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Linux/ipc/sem.c

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

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