline int sem_security(struct kern_ipc_perm *ipcp, int semflg)
542 {
543         struct sem_array *sma;
544 
545         sma = container_of(ipcp, struct sem_array, sem_perm);
546         return security_sem_associate(sma, semflg);
547 }
548 
549 /*
550  * Called with sem_ids.rwsem and ipcp locked.
551  */
552 static inline int sem_more_checks(struct kern_ipc_perm *ipcp,
553                                 struct ipc_params *params)
554 {
555         struct sem_array *sma;
556 
557         sma = container_of(ipcp, struct sem_array, sem_perm);
558         if (params->u.nsems > sma->sem_nsems)
559                 return -EINVAL;
560 
561         return 0;
562 }
563 
564 SYSCALL_DEFINE3(semget, key_t, key, int, nsems, int, semflg)
565 {
566         struct ipc_namespace *ns;
567         struct ipc_ops sem_ops;
568         struct ipc_params sem_params;
569 
570         ns = current->nsproxy->ipc_ns;
571 
572         if (nsems < 0 || nsems > ns->sc_semmsl)
573                 return -EINVAL;
574 
575         sem_ops.getnew = newary;
576         sem_ops.associate = sem_security;
577         sem_ops.more_checks = sem_more_checks;
578 
579         sem_params.key = key;
580         sem_params.flg = semflg;
581         sem_params.u.nsems = nsems;
582 
583         return ipcget(ns, &sem_ids(ns), &sem_ops, &sem_params);
584 }
585 
586 /**
587  * perform_atomic_semop - Perform (if possible) a semaphore operation
588  * @sma: semaphore array
589  * @sops: array with operations that should be checked
590  * @nsops: number of operations
591  * @un: undo array
592  * @pid: pid that did the change
593  *
594  * Returns 0 if the operation was possible.
595  * Returns 1 if the operation is impossible, the caller must sleep.
596  * Negative values are error codes.
597  */
598 static int perform_atomic_semop(struct sem_array *sma, struct sembuf *sops,
599                              int nsops, struct sem_undo *un, int pid)
600 {
601         int result, sem_op;
602         struct sembuf *sop;
603         struct sem *curr;
604 
605         for (sop = sops; sop < sops + nsops; sop++) {
606                 curr = sma->sem_base + sop->sem_num;
607                 sem_op = sop->sem_op;
608                 result = curr->semval;
609 
610                 if (!sem_op && result)
611                         goto would_block;
612 
613                 result += sem_op;
614                 if (result < 0)
615                         goto would_block;
616                 if (result > SEMVMX)
617                         goto out_of_range;
618 
619                 if (sop->sem_flg & SEM_UNDO) {
620                         int undo = un->semadj[sop->sem_num] - sem_op;
621                         /* Exceeding the undo range is an error. */
622                         if (undo < (-SEMAEM - 1) || undo > SEMAEM)
623                                 goto out_of_range;
624                         un->semadj[sop->sem_num] = undo;
625                 }
626 
627                 curr->semval = result;
628         }
629 
630         sop--;
631         while (sop >= sops) {
632                 sma->sem_base[sop->sem_num].sempid = pid;
633                 sop--;
634         }
635 
636         return 0;
637 
638 out_of_range:
639         result = -ERANGE;
640         goto undo;
641 
642 would_block:
643         if (sop->sem_flg & IPC_NOWAIT)
644                 result = -EAGAIN;
645         else
646                 result = 1;
647 
648 undo:
649         sop--;
650         while (sop >= sops) {
651                 sem_op = sop->sem_op;
652                 sma->sem_base[sop->sem_num].semval -= sem_op;
653                 if (sop->sem_flg & SEM_UNDO)
654                         un->semadj[sop->sem_num] += sem_op;
655                 sop--;
656         }
657 
658         return result;
659 }
660 
661 /** wake_up_sem_queue_prepare(q, error): Prepare wake-up
662  * @q: queue entry that must be signaled
663  * @error: Error value for the signal
664  *
665  * Prepare the wake-up of the queue entry q.
666  */
667 static void wake_up_sem_queue_prepare(struct list_head *pt,
668                                 struct sem_queue *q, int error)
669 {
670         if (list_empty(pt)) {
671                 /*
672                  * Hold preempt off so that we don't get preempted and have the
673                  * wakee busy-wait until we're scheduled back on.
674                  */
675                 preempt_disable();
676         }
677         q->status = IN_WAKEUP;
678         q->pid = error;
679 
680         list_add_tail(&q->list, pt);
681 }
682 
683 /**
684  * wake_up_sem_queue_do - do the actual wake-up
685  * @pt: list of tasks to be woken up
686  *
687  * Do the actual wake-up.
688  * The function is called without any locks held, thus the semaphore array
689  * could be destroyed already and the tasks can disappear as soon as the
690  * status is set to the actual return code.
691  */
692 static void wake_up_sem_queue_do(struct list_head *pt)
693 {
694         struct sem_queue *q, *t;
695         int did_something;
696 
697         did_something = !list_empty(pt);
698         list_for_each_entry_safe(q, t, pt, list) {
699                 wake_up_process(q->sleeper);
700                 /* q can disappear immediately after writing q->status. */
701                 smp_wmb();
702                 q->status = q->pid;
703         }
704         if (did_something)
705                 preempt_enable();
706 }
707 
708 static void unlink_queue(struct sem_array *sma, struct sem_queue *q)
709 {
710         list_del(&q->list);
711         if (q->nsops > 1)
712                 sma->complex_count--;
713 }
714 
715 /** check_restart(sma, q)
716  * @sma: semaphore array
717  * @q: the operation that just completed
718  *
719  * update_queue is O(N^2) when it restarts scanning the whole queue of
720  * waiting operations. Therefore this function checks if the restart is
721  * really necessary. It is called after a previously waiting operation
722  * modified the array.
723  * Note that wait-for-zero operations are handled without restart.
724  */
725 static int check_restart(struct sem_array *sma, struct sem_queue *q)
726 {
727         /* pending complex alter operations are too difficult to analyse */
728         if (!list_empty(&sma->pending_alter))
729                 return 1;
730 
731         /* we were a sleeping complex operation. Too difficult */
732         if (q->nsops > 1)
733                 return 1;
734 
735         /* It is impossible that someone waits for the new value:
736          * - complex operations always restart.
737          * - wait-for-zero are handled seperately.
738          * - q is a previously sleeping simple operation that
739          *   altered the array. It must be a decrement, because
740          *   simple increments never sleep.
741          * - If there are older (higher priority) decrements
742          *   in the queue, then they have observed the original
743          *   semval value and couldn't proceed. The operation
744          *   decremented to value - thus they won't proceed either.
745          */
746         return 0;
747 }
748 
749 /**
750  * wake_const_ops - wake up non-alter tasks
751  * @sma: semaphore array.
752  * @semnum: semaphore that was modified.
753  * @pt: list head for the tasks that must be woken up.
754  *
755  * wake_const_ops must be called after a semaphore in a semaphore array
756  * was set to 0. If complex const operations are pending, wake_const_ops must
757  * be called with semnum = -1, as well as with the number of each modified
758  * semaphore.
759  * The tasks that must be woken up are added to @pt. The return code
760  * is stored in q->pid.
761  * The function returns 1 if at least one operation was completed successfully.
762  */
763 static int wake_const_ops(struct sem_array *sma, int semnum,
764                                 struct list_head *pt)
765 {
766         struct sem_queue *q;
767         struct list_head *walk;
768         struct list_head *pending_list;
769         int semop_completed = 0;
770 
771         if (semnum == -1)
772                 pending_list = &sma->pending_const;
773         else
774                 pending_list = &sma->sem_base[semnum].pending_const;
775 
776         walk = pending_list->next;
777         while (walk != pending_list) {
778                 int error;
779 
780                 q = container_of(walk, struct sem_queue, list);
781                 walk = walk->next;
782 
783                 error = perform_atomic_semop(sma, q->sops, q->nsops,
784                                                  q->undo, q->pid);
785 
786                 if (error <= 0) {
787                         /* operation completed, remove from queue & wakeup */
788 
789                         unlink_queue(sma, q);
790 
791                         wake_up_sem_queue_prepare(pt, q, error);
792                         if (error == 0)
793                                 semop_completed = 1;
794                 }
795         }
796         return semop_completed;
797 }
798 
799 /**
800  * do_smart_wakeup_zero - wakeup all wait for zero tasks
801  * @sma: semaphore array
802  * @sops: operations that were performed
803  * @nsops: number of operations
804  * @pt: list head of the tasks that must be woken up.
805  *
806  * Checks all required queue for wait-for-zero operations, based
807  * on the actual changes that were performed on the semaphore array.
808  * The function returns 1 if at least one operation was completed successfully.
809  */
810 static int do_smart_wakeup_zero(struct sem_array *sma, struct sembuf *sops,
811                                         int nsops, struct list_head *pt)
812 {
813         int i;
814         int semop_completed = 0;
815         int got_zero = 0;
816 
817         /* first: the per-semaphore queues, if known */
818         if (sops) {
819                 for (i = 0; i < nsops; i++) {
820                         int num = sops[i].sem_num;
821 
822                         if (sma->sem_base[num].semval == 0) {
823                                 got_zero = 1;
824                                 semop_completed |= wake_const_ops(sma, num, pt);
825                         }
826                 }
827         } else {
828                 /*
829                  * No sops means modified semaphores not known.
830                  * Assume all were changed.
831                  */
832                 for (i = 0; i < sma->sem_nsems; i++) {
833                         if (sma->sem_base[i].semval == 0) {
834                                 got_zero = 1;
835                                 semop_completed |= wake_const_ops(sma, i, pt);
836                         }
837                 }
838         }
839         /*
840          * If one of the modified semaphores got 0,
841          * then check the global queue, too.
842          */
843         if (got_zero)
844                 semop_completed |= wake_const_ops(sma, -1, pt);
845 
846         return semop_completed;
847 }
848 
849 
850 /**
851  * update_queue - look for tasks that can be completed.
852  * @sma: semaphore array.
853  * @semnum: semaphore that was modified.
854  * @pt: list head for the tasks that must be woken up.
855  *
856  * update_queue must be called after a semaphore in a semaphore array
857  * was modified. If multiple semaphores were modified, update_queue must
858  * be called with semnum = -1, as well as with the number of each modified
859  * semaphore.
860  * The tasks that must be woken up are added to @pt. The return code
861  * is stored in q->pid.
862  * The function internally checks if const operations can now succeed.
863  *
864  * The function return 1 if at least one semop was completed successfully.
865  */
866 static int update_queue(struct sem_array *sma, int semnum, struct list_head *pt)
867 {
868         struct sem_queue *q;
869         struct list_head *walk;
870         struct list_head *pending_list;
871         int semop_completed = 0;
872 
873         if (semnum == -1)
874                 pending_list = &sma->pending_alter;
875         else
876                 pending_list = &sma->sem_base[semnum].pending_alter;
877 
878 again:
879         walk = pending_list->next;
880         while (walk != pending_list) {
881                 int error, restart;
882 
883                 q = container_of(walk, struct sem_queue, list);
884                 walk = walk->next;
885 
886                 /* If we are scanning the single sop, per-semaphore list of
887                  * one semaphore and that semaphore is 0, then it is not
888                  * necessary to scan further: simple increments
889                  * that affect only one entry succeed immediately and cannot
890                  * be in the  per semaphore pending queue, and decrements
891                  * cannot be successful if the value is already 0.
892                  */
893                 if (semnum != -1 && sma->sem_base[semnum].semval == 0)
894                         break;
895 
896                 error = perform_atomic_semop(sma, q->sops, q->nsops,
897                                          q->undo, q->pid);
898 
899                 /* Does q->sleeper still need to sleep? */
900                 if (error > 0)
901                         continue;
902 
903                 unlink_queue(sma, q);
904 
905                 if (error) {
906                         restart = 0;
907                 } else {
908                         semop_completed = 1;
909                         do_smart_wakeup_zero(sma, q->sops, q->nsops, pt);
910                         restart = check_restart(sma, q);
911                 }
912 
913                 wake_up_sem_queue_prepare(pt, q, error);
914                 if (restart)
915                         goto again;
916         }
917         return semop_completed;
918 }
919 
920 /**
921  * set_semotime - set sem_otime
922  * @sma: semaphore array
923  * @sops: operations that modified the array, may be NULL
924  *
925  * sem_otime is replicated to avoid cache line trashing.
926  * This function sets one instance to the current time.
927  */
928 static void set_semotime(struct sem_array *sma, struct sembuf *sops)
929 {
930         if (sops == NULL) {
931                 sma->sem_base[0].sem_otime = get_seconds();
932         } else {
933                 sma->sem_base[sops[0].sem_num].sem_otime =
934                                                         get_seconds();
935         }
936 }
937 
938 /**
939  * do_smart_update - optimized update_queue
940  * @sma: semaphore array
941  * @sops: operations that were performed
942  * @nsops: number of operations
943  * @otime: force setting otime
944  * @pt: list head of the tasks that must be woken up.
945  *
946  * do_smart_update() does the required calls to update_queue and wakeup_zero,
947  * based on the actual changes that were performed on the semaphore array.
948  * Note that the function does not do the actual wake-up: the caller is
949  * responsible for calling wake_up_sem_queue_do(@pt).
950  * It is safe to perform this call after dropping all locks.
951  */
952 static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsops,
953                         int otime, struct list_head *pt)
954 {
955         int i;
956 
957         otime |= do_smart_wakeup_zero(sma, sops, nsops, pt);
958 
959         if (!list_empty(&sma->pending_alter)) {
960                 /* semaphore array uses the global queue - just process it. */
961                 otime |= update_queue(sma, -1, pt);
962         } else {
963                 if (!sops) {
964                         /*
965                          * No sops, thus the modified semaphores are not
966                          * known. Check all.
967                          */
968                         for (i = 0; i < sma->sem_nsems; i++)
969                                 otime |= update_queue(sma, i, pt);
970                 } else {
971                         /*
972                          * Check the semaphores that were increased:
973                          * - No complex ops, thus all sleeping ops are
974                          *   decrease.
975                          * - if we decreased the value, then any sleeping
976                          *   semaphore ops wont be able to run: If the
977                          *   previous value was too small, then the new
978                          *   value will be too small, too.
979                          */
980                         for (i = 0; i < nsops; i++) {
981                                 if (sops[i].sem_op > 0) {
982                                         otime |= update_queue(sma,
983                                                         sops[i].sem_num, pt);
984                                 }
985                         }
986                 }
987         }
988         if (otime)
989                 set_semotime(sma, sops);
990 }
991 
992 /* The following counts are associated to each semaphore:
993  *   semncnt        number of tasks waiting on semval being nonzero
994  *   semzcnt        number of tasks waiting on semval being zero
995  * This model assumes that a task waits on exactly one semaphore.
996  * Since semaphore operations are to be performed atomically, tasks actually
997  * wait on a whole sequence of semaphores simultaneously.
998  * The counts we return here are a rough approximation, but still
999  * warrant that semncnt+semzcnt>0 if the task is on the pending queue.
1000  */
1001 static int count_semncnt(struct sem_array *sma, ushort semnum)
1002 {
1003         int semncnt;
1004         struct sem_queue *q;
1005 
1006         semncnt = 0;
1007         list_for_each_entry(q, &sma->sem_base[semnum].pending_alter, list) {
1008                 struct sembuf *sops = q->sops;
1009                 BUG_ON(sops->sem_num != semnum);
1010                 if ((sops->sem_op < 0) && !(sops->sem_flg & IPC_NOWAIT))
1011                         semncnt++;
1012         }
1013 
1014         list_for_each_entry(q, &sma->pending_alter, list) {
1015                 struct sembuf *sops = q->sops;
1016                 int nsops = q->nsops;
1017                 int i;
1018                 for (i = 0; i < nsops; i++)
1019                         if (sops[i].sem_num == semnum
1020                             && (sops[i].sem_op < 0)
1021                             && !(sops[i].sem_flg & IPC_NOWAIT))
1022                                 semncnt++;
1023         }
1024         return semncnt;
1025 }
1026 
1027 static int count_semzcnt(struct sem_array *sma, ushort semnum)
1028 {
1029         int semzcnt;
1030         struct sem_queue *q;
1031 
1032         semzcnt = 0;
1033         list_for_each_entry(q, &sma->sem_base[semnum].pending_const, list) {
1034                 struct sembuf *sops = q->sops;
1035                 BUG_ON(sops->sem_num != semnum);
1036                 if ((sops->sem_op == 0) && !(sops->sem_flg & IPC_NOWAIT))
1037                         semzcnt++;
1038         }
1039 
1040         list_for_each_entry(q, &sma->pending_const, list) {
1041                 struct sembuf *sops = q->sops;
1042                 int nsops = q->nsops;
1043                 int i;
1044                 for (i = 0; i < nsops; i++)
1045                         if (sops[i].sem_num == semnum
1046                             && (sops[i].sem_op == 0)
1047                             && !(sops[i].sem_flg & IPC_NOWAIT))
1048                                 semzcnt++;
1049         }
1050         return semzcnt;
1051 }
1052 
1053 /* Free a semaphore set. freeary() is called with sem_ids.rwsem locked
1054  * as a writer and the spinlock for this semaphore set hold. sem_ids.rwsem
1055  * remains locked on exit.
1056  */
1057 static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
1058 {
1059         struct sem_undo *un, *tu;
1060         struct sem_queue *q, *tq;
1061         struct sem_array *sma = container_of(ipcp, struct sem_array, sem_perm);
1062         struct list_head tasks;
1063         int i;
1064 
1065         /* Free the existing undo structures for this semaphore set.  */
1066         ipc_assert_locked_object(&sma->sem_perm);
1067         list_for_each_entry_safe(un, tu, &sma->list_id, list_id) {
1068                 list_del(&un->list_id);
1069                 spin_lock(&un->ulp->lock);
1070                 un->semid = -1;
1071                 list_del_rcu(&un->list_proc);
1072                 spin_unlock(&un->ulp->lock);
1073                 kfree_rcu(un, rcu);
1074         }
1075 
1076         /* Wake up all pending processes and let them fail with EIDRM. */
1077         INIT_LIST_HEAD(&tasks);
1078         list_for_each_entry_safe(q, tq, &sma->pending_const, list) {
1079                 unlink_queue(sma, q);
1080                 wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
1081         }
1082 
1083         list_for_each_entry_safe(q, tq, &sma->pending_alter, list) {
1084                 unlink_queue(sma, q);
1085                 wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
1086         }
1087         for (i = 0; i < sma->sem_nsems; i++) {
1088                 struct sem *sem = sma->sem_base + i;
1089                 list_for_each_entry_safe(q, tq, &sem->pending_const, list) {
1090                         unlink_queue(sma, q);
1091                         wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
1092                 }
1093                 list_for_each_entry_safe(q, tq, &sem->pending_alter, list) {
1094                         unlink_queue(sma, q);
1095                         wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
1096                 }
1097         }
1098 
1099         /* Remove the semaphore set from the IDR */
1100         sem_rmid(ns, sma);
1101         sem_unlock(sma, -1);
1102         rcu_read_unlock();
1103 
1104         wake_up_sem_queue_do(&tasks);
1105         ns->used_sems -= sma->sem_nsems;
1106         ipc_rcu_putref(sma, sem_rcu_free);
1107 }
1108 
1109 static unsigned long copy_semid_to_user(void __user *buf, struct semid64_ds *in, int version)
1110 {
1111         switch (version) {
1112         case IPC_64:
1113                 return copy_to_user(buf, in, sizeof(*in));
1114         case IPC_OLD:
1115             {
1116                 struct semid_ds out;
1117 
1118                 memset(&out, 0, sizeof(out));
1119 
1120                 ipc64_perm_to_ipc_perm(&in->sem_perm, &out.sem_perm);
1121 
1122                 out.sem_otime   = in->sem_otime;
1123                 out.sem_ctime   = in->sem_ctime;
1124                 out.sem_nsems   = in->sem_nsems;
1125 
1126                 return copy_to_user(buf, &out, sizeof(out));
1127             }
1128         default:
1129                 return -EINVAL;
1130         }
1131 }
1132 
1133 static time_t get_semotime(struct sem_array *sma)
1134 {
1135         int i;
1136         time_t res;
1137 
1138         res = sma->sem_base[0].sem_otime;
1139         for (i = 1; i < sma->sem_nsems; i++) {
1140                 time_t to = sma->sem_base[i].sem_otime;
1141 
1142                 if (to > res)
1143                         res = to;
1144         }
1145         return res;
1146 }
1147 
1148 static int semctl_nolock(struct ipc_namespace *ns, int semid,
1149                          int cmd, int version, void __user *p)
1150 {
1151         int err;
1152         struct sem_array *sma;
1153 
1154         switch (cmd) {
1155         case IPC_INFO:
1156         case SEM_INFO:
1157         {
1158                 struct seminfo seminfo;
1159                 int max_id;
1160 
1161                 err = security_sem_semctl(NULL, cmd);
1162                 if (err)
1163                         return err;
1164                 
1165                 memset(&seminfo, 0, sizeof(seminfo));
1166                 seminfo.semmni = ns->sc_semmni;
1167                 seminfo.semmns = ns->sc_semmns;
1168                 seminfo.semmsl = ns->sc_semmsl;
1169                 seminfo.semopm = ns->sc_semopm;
1170                 seminfo.semvmx = SEMVMX;
1171                 seminfo.semmnu = SEMMNU;
1172                 seminfo.semmap = SEMMAP;
1173                 seminfo.semume = SEMUME;
1174                 down_read(&sem_ids(ns).rwsem);
1175                 if (cmd == SEM_INFO) {
1176                         seminfo.semusz = sem_ids(ns).in_use;
1177                         seminfo.semaem = ns->used_sems;
1178                 } else {
1179                         seminfo.semusz = SEMUSZ;
1180                         seminfo.semaem = SEMAEM;
1181                 }
1182                 max_id = ipc_get_maxid(&sem_ids(ns));
1183                 up_read(&sem_ids(ns).rwsem);
1184                 if (copy_to_user(p, &seminfo, sizeof(struct seminfo))) 
1185                         return -EFAULT;
1186                 return (max_id < 0) ? 0 : max_id;
1187         }
1188         case IPC_STAT:
1189         case SEM_STAT:
1190         {
1191                 struct semid64_ds tbuf;
1192                 int id = 0;
1193 
1194                 memset(&tbuf, 0, sizeof(tbuf));
1195 
1196                 rcu_read_lock();
1197                 if (cmd == SEM_STAT) {
1198                         sma = sem_obtain_object(ns, semid);
1199                         if (IS_ERR(sma)) {
1200                                 err = PTR_ERR(sma);
1201                                 goto out_unlock;
1202                         }
1203                         id = sma->sem_perm.id;
1204                 } else {
1205                         sma = sem_obtain_object_check(ns, semid);
1206                         if (IS_ERR(sma)) {
1207                                 err = PTR_ERR(sma);
1208                                 goto out_unlock;
1209                         }
1210                 }
1211 
1212                 err = -EACCES;
1213                 if (ipcperms(ns, &sma->sem_perm, S_IRUGO))
1214                         goto out_unlock;
1215 
1216                 err = security_sem_semctl(sma, cmd);
1217                 if (err)
1218                         goto out_unlock;
1219 
1220                 kernel_to_ipc64_perm(&sma->sem_perm, &tbuf.sem_perm);
1221                 tbuf.sem_otime = get_semotime(sma);
1222                 tbuf.sem_ctime = sma->sem_ctime;
1223                 tbuf.sem_nsems = sma->sem_nsems;
1224                 rcu_read_unlock();
1225                 if (copy_semid_to_user(p, &tbuf, version))
1226                         return -EFAULT;
1227                 return id;
1228         }
1229         default:
1230                 return -EINVAL;
1231         }
1232 out_unlock:
1233         rcu_read_unlock();
1234         return err;
1235 }
1236 
1237 static int semctl_setval(struct ipc_namespace *ns, int semid, int semnum,
1238                 unsigned long arg)
1239 {
1240         struct sem_undo *un;
1241         struct sem_array *sma;
1242         struct sem *curr;
1243         int err;
1244         struct list_head tasks;
1245         int val;
1246 #if defined(CONFIG_64BIT) && defined(__BIG_ENDIAN)
1247         /* big-endian 64bit */
1248         val = arg >> 32;
1249 #else
1250         /* 32bit or little-endian 64bit */
1251         val = arg;
1252 #endif
1253 
1254         if (val > SEMVMX || val < 0)
1255                 return -ERANGE;
1256 
1257         INIT_LIST_HEAD(&tasks);
1258 
1259         rcu_read_lock();
1260         sma = sem_obtain_object_check(ns, semid);
1261         if (IS_ERR(sma)) {
1262                 rcu_read_unlock();
1263                 return PTR_ERR(sma);
1264         }
1265 
1266         if (semnum < 0 || semnum >= sma->sem_nsems) {
1267                 rcu_read_unlock();
1268                 return -EINVAL;
1269         }
1270 
1271 
1272         if (ipcperms(ns, &sma->sem_perm, S_IWUGO)) {
1273                 rcu_read_unlock();
1274                 return -EACCES;
1275         }
1276 
1277         err = security_sem_semctl(sma, SETVAL);
1278         if (err) {
1279                 rcu_read_unlock();
1280                 return -EACCES;
1281         }
1282 
1283         sem_lock(sma, NULL, -1);
1284 
1285         if (!ipc_valid_object(&sma->sem_perm)) {
1286                 sem_unlock(sma, -1);
1287                 rcu_read_unlock();
1288                 return -EIDRM;
1289         }
1290 
1291         curr = &sma->sem_base[semnum];
1292 
1293         ipc_assert_locked_object(&sma->sem_perm);
1294         list_for_each_entry(un, &sma->list_id, list_id)
1295                 un->semadj[semnum] = 0;
1296 
1297         curr->semval = val;
1298         curr->sempid = task_tgid_vnr(current);
1299         sma->sem_ctime = get_seconds();
1300         /* maybe some queued-up processes were waiting for this */
1301         do_smart_update(sma, NULL, 0, 0, &tasks);
1302         sem_unlock(sma, -1);
1303         rcu_read_unlock();
1304         wake_up_sem_queue_do(&tasks);
1305         return 0;
1306 }
1307 
1308 static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
1309                 int cmd, void __user *p)
1310 {
1311         struct sem_array *sma;
1312         struct sem *curr;
1313         int err, nsems;
1314         ushort fast_sem_io[SEMMSL_FAST];
1315         ushort *sem_io = fast_sem_io;
1316         struct list_head tasks;
1317 
1318         INIT_LIST_HEAD(&tasks);
1319 
1320         rcu_read_lock();
1321         sma = sem_obtain_object_check(ns, semid);
1322         if (IS_ERR(sma)) {
1323                 rcu_read_unlock();
1324                 return PTR_ERR(sma);
1325         }
1326 
1327         nsems = sma->sem_nsems;
1328 
1329         err = -EACCES;
1330         if (ipcperms(ns, &sma->sem_perm, cmd == SETALL ? S_IWUGO : S_IRUGO))
1331                 goto out_rcu_wakeup;
1332 
1333         err = security_sem_semctl(sma, cmd);
1334         if (err)
1335                 goto out_rcu_wakeup;
1336 
1337         err = -EACCES;
1338         switch (cmd) {
1339         case GETALL:
1340         {
1341                 ushort __user *array = p;
1342                 int i;
1343 
1344                 sem_lock(sma, NULL, -1);
1345                 if (!ipc_valid_object(&sma->sem_perm)) {
1346                         err = -EIDRM;
1347                         goto out_unlock;
1348                 }
1349                 if (nsems > SEMMSL_FAST) {
1350                         if (!ipc_rcu_getref(sma)) {
1351                                 err = -EIDRM;
1352                                 goto out_unlock;
1353                         }
1354                         sem_unlock(sma, -1);
1355                         rcu_read_unlock();
1356                         sem_io = ipc_alloc(sizeof(ushort)*nsems);
1357                         if (sem_io == NULL) {
1358                                 ipc_rcu_putref(sma, ipc_rcu_free);
1359                                 return -ENOMEM;
1360                         }
1361 
1362                         rcu_read_lock();
1363                         sem_lock_and_putref(sma);
1364                         if (!ipc_valid_object(&sma->sem_perm)) {
1365                                 err = -EIDRM;
1366                                 goto out_unlock;
1367                         }
1368                 }
1369                 for (i = 0; i < sma->sem_nsems; i++)
1370                         sem_io[i] = sma->sem_base[i].semval;
1371                 sem_unlock(sma, -1);
1372                 rcu_read_unlock();
1373                 err = 0;
1374                 if (copy_to_user(array, sem_io, nsems*sizeof(ushort)))
1375                         err = -EFAULT;
1376                 goto out_free;
1377         }
1378         case SETALL:
1379         {
1380                 int i;
1381                 struct sem_undo *un;
1382 
1383                 if (!ipc_rcu_getref(sma)) {
1384                         err = -EIDRM;
1385                         goto out_rcu_wakeup;
1386                 }
1387                 rcu_read_unlock();
1388 
1389                 if (nsems > SEMMSL_FAST) {
1390                         sem_io = ipc_alloc(sizeof(ushort)*nsems);
1391                         if (sem_io == NULL) {
1392                                 ipc_rcu_putref(sma, ipc_rcu_free);
1393                                 return -ENOMEM;
1394                         }
1395                 }
1396 
1397                 if (copy_from_user(sem_io, p, nsems*sizeof(ushort))) {
1398                         ipc_rcu_putref(sma, ipc_rcu_free);
1399                         err = -EFAULT;
1400                         goto out_free;
1401                 }
1402 
1403                 for (i = 0; i < nsems; i++) {
1404                         if (sem_io[i] > SEMVMX) {
1405                                 ipc_rcu_putref(sma, ipc_rcu_free);
1406                                 err = -ERANGE;
1407                                 goto out_free;
1408                         }
1409                 }
1410                 rcu_read_lock();
1411                 sem_lock_and_putref(sma);
1412                 if (!ipc_valid_object(&sma->sem_perm)) {
1413                         err = -EIDRM;
1414                         goto out_unlock;
1415                 }
1416 
1417                 for (i = 0; i < nsems; i++)
1418                         sma->sem_base[i].semval = sem_io[i];
1419 
1420                 ipc_assert_locked_object(&sma->sem_perm);
1421                 list_for_each_entry(un, &sma->list_id, list_id) {
1422                         for (i = 0; i < nsems; i++)
1423                                 un->semadj[i] = 0;
1424                 }
1425                 sma->sem_ctime = get_seconds();
1426                 /* maybe some queued-up processes were waiting for this */
1427                 do_smart_update(sma, NULL, 0, 0, &tasks);
1428                 err = 0;
1429                 goto out_unlock;
1430         }
1431         /* GETVAL, GETPID, GETNCTN, GETZCNT: fall-through */
1432         }
1433         err = -EINVAL;
1434         if (semnum < 0 || semnum >= nsems)
1435                 goto out_rcu_wakeup;
1436 
1437         sem_lock(sma, NULL, -1);
1438         if (!ipc_valid_object(&sma->sem_perm)) {
1439                 err = -EIDRM;
1440                 goto out_unlock;
1441         }
1442         curr = &sma->sem_base[semnum];
1443 
1444         switch (cmd) {
1445         case GETVAL:
1446                 err = curr->semval;
1447                 goto out_unlock;
1448         case GETPID:
1449                 err = curr->sempid;
1450                 goto out_unlock;
1451         case GETNCNT:
1452                 err = count_semncnt(sma, semnum);
1453                 goto out_unlock;
1454         case GETZCNT:
1455                 err = count_semzcnt(sma, semnum);
1456                 goto out_unlock;
1457         }
1458 
1459 out_unlock:
1460         sem_unlock(sma, -1);
1461 out_rcu_wakeup:
1462         rcu_read_unlock();
1463         wake_up_sem_queue_do(&tasks);
1464 out_free:
1465         if (sem_io != fast_sem_io)
1466                 ipc_free(sem_io, sizeof(ushort)*nsems);
1467         return err;
1468 }
1469 
1470 static inline unsigned long
1471 copy_semid_from_user(struct semid64_ds *out, void __user *buf, int version)
1472 {
1473         switch (version) {
1474         case IPC_64:
1475                 if (copy_from_user(out, buf, sizeof(*out)))
1476                         return -EFAULT;
1477                 return 0;
1478         case IPC_OLD:
1479             {
1480                 struct semid_ds tbuf_old;
1481 
1482                 if (copy_from_user(&tbuf_old, buf, sizeof(tbuf_old)))
1483                         return -EFAULT;
1484 
1485                 out->sem_perm.uid       = tbuf_old.sem_perm.uid;
1486                 out->sem_perm.gid       = tbuf_old.sem_perm.gid;
1487                 out->sem_perm.mode      = tbuf_old.sem_perm.mode;
1488 
1489                 return 0;
1490             }
1491         default:
1492                 return -EINVAL;
1493         }
1494 }
1495 
1496 /*
1497  * This function handles some semctl commands which require the rwsem
1498  * to be held in write mode.
1499  * NOTE: no locks must be held, the rwsem is taken inside this function.
1500  */
1501 static int semctl_down(struct ipc_namespace *ns, int semid,
1502                        int cmd, int version, void __user *p)
1503 {
1504         struct sem_array *sma;
1505         int err;
1506         struct semid64_ds semid64;
1507         struct kern_ipc_perm *ipcp;
1508 
1509         if (cmd == IPC_SET) {
1510                 if (copy_semid_from_user(&semid64, p, version))
1511                         return -EFAULT;
1512         }
1513 
1514         down_write(&sem_ids(ns).rwsem);
1515         rcu_read_lock();
1516 
1517         ipcp = ipcctl_pre_down_nolock(ns, &sem_ids(ns), semid, cmd,
1518                                       &semid64.sem_perm, 0);
1519         if (IS_ERR(ipcp)) {
1520                 err = PTR_ERR(ipcp);
1521                 goto out_unlock1;
1522         }
1523 
1524         sma = container_of(ipcp, struct sem_array, sem_perm);
1525 
1526         err = security_sem_semctl(sma, cmd);
1527         if (err)
1528                 goto out_unlock1;
1529 
1530         switch (cmd) {
1531         case IPC_RMID:
1532                 sem_lock(sma, NULL, -1);
1533                 /* freeary unlocks the ipc object and rcu */
1534                 freeary(ns, ipcp);
1535                 goto out_up;
1536         case IPC_SET:
1537                 sem_lock(sma, NULL, -1);
1538                 err = ipc_update_perm(&semid64.sem_perm, ipcp);
1539                 if (err)
1540                         goto out_unlock0;
1541                 sma->sem_ctime = get_seconds();
1542                 break;
1543         default:
1544                 err = -EINVAL;
1545                 goto out_unlock1;
1546         }
1547 
1548 out_unlock0:
1549         sem_unlock(sma, -1);
1550 out_unlock1:
1551         rcu_read_unlock();
1552 out_up:
1553         up_write(&sem_ids(ns).rwsem);
1554         return err;
1555 }
1556 
1557 SYSCALL_DEFINE4(semctl, int, semid, int, semnum, int, cmd, unsigned long, arg)
1558 {
1559         int version;
1560         struct ipc_namespace *ns;
1561         void __user *p = (void __user *)arg;
1562 
1563         if (semid < 0)
1564                 return -EINVAL;
1565 
1566         version = ipc_parse_version(&cmd);
1567         ns = current->nsproxy->ipc_ns;
1568 
1569         switch (cmd) {
1570         case IPC_INFO:
1571         case SEM_INFO:
1572         case IPC_STAT:
1573         case SEM_STAT:
1574                 return semctl_nolock(ns, semid, cmd, version, p);
1575         case GETALL:
1576         case GETVAL:
1577         case GETPID:
1578         case GETNCNT:
1579         case GETZCNT:
1580         case SETALL:
1581                 return semctl_main(ns, semid, semnum, cmd, p);
1582         case SETVAL:
1583                 return semctl_setval(ns, semid, semnum, arg);
1584         case IPC_RMID:
1585         case IPC_SET:
1586                 return semctl_down(ns, semid, cmd, version, p);
1587         default:
1588                 return -EINVAL;
1589         }
1590 }
1591 
1592 /* If the task doesn't already have a undo_list, then allocate one
1593  * here.  We guarantee there is only one thread using this undo list,
1594  * and current is THE ONE
1595  *
1596  * If this allocation and assignment succeeds, but later
1597  * portions of this code fail, there is no need to free the sem_undo_list.
1598  * Just let it stay associated with the task, and it'll be freed later
1599  * at exit time.
1600  *
1601  * This can block, so callers must hold no locks.
1602  */
1603 static inline int get_undo_list(struct sem_undo_list **undo_listp)
1604 {
1605         struct sem_undo_list *undo_list;
1606 
1607         undo_list = current->sysvsem.undo_list;
1608         if (!undo_list) {
1609                 undo_list = kzalloc(sizeof(*undo_list), GFP_KERNEL);
1610                 if (undo_list == NULL)
1611                         return -ENOMEM;
1612                 spin_lock_init(&undo_list->lock);
1613                 atomic_set(&undo_list->refcnt, 1);
1614                 INIT_LIST_HEAD(&undo_list->list_proc);
1615 
1616                 current->sysvsem.undo_list = undo_list;
1617         }
1618         *undo_listp = undo_list;
1619         return 0;
1620 }
1621 
1622 static struct sem_undo *__lookup_undo(struct sem_undo_list *ulp, int semid)
1623 {
1624         struct sem_undo *un;
1625 
1626         list_for_each_entry_rcu(un, &ulp->list_proc, list_proc) {
1627                 if (un->semid == semid)
1628                         return un;
1629         }
1630         return NULL;
1631 }
1632 
1633 static struct sem_undo *lookup_undo(struct sem_undo_list *ulp, int semid)
1634 {
1635         struct sem_undo *un;
1636 
1637         assert_spin_locked(&ulp->lock);
1638 
1639         un = __lookup_undo(ulp, semid);
1640         if (un) {
1641                 list_del_rcu(&un->list_proc);
1642                 list_add_rcu(&un->list_proc, &ulp->list_proc);
1643         }
1644         return un;
1645 }
1646 
1647 /**
1648  * find_alloc_undo - lookup (and if not present create) undo array
1649  * @ns: namespace
1650  * @semid: semaphore array id
1651  *
1652  * The function looks up (and if not present creates) the undo structure.
1653  * The size of the undo structure depends on the size of the semaphore
1654  * array, thus the alloc path is not that straightforward.
1655  * Lifetime-rules: sem_undo is rcu-protected, on success, the function
1656  * performs a rcu_read_lock().
1657  */
1658 static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
1659 {
1660         struct sem_array *sma;
1661         struct sem_undo_list *ulp;
1662         struct sem_undo *un, *new;
1663         int nsems, error;
1664 
1665         error = get_undo_list(&ulp);
1666         if (error)
1667                 return ERR_PTR(error);
1668 
1669         rcu_read_lock();
1670         spin_lock(&ulp->lock);
1671         un = lookup_undo(ulp, semid);
1672         spin_unlock(&ulp->lock);
1673         if (likely(un != NULL))
1674                 goto out;
1675 
1676         /* no undo structure around - allocate one. */
1677         /* step 1: figure out the size of the semaphore array */
1678         sma = sem_obtain_object_check(ns, semid);
1679         if (IS_ERR(sma)) {
1680                 rcu_read_unlock();
1681                 return ERR_CAST(sma);
1682         }
1683 
1684         nsems = sma->sem_nsems;
1685         if (!ipc_rcu_getref(sma)) {
1686                 rcu_read_unlock();
1687                 un = ERR_PTR(-EIDRM);
1688                 goto out;
1689         }
1690         rcu_read_unlock();
1691 
1692         /* step 2: allocate new undo structure */
1693         new = kzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems, GFP_KERNEL);
1694         if (!new) {
1695                 ipc_rcu_putref(sma, ipc_rcu_free);
1696                 return ERR_PTR(-ENOMEM);
1697         }
1698 
1699         /* step 3: Acquire the lock on semaphore array */
1700         rcu_read_lock();
1701         sem_lock_and_putref(sma);
1702         if (!ipc_valid_object(&sma->sem_perm)) {
1703                 sem_unlock(sma, -1);
1704                 rcu_read_unlock();
1705                 kfree(new);
1706                 un = ERR_PTR(-EIDRM);
1707                 goto out;
1708         }
1709         spin_lock(&ulp->lock);
1710 
1711         /*
1712          * step 4: check for races: did someone else allocate the undo struct?
1713          */
1714         un = lookup_undo(ulp, semid);
1715         if (un) {
1716                 kfree(new);
1717                 goto success;
1718         }
1719         /* step 5: initialize & link new undo structure */
1720         new->semadj = (short *) &new[1];
1721         new->ulp = ulp;
1722         new->semid = semid;
1723         assert_spin_locked(&ulp->lock);
1724         list_add_rcu(&new->list_proc, &ulp->list_proc);
1725         ipc_assert_locked_object(&sma->sem_perm);
1726         list_add(&new->list_id, &sma->list_id);
1727         un = new;
1728 
1729 success:
1730         spin_unlock(&ulp->lock);
1731         sem_unlock(sma, -1);
1732 out:
1733         return un;
1734 }
1735 
1736 
1737 /**
1738  * get_queue_result - retrieve the result code from sem_queue
1739  * @q: Pointer to queue structure
1740  *
1741  * Retrieve the return code from the pending queue. If IN_WAKEUP is found in
1742  * q->status, then we must loop until the value is replaced with the final
1743  * value: This may happen if a task is woken up by an unrelated event (e.g.
1744  * signal) and in parallel the task is woken up by another task because it got
1745  * the requested semaphores.
1746  *
1747  * The function can be called with or without holding the semaphore spinlock.
1748  */
1749 static int get_queue_result(struct sem_queue *q)
1750 {
1751         int error;
1752 
1753         error = q->status;
1754         while (unlikely(error == IN_WAKEUP)) {
1755                 cpu_relax();
1756                 error = q->status;
1757         }
1758 
1759         return error;
1760 }
1761 
1762 SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
1763                 unsigned, nsops, const struct timespec __user *, timeout)
1764 {
1765         int error = -EINVAL;
1766         struct sem_array *sma;
1767         struct sembuf fast_sops[SEMOPM_FAST];
1768         struct sembuf *sops = fast_sops, *sop;
1769         struct sem_undo *un;
1770         int undos = 0, alter = 0, max, locknum;
1771         struct sem_queue queue;
1772         unsigned long jiffies_left = 0;
1773         struct ipc_namespace *ns;
1774         struct list_head tasks;
1775 
1776         ns = current->nsproxy->ipc_ns;
1777 
1778         if (nsops < 1 || semid < 0)
1779                 return -EINVAL;
1780         if (nsops > ns->sc_semopm)
1781                 return -E2BIG;
1782         if (nsops > SEMOPM_FAST) {
1783                 sops = kmalloc(sizeof(*sops)*nsops, GFP_KERNEL);
1784                 if (sops == NULL)
1785                         return -ENOMEM;
1786         }
1787         if (copy_from_user(sops, tsops, nsops * sizeof(*tsops))) {
1788                 error =  -EFAULT;
1789                 goto out_free;
1790         }
1791         if (timeout) {
1792                 struct timespec _timeout;
1793                 if (copy_from_user(&_timeout, timeout, sizeof(*timeout))) {
1794                         error = -EFAULT;
1795                         goto out_free;
1796                 }
1797                 if (_timeout.tv_sec < 0 || _timeout.tv_nsec < 0 ||
1798                         _timeout.tv_nsec >= 1000000000L) {
1799                         error = -EINVAL;
1800                         goto out_free;
1801                 }
1802                 jiffies_left = timespec_to_jiffies(&_timeout);
1803         }
1804         max = 0;
1805         for (sop = sops; sop < sops + nsops; sop++) {
1806                 if (sop->sem_num >= max)
1807                         max = sop->sem_num;
1808                 if (sop->sem_flg & SEM_UNDO)
1809                         undos = 1;
1810                 if (sop->sem_op != 0)
1811                         alter = 1;
1812         }
1813 
1814         INIT_LIST_HEAD(&tasks);
1815 
1816         if (undos) {
1817                 /* On success, find_alloc_undo takes the rcu_read_lock */
1818                 un = find_alloc_undo(ns, semid);
1819                 if (IS_ERR(un)) {
1820                         error = PTR_ERR(un);
1821                         goto out_free;
1822                 }
1823         } else {
1824                 un = NULL;
1825                 rcu_read_lock();
1826         }
1827 
1828         sma = sem_obtain_object_check(ns, semid);
1829         if (IS_ERR(sma)) {
1830                 rcu_read_unlock();
1831                 error = PTR_ERR(sma);
1832                 goto out_free;
1833         }
1834 
1835         error = -EFBIG;
1836         if (max >= sma->sem_nsems)
1837                 goto out_rcu_wakeup;
1838 
1839         error = -EACCES;
1840         if (ipcperms(ns, &sma->sem_perm, alter ? S_IWUGO : S_IRUGO))
1841                 goto out_rcu_wakeup;
1842 
1843         error = security_sem_semop(sma, sops, nsops, alter);
1844         if (error)
1845                 goto out_rcu_wakeup;
1846 
1847         error = -EIDRM;
1848         locknum = sem_lock(sma, sops, nsops);
1849         /*
1850          * We eventually might perform the following check in a lockless
1851          * fashion, considering ipc_valid_object() locking constraints.
1852          * If nsops == 1 and there is no contention for sem_perm.lock, then
1853          * only a per-semaphore lock is held and it's OK to proceed with the
1854          * check below. More details on the fine grained locking scheme
1855          * entangled here and why it's RMID race safe on comments at sem_lock()
1856          */
1857         if (!ipc_valid_object(&sma->sem_perm))
1858                 goto out_unlock_free;
1859         /*
1860          * semid identifiers are not unique - find_alloc_undo may have
1861          * allocated an undo structure, it was invalidated by an RMID
1862          * and now a new array with received the same id. Check and fail.
1863          * This case can be detected checking un->semid. The existence of
1864          * "un" itself is guaranteed by rcu.
1865          */
1866         if (un && un->semid == -1)
1867                 goto out_unlock_free;
1868 
1869         error = perform_atomic_semop(sma, sops, nsops, un,
1870                                         task_tgid_vnr(current));
1871         if (error == 0) {
1872                 /* If the operation was successful, then do
1873                  * the required updates.
1874                  */
1875                 if (alter)
1876                         do_smart_update(sma, sops, nsops, 1, &tasks);
1877                 else
1878                         set_semotime(sma, sops);
1879         }
1880         if (error <= 0)
1881                 goto out_unlock_free;
1882 
1883         /* We need to sleep on this operation, so we put the current
1884          * task into the pending queue and go to sleep.
1885          */
1886                 
1887         queue.sops = sops;
1888         queue.nsops = nsops;
1889         queue.undo = un;
1890         queue.pid = task_tgid_vnr(current);
1891         queue.alter = alter;
1892 
1893         if (nsops == 1) {
1894                 struct sem *curr;
1895                 curr = &sma->sem_base[sops->sem_num];
1896 
1897                 if (alter) {
1898                         if (sma->complex_count) {
1899                                 list_add_tail(&queue.list,
1900                                                 &sma->pending_alter);
1901                         } else {
1902 
1903                                 list_add_tail(&queue.list,
1904                                                 &curr->pending_alter);
1905                         }
1906                 } else {
1907                         list_add_tail(&queue.list, &curr->pending_const);
1908                 }
1909         } else {
1910                 if (!sma->complex_count)
1911                         merge_queues(sma);
1912 
1913                 if (alter)
1914                         list_add_tail(&queue.list, &sma->pending_alter);
1915                 else
1916                         list_add_tail(&queue.list, &sma->pending_const);
1917 
1918                 sma->complex_count++;
1919         }
1920 
1921         queue.status = -EINTR;
1922         queue.sleeper = current;
1923 
1924 sleep_again:
1925         current->state = TASK_INTERRUPTIBLE;
1926         sem_unlock(sma, locknum);
1927         rcu_read_unlock();
1928 
1929         if (timeout)
1930                 jiffies_left = schedule_timeout(jiffies_left);
1931         else
1932                 schedule();
1933 
1934         error = get_queue_result(&queue);
1935 
1936         if (error != -EINTR) {
1937                 /* fast path: update_queue already obtained all requested
1938                  * resources.
1939                  * Perform a smp_mb(): User space could assume that semop()
1940                  * is a memory barrier: Without the mb(), the cpu could
1941                  * speculatively read in user space stale data that was
1942                  * overwritten by the previous owner of the semaphore.
1943                  */
1944                 smp_mb();
1945 
1946                 goto out_free;
1947         }
1948 
1949         rcu_read_lock();
1950         sma = sem_obtain_lock(ns, semid, sops, nsops, &locknum);
1951 
1952         /*
1953          * Wait until it's guaranteed that no wakeup_sem_queue_do() is ongoing.
1954          */
1955         error = get_queue_result(&queue);
1956 
1957         /*
1958          * Array removed? If yes, leave without sem_unlock().
1959          */
1960         if (IS_ERR(sma)) {
1961                 rcu_read_unlock();
1962                 goto out_free;
1963         }
1964 
1965 
1966         /*
1967          * If queue.status != -EINTR we are woken up by another process.
1968          * Leave without unlink_queue(), but with sem_unlock().
1969          */
1970         if (error != -EINTR)
1971                 goto out_unlock_free;
1972 
1973         /*
1974          * If an interrupt occurred we have to clean up the queue
1975          */
1976         if (timeout && jiffies_left == 0)
1977                 error = -EAGAIN;
1978 
1979         /*
1980          * If the wakeup was spurious, just retry
1981          */
1982         if (error == -EINTR && !signal_pending(current))
1983                 goto sleep_again;
1984 
1985         unlink_queue(sma, &queue);
1986 
1987 out_unlock_free:
1988         sem_unlock(sma, locknum);
1989 out_rcu_wakeup:
1990         rcu_read_unlock();
1991         wake_up_sem_queue_do(&tasks);
1992 out_free:
1993         if (sops != fast_sops)
1994                 kfree(sops);
1995         return error;
1996 }
1997 
1998 SYSCALL_DEFINE3(semop, int, semid, struct sembuf __user *, tsops,
1999                 unsigned, nsops)
2000 {
2001         return sys_semtimedop(semid, tsops, nsops, NULL);
2002 }
2003 
2004 /* If CLONE_SYSVSEM is set, establish sharing of SEM_UNDO state between
2005  * parent and child tasks.
2006  */
2007 
2008 int copy_semundo(unsigned long clone_flags, struct task_struct *tsk)
2009 {
2010         struct sem_undo_list *undo_list;
2011         int error;
2012 
2013         if (clone_flags & CLONE_SYSVSEM) {
2014                 error = get_undo_list(&undo_list);
2015                 if (error)
2016                         return error;
2017                 atomic_inc(&undo_list->refcnt);
2018                 tsk->sysvsem.undo_list = undo_list;
2019         } else 
2020                 tsk->sysvsem.undo_list = NULL;
2021 
2022         return 0;
2023 }
2024 
2025 /*
2026  * add semadj values to semaphores, free undo structures.
2027  * undo structures are not freed when semaphore arrays are destroyed
2028  * so some of them may be out of date.
2029  * IMPLEMENTATION NOTE: There is some confusion over whether the
2030  * set of adjustments that needs to be done should be done in an atomic
2031  * manner or not. That is, if we are attempting to decrement the semval
2032  * should we queue up and wait until we can do so legally?
2033  * The original implementation attempted to do this (queue and wait).
2034  * The current implementation does not do so. The POSIX standard
2035  * and SVID should be consulted to determine what behavior is mandated.
2036  */
2037 void exit_sem(struct task_struct *tsk)
2038 {
2039         struct sem_undo_list *ulp;
2040 
2041         ulp = tsk->sysvsem.undo_list;
2042         if (!ulp)
2043                 return;
2044         tsk->sysvsem.undo_list = NULL;
2045 
2046         if (!atomic_dec_and_test(&ulp->refcnt))
2047                 return;
2048 
2049         for (;;) {
2050                 struct sem_array *sma;
2051                 struct sem_undo *un;
2052                 struct list_head tasks;
2053                 int semid, i;
2054 
2055                 rcu_read_lock();
2056                 un = list_entry_rcu(ulp->list_proc.next,
2057                                     struct sem_undo, list_proc);
2058                 if (&un->list_proc == &ulp->list_proc)
2059                         semid = -1;
2060                  else
2061                         semid = un->semid;
2062 
2063                 if (semid == -1) {
2064                         rcu_read_unlock();
2065                         break;
2066                 }
2067 
2068                 sma = sem_obtain_object_check(tsk->nsproxy->ipc_ns, un->semid);
2069                 /* exit_sem raced with IPC_RMID, nothing to do */
2070                 if (IS_ERR(sma)) {
2071                         rcu_read_unlock();
2072                         continue;
2073                 }
2074 
2075                 sem_lock(sma, NULL, -1);
2076                 /* exit_sem raced with IPC_RMID, nothing to do */
2077                 if (!ipc_valid_object(&sma->sem_perm)) {
2078                         sem_unlock(sma, -1);
2079                         rcu_read_unlock();
2080                         continue;
2081                 }
2082                 un = __lookup_undo(ulp, semid);
2083                 if (un == NULL) {
2084                         /* exit_sem raced with IPC_RMID+semget() that created
2085                          * exactly the same semid. Nothing to do.
2086                          */
2087                         sem_unlock(sma, -1);
2088                         rcu_read_unlock();
2089                         continue;
2090                 }
2091 
2092                 /* remove un from the linked lists */
2093                 ipc_assert_locked_object(&sma->sem_perm);
2094                 list_del(&un->list_id);
2095 
2096                 spin_lock(&ulp->lock);
2097                 list_del_rcu(&un->list_proc);
2098                 spin_unlock(&ulp->lock);
2099 
2100                 /* perform adjustments registered in un */
2101                 for (i = 0; i < sma->sem_nsems; i++) {
2102                         struct sem *semaphore = &sma->sem_base[i];
2103                         if (un->semadj[i]) {
2104                                 semaphore->semval += un->semadj[i];
2105                                 /*
2106                                  * Range checks of the new semaphore value,
2107                                  * not defined by sus:
2108                                  * - Some unices ignore the undo entirely
2109                                  *   (e.g. HP UX 11i 11.22, Tru64 V5.1)
2110                                  * - some cap the value (e.g. FreeBSD caps
2111                                  *   at 0, but doesn't enforce SEMVMX)
2112                                  *
2113                                  * Linux caps the semaphore value, both at 0
2114                                  * and at SEMVMX.
2115                                  *
2116                                  *      Manfred <manfred@colorfullife.com>
2117                                  */
2118                                 if (semaphore->semval < 0)
2119                                         semaphore->semval = 0;
2120                                 if (semaphore->semval > SEMVMX)
2121                                         semaphore->semval = SEMVMX;
2122                                 semaphore->sempid = task_tgid_vnr(current);
2123                         }
2124                 }
2125                 /* maybe some queued-up processes were waiting for this */
2126                 INIT_LIST_HEAD(&tasks);
2127                 do_smart_update(sma, NULL, 0, 1, &tasks);
2128                 sem_unlock(sma, -1);
2129                 rcu_read_unlock();
2130                 wake_up_sem_queue_do(&tasks);
2131 
2132                 kfree_rcu(un, rcu);
2133         }
2134         kfree(ulp);
2135 }
2136 
2137 #ifdef CONFIG_PROC_FS
2138 static int sysvipc_sem_proc_show(struct seq_file *s, void *it)
2139 {
2140         struct user_namespace *user_ns = seq_user_ns(s);
2141         struct sem_array *sma = it;
2142         time_t sem_otime;
2143 
2144         /*
2145          * The proc interface isn't aware of sem_lock(), it calls
2146          * ipc_lock_object() directly (in sysvipc_find_ipc).
2147          * In order to stay compatible with sem_lock(), we must wait until
2148          * all simple semop() calls have left their critical regions.
2149          */
2150         sem_wait_array(sma);
2151 
2152         sem_otime = get_semotime(sma);
2153 
2154         return seq_printf(s,
2155                           "%10d %10d  %4o %10u %5u %5u %5u %5u %10lu %10lu\n",
2156                           sma->sem_perm.key,
2157                           sma->sem_perm.id,
2158                           sma->sem_perm.mode,
2159                           sma->sem_nsems,
2160                           from_kuid_munged(user_ns, sma->sem_perm.uid),
2161                           from_kgid_munged(user_ns, sma->sem_perm.gid),
2162                           from_kuid_munged(user_ns, sma->sem_perm.cuid),
2163                           from_kgid_munged(user_ns, sma->sem_perm.cgid),
2164                           sem_otime,
2165                           sma->sem_ctime);
2166 }
2167 #endif
2168 

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