3 * Copyright (C) 1992 Krishna Balasubramanian
4 * Copyright (C) 1995 Eric Schenk, Bruno Haible
6 * /proc/sysvipc/sem support (c) 1999 Dragos Acostachioaie <dragos@iname.com>
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
13 * (c) 2003 Manfred Spraul <manfred@colorfullife.com>
14 * (c) 2016 Davidlohr Bueso <dave@stgolabs.net>
15 * Further wakeup optimizations, documentation
16 * (c) 2010 Manfred Spraul <manfred@colorfullife.com>
18 * support for audit of ipc object properties and permission changes
19 * Dustin Kirkland <dustin.kirkland@us.ibm.com>
23 * Pavel Emelianov <xemul@openvz.org>
25 * Implementation notes: (May 2010)
26 * This file implements System V semaphores.
28 * User space visible behavior:
29 * - FIFO ordering for semop() operations (just FIFO, not starvation
31 * - multiple semaphore operations that alter the same semaphore in
32 * one semop() are handled.
33 * - sem_ctime (time of last semctl()) is updated in the IPC_SET, SETVAL and
35 * - two Linux specific semctl() commands: SEM_STAT, SEM_INFO.
36 * - undo adjustments at process exit are limited to 0..SEMVMX.
37 * - namespace are supported.
38 * - SEMMSL, SEMMNS, SEMOPM and SEMMNI can be configured at runtine by writing
39 * to /proc/sys/kernel/sem.
40 * - statistics about the usage are reported in /proc/sysvipc/sem.
44 * - all global variables are read-mostly.
45 * - semop() calls and semctl(RMID) are synchronized by RCU.
46 * - most operations do write operations (actually: spin_lock calls) to
47 * the per-semaphore array structure.
48 * Thus: Perfect SMP scaling between independent semaphore arrays.
49 * If multiple semaphores in one array are used, then cache line
50 * trashing on the semaphore array spinlock will limit the scaling.
51 * - semncnt and semzcnt are calculated on demand in count_semcnt()
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 * - 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 * - UNDO values are stored in an array (one per process and per
63 * semaphore array, lazily allocated). For backwards compatibility, multiple
64 * modes for the UNDO variables are supported (per process, per thread)
65 * (see copy_semundo, CLONE_SYSVSEM)
66 * - There are two lists of the pending operations: a per-array list
67 * and per-semaphore list (stored in the array). This allows to achieve FIFO
68 * ordering without always scanning all pending operations.
69 * The worst-case behavior is nevertheless O(N^2) for N wakeups.
72 #include <linux/slab.h>
73 #include <linux/spinlock.h>
74 #include <linux/init.h>
75 #include <linux/proc_fs.h>
76 #include <linux/time.h>
77 #include <linux/security.h>
78 #include <linux/syscalls.h>
79 #include <linux/audit.h>
80 #include <linux/capability.h>
81 #include <linux/seq_file.h>
82 #include <linux/rwsem.h>
83 #include <linux/nsproxy.h>
84 #include <linux/ipc_namespace.h>
86 #include <linux/uaccess.h>
89 /* One semaphore structure for each semaphore in the system. */
91 int semval; /* current value */
93 * PID of the process that last modified the semaphore. For
94 * Linux, specifically these are:
96 * - semctl, via SETVAL and SETALL.
97 * - at task exit when performing undo adjustments (see exit_sem).
100 spinlock_t lock; /* spinlock for fine-grained semtimedop */
101 struct list_head pending_alter; /* pending single-sop operations */
102 /* that alter the semaphore */
103 struct list_head pending_const; /* pending single-sop operations */
104 /* that do not alter the semaphore*/
105 time_t sem_otime; /* candidate for sem_otime */
106 } ____cacheline_aligned_in_smp;
108 /* One queue for each sleeping process in the system. */
110 struct list_head list; /* queue of pending operations */
111 struct task_struct *sleeper; /* this process */
112 struct sem_undo *undo; /* undo structure */
113 int pid; /* process id of requesting process */
114 int status; /* completion status of operation */
115 struct sembuf *sops; /* array of pending operations */
116 struct sembuf *blocking; /* the operation that blocked */
117 int nsops; /* number of operations */
118 bool alter; /* does *sops alter the array? */
119 bool dupsop; /* sops on more than one sem_num */
122 /* Each task has a list of undo requests. They are executed automatically
123 * when the process exits.
126 struct list_head list_proc; /* per-process list: *
127 * all undos from one process
129 struct rcu_head rcu; /* rcu struct for sem_undo */
130 struct sem_undo_list *ulp; /* back ptr to sem_undo_list */
131 struct list_head list_id; /* per semaphore array list:
132 * all undos for one array */
133 int semid; /* semaphore set identifier */
134 short *semadj; /* array of adjustments */
135 /* one per semaphore */
138 /* sem_undo_list controls shared access to the list of sem_undo structures
139 * that may be shared among all a CLONE_SYSVSEM task group.
141 struct sem_undo_list {
144 struct list_head list_proc;
148 #define sem_ids(ns) ((ns)->ids[IPC_SEM_IDS])
150 #define sem_checkid(sma, semid) ipc_checkid(&sma->sem_perm, semid)
152 static int newary(struct ipc_namespace *, struct ipc_params *);
153 static void freeary(struct ipc_namespace *, struct kern_ipc_perm *);
154 #ifdef CONFIG_PROC_FS
155 static int sysvipc_sem_proc_show(struct seq_file *s, void *it);
158 #define SEMMSL_FAST 256 /* 512 bytes on stack */
159 #define SEMOPM_FAST 64 /* ~ 372 bytes on stack */
162 * Switching from the mode suitable for simple ops
163 * to the mode for complex ops is costly. Therefore:
164 * use some hysteresis
166 #define USE_GLOBAL_LOCK_HYSTERESIS 10
170 * a) global sem_lock() for read/write
172 * sem_array.complex_count,
173 * sem_array.pending{_alter,_const},
176 * b) global or semaphore sem_lock() for read/write:
177 * sem_array.sem_base[i].pending_{const,alter}:
180 * sem_undo_list.list_proc:
181 * * undo_list->lock for write
184 * * global sem_lock() for write
185 * * either local or global sem_lock() for read.
188 * Most ordering is enforced by using spin_lock() and spin_unlock().
189 * The special case is use_global_lock:
190 * Setting it from non-zero to 0 is a RELEASE, this is ensured by
191 * using smp_store_release().
192 * Testing if it is non-zero is an ACQUIRE, this is ensured by using
193 * smp_load_acquire().
194 * Setting it from 0 to non-zero must be ordered with regards to
195 * this smp_load_acquire(), this is guaranteed because the smp_load_acquire()
196 * is inside a spin_lock() and after a write from 0 to non-zero a
197 * spin_lock()+spin_unlock() is done.
200 #define sc_semmsl sem_ctls[0]
201 #define sc_semmns sem_ctls[1]
202 #define sc_semopm sem_ctls[2]
203 #define sc_semmni sem_ctls[3]
205 void sem_init_ns(struct ipc_namespace *ns)
207 ns->sc_semmsl = SEMMSL;
208 ns->sc_semmns = SEMMNS;
209 ns->sc_semopm = SEMOPM;
210 ns->sc_semmni = SEMMNI;
212 ipc_init_ids(&ns->ids[IPC_SEM_IDS]);
216 void sem_exit_ns(struct ipc_namespace *ns)
218 free_ipcs(ns, &sem_ids(ns), freeary);
219 idr_destroy(&ns->ids[IPC_SEM_IDS].ipcs_idr);
223 void __init sem_init(void)
225 sem_init_ns(&init_ipc_ns);
226 ipc_init_proc_interface("sysvipc/sem",
227 " key semid perms nsems uid gid cuid cgid otime ctime\n",
228 IPC_SEM_IDS, sysvipc_sem_proc_show);
232 * unmerge_queues - unmerge queues, if possible.
233 * @sma: semaphore array
235 * The function unmerges the wait queues if complex_count is 0.
236 * It must be called prior to dropping the global semaphore array lock.
238 static void unmerge_queues(struct sem_array *sma)
240 struct sem_queue *q, *tq;
242 /* complex operations still around? */
243 if (sma->complex_count)
246 * We will switch back to simple mode.
247 * Move all pending operation back into the per-semaphore
250 list_for_each_entry_safe(q, tq, &sma->pending_alter, list) {
252 curr = &sma->sem_base[q->sops[0].sem_num];
254 list_add_tail(&q->list, &curr->pending_alter);
256 INIT_LIST_HEAD(&sma->pending_alter);
260 * merge_queues - merge single semop queues into global queue
261 * @sma: semaphore array
263 * This function merges all per-semaphore queues into the global queue.
264 * It is necessary to achieve FIFO ordering for the pending single-sop
265 * operations when a multi-semop operation must sleep.
266 * Only the alter operations must be moved, the const operations can stay.
268 static void merge_queues(struct sem_array *sma)
271 for (i = 0; i < sma->sem_nsems; i++) {
272 struct sem *sem = sma->sem_base + i;
274 list_splice_init(&sem->pending_alter, &sma->pending_alter);
278 static void sem_rcu_free(struct rcu_head *head)
280 struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu);
281 struct sem_array *sma = ipc_rcu_to_struct(p);
283 security_sem_free(sma);
288 * Enter the mode suitable for non-simple operations:
289 * Caller must own sem_perm.lock.
291 static void complexmode_enter(struct sem_array *sma)
296 if (sma->use_global_lock > 0) {
298 * We are already in global lock mode.
299 * Nothing to do, just reset the
300 * counter until we return to simple mode.
302 sma->use_global_lock = USE_GLOBAL_LOCK_HYSTERESIS;
305 sma->use_global_lock = USE_GLOBAL_LOCK_HYSTERESIS;
307 for (i = 0; i < sma->sem_nsems; i++) {
308 sem = sma->sem_base + i;
309 spin_lock(&sem->lock);
310 spin_unlock(&sem->lock);
315 * Try to leave the mode that disallows simple operations:
316 * Caller must own sem_perm.lock.
318 static void complexmode_tryleave(struct sem_array *sma)
320 if (sma->complex_count) {
321 /* Complex ops are sleeping.
322 * We must stay in complex mode
326 if (sma->use_global_lock == 1) {
328 * Immediately after setting use_global_lock to 0,
329 * a simple op can start. Thus: all memory writes
330 * performed by the current operation must be visible
331 * before we set use_global_lock to 0.
333 smp_store_release(&sma->use_global_lock, 0);
335 sma->use_global_lock--;
339 #define SEM_GLOBAL_LOCK (-1)
341 * If the request contains only one semaphore operation, and there are
342 * no complex transactions pending, lock only the semaphore involved.
343 * Otherwise, lock the entire semaphore array, since we either have
344 * multiple semaphores in our own semops, or we need to look at
345 * semaphores from other pending complex operations.
347 static inline int sem_lock(struct sem_array *sma, struct sembuf *sops,
353 /* Complex operation - acquire a full lock */
354 ipc_lock_object(&sma->sem_perm);
356 /* Prevent parallel simple ops */
357 complexmode_enter(sma);
358 return SEM_GLOBAL_LOCK;
362 * Only one semaphore affected - try to optimize locking.
363 * Optimized locking is possible if no complex operation
364 * is either enqueued or processed right now.
366 * Both facts are tracked by use_global_mode.
368 sem = sma->sem_base + sops->sem_num;
371 * Initial check for use_global_lock. Just an optimization,
372 * no locking, no memory barrier.
374 if (!sma->use_global_lock) {
376 * It appears that no complex operation is around.
377 * Acquire the per-semaphore lock.
379 spin_lock(&sem->lock);
381 /* pairs with smp_store_release() */
382 if (!smp_load_acquire(&sma->use_global_lock)) {
383 /* fast path successful! */
384 return sops->sem_num;
386 spin_unlock(&sem->lock);
389 /* slow path: acquire the full lock */
390 ipc_lock_object(&sma->sem_perm);
392 if (sma->use_global_lock == 0) {
394 * The use_global_lock mode ended while we waited for
395 * sma->sem_perm.lock. Thus we must switch to locking
397 * Unlike in the fast path, there is no need to recheck
398 * sma->use_global_lock after we have acquired sem->lock:
399 * We own sma->sem_perm.lock, thus use_global_lock cannot
402 spin_lock(&sem->lock);
404 ipc_unlock_object(&sma->sem_perm);
405 return sops->sem_num;
408 * Not a false alarm, thus continue to use the global lock
409 * mode. No need for complexmode_enter(), this was done by
410 * the caller that has set use_global_mode to non-zero.
412 return SEM_GLOBAL_LOCK;
416 static inline void sem_unlock(struct sem_array *sma, int locknum)
418 if (locknum == SEM_GLOBAL_LOCK) {
420 complexmode_tryleave(sma);
421 ipc_unlock_object(&sma->sem_perm);
423 struct sem *sem = sma->sem_base + locknum;
424 spin_unlock(&sem->lock);
429 * sem_lock_(check_) routines are called in the paths where the rwsem
432 * The caller holds the RCU read lock.
434 static inline struct sem_array *sem_obtain_object(struct ipc_namespace *ns, int id)
436 struct kern_ipc_perm *ipcp = ipc_obtain_object_idr(&sem_ids(ns), id);
439 return ERR_CAST(ipcp);
441 return container_of(ipcp, struct sem_array, sem_perm);
444 static inline struct sem_array *sem_obtain_object_check(struct ipc_namespace *ns,
447 struct kern_ipc_perm *ipcp = ipc_obtain_object_check(&sem_ids(ns), id);
450 return ERR_CAST(ipcp);
452 return container_of(ipcp, struct sem_array, sem_perm);
455 static inline void sem_lock_and_putref(struct sem_array *sma)
457 sem_lock(sma, NULL, -1);
458 ipc_rcu_putref(sma, sem_rcu_free);
461 static inline void sem_rmid(struct ipc_namespace *ns, struct sem_array *s)
463 ipc_rmid(&sem_ids(ns), &s->sem_perm);
467 * newary - Create a new semaphore set
469 * @params: ptr to the structure that contains key, semflg and nsems
471 * Called with sem_ids.rwsem held (as a writer)
473 static int newary(struct ipc_namespace *ns, struct ipc_params *params)
477 struct sem_array *sma;
479 key_t key = params->key;
480 int nsems = params->u.nsems;
481 int semflg = params->flg;
486 if (ns->used_sems + nsems > ns->sc_semmns)
489 size = sizeof(*sma) + nsems * sizeof(struct sem);
490 sma = ipc_rcu_alloc(size);
494 memset(sma, 0, size);
496 sma->sem_perm.mode = (semflg & S_IRWXUGO);
497 sma->sem_perm.key = key;
499 sma->sem_perm.security = NULL;
500 retval = security_sem_alloc(sma);
502 ipc_rcu_putref(sma, ipc_rcu_free);
506 sma->sem_base = (struct sem *) &sma[1];
508 for (i = 0; i < nsems; i++) {
509 INIT_LIST_HEAD(&sma->sem_base[i].pending_alter);
510 INIT_LIST_HEAD(&sma->sem_base[i].pending_const);
511 spin_lock_init(&sma->sem_base[i].lock);
514 sma->complex_count = 0;
515 sma->use_global_lock = USE_GLOBAL_LOCK_HYSTERESIS;
516 INIT_LIST_HEAD(&sma->pending_alter);
517 INIT_LIST_HEAD(&sma->pending_const);
518 INIT_LIST_HEAD(&sma->list_id);
519 sma->sem_nsems = nsems;
520 sma->sem_ctime = get_seconds();
522 id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni);
524 ipc_rcu_putref(sma, sem_rcu_free);
527 ns->used_sems += nsems;
532 return sma->sem_perm.id;
537 * Called with sem_ids.rwsem and ipcp locked.
539 static inline int sem_security(struct kern_ipc_perm *ipcp, int semflg)
541 struct sem_array *sma;
543 sma = container_of(ipcp, struct sem_array, sem_perm);
544 return security_sem_associate(sma, semflg);
548 * Called with sem_ids.rwsem and ipcp locked.
550 static inline int sem_more_checks(struct kern_ipc_perm *ipcp,
551 struct ipc_params *params)
553 struct sem_array *sma;
555 sma = container_of(ipcp, struct sem_array, sem_perm);
556 if (params->u.nsems > sma->sem_nsems)
562 SYSCALL_DEFINE3(semget, key_t, key, int, nsems, int, semflg)
564 struct ipc_namespace *ns;
565 static const struct ipc_ops sem_ops = {
567 .associate = sem_security,
568 .more_checks = sem_more_checks,
570 struct ipc_params sem_params;
572 ns = current->nsproxy->ipc_ns;
574 if (nsems < 0 || nsems > ns->sc_semmsl)
577 sem_params.key = key;
578 sem_params.flg = semflg;
579 sem_params.u.nsems = nsems;
581 return ipcget(ns, &sem_ids(ns), &sem_ops, &sem_params);
585 * perform_atomic_semop[_slow] - Attempt to perform semaphore
586 * operations on a given array.
587 * @sma: semaphore array
588 * @q: struct sem_queue that describes the operation
590 * Caller blocking are as follows, based the value
591 * indicated by the semaphore operation (sem_op):
593 * (1) >0 never blocks.
594 * (2) 0 (wait-for-zero operation): semval is non-zero.
595 * (3) <0 attempting to decrement semval to a value smaller than zero.
597 * Returns 0 if the operation was possible.
598 * Returns 1 if the operation is impossible, the caller must sleep.
599 * Returns <0 for error codes.
601 static int perform_atomic_semop_slow(struct sem_array *sma, struct sem_queue *q)
603 int result, sem_op, nsops, pid;
613 for (sop = sops; sop < sops + nsops; sop++) {
614 curr = sma->sem_base + sop->sem_num;
615 sem_op = sop->sem_op;
616 result = curr->semval;
618 if (!sem_op && result)
627 if (sop->sem_flg & SEM_UNDO) {
628 int undo = un->semadj[sop->sem_num] - sem_op;
629 /* Exceeding the undo range is an error. */
630 if (undo < (-SEMAEM - 1) || undo > SEMAEM)
632 un->semadj[sop->sem_num] = undo;
635 curr->semval = result;
640 while (sop >= sops) {
641 sma->sem_base[sop->sem_num].sempid = pid;
654 if (sop->sem_flg & IPC_NOWAIT)
661 while (sop >= sops) {
662 sem_op = sop->sem_op;
663 sma->sem_base[sop->sem_num].semval -= sem_op;
664 if (sop->sem_flg & SEM_UNDO)
665 un->semadj[sop->sem_num] += sem_op;
672 static int perform_atomic_semop(struct sem_array *sma, struct sem_queue *q)
674 int result, sem_op, nsops;
684 if (unlikely(q->dupsop))
685 return perform_atomic_semop_slow(sma, q);
688 * We scan the semaphore set twice, first to ensure that the entire
689 * operation can succeed, therefore avoiding any pointless writes
690 * to shared memory and having to undo such changes in order to block
691 * until the operations can go through.
693 for (sop = sops; sop < sops + nsops; sop++) {
694 curr = sma->sem_base + sop->sem_num;
695 sem_op = sop->sem_op;
696 result = curr->semval;
698 if (!sem_op && result)
699 goto would_block; /* wait-for-zero */
708 if (sop->sem_flg & SEM_UNDO) {
709 int undo = un->semadj[sop->sem_num] - sem_op;
711 /* Exceeding the undo range is an error. */
712 if (undo < (-SEMAEM - 1) || undo > SEMAEM)
717 for (sop = sops; sop < sops + nsops; sop++) {
718 curr = sma->sem_base + sop->sem_num;
719 sem_op = sop->sem_op;
720 result = curr->semval;
722 if (sop->sem_flg & SEM_UNDO) {
723 int undo = un->semadj[sop->sem_num] - sem_op;
725 un->semadj[sop->sem_num] = undo;
727 curr->semval += sem_op;
728 curr->sempid = q->pid;
735 return sop->sem_flg & IPC_NOWAIT ? -EAGAIN : 1;
738 static inline void wake_up_sem_queue_prepare(struct sem_queue *q, int error,
739 struct wake_q_head *wake_q)
741 wake_q_add(wake_q, q->sleeper);
743 * Rely on the above implicit barrier, such that we can
744 * ensure that we hold reference to the task before setting
745 * q->status. Otherwise we could race with do_exit if the
746 * task is awoken by an external event before calling
749 WRITE_ONCE(q->status, error);
752 static void unlink_queue(struct sem_array *sma, struct sem_queue *q)
756 sma->complex_count--;
759 /** check_restart(sma, q)
760 * @sma: semaphore array
761 * @q: the operation that just completed
763 * update_queue is O(N^2) when it restarts scanning the whole queue of
764 * waiting operations. Therefore this function checks if the restart is
765 * really necessary. It is called after a previously waiting operation
766 * modified the array.
767 * Note that wait-for-zero operations are handled without restart.
769 static inline int check_restart(struct sem_array *sma, struct sem_queue *q)
771 /* pending complex alter operations are too difficult to analyse */
772 if (!list_empty(&sma->pending_alter))
775 /* we were a sleeping complex operation. Too difficult */
779 /* It is impossible that someone waits for the new value:
780 * - complex operations always restart.
781 * - wait-for-zero are handled seperately.
782 * - q is a previously sleeping simple operation that
783 * altered the array. It must be a decrement, because
784 * simple increments never sleep.
785 * - If there are older (higher priority) decrements
786 * in the queue, then they have observed the original
787 * semval value and couldn't proceed. The operation
788 * decremented to value - thus they won't proceed either.
794 * wake_const_ops - wake up non-alter tasks
795 * @sma: semaphore array.
796 * @semnum: semaphore that was modified.
797 * @wake_q: lockless wake-queue head.
799 * wake_const_ops must be called after a semaphore in a semaphore array
800 * was set to 0. If complex const operations are pending, wake_const_ops must
801 * be called with semnum = -1, as well as with the number of each modified
803 * The tasks that must be woken up are added to @wake_q. The return code
804 * is stored in q->pid.
805 * The function returns 1 if at least one operation was completed successfully.
807 static int wake_const_ops(struct sem_array *sma, int semnum,
808 struct wake_q_head *wake_q)
810 struct sem_queue *q, *tmp;
811 struct list_head *pending_list;
812 int semop_completed = 0;
815 pending_list = &sma->pending_const;
817 pending_list = &sma->sem_base[semnum].pending_const;
819 list_for_each_entry_safe(q, tmp, pending_list, list) {
820 int error = perform_atomic_semop(sma, q);
824 /* operation completed, remove from queue & wakeup */
825 unlink_queue(sma, q);
827 wake_up_sem_queue_prepare(q, error, wake_q);
832 return semop_completed;
836 * do_smart_wakeup_zero - wakeup all wait for zero tasks
837 * @sma: semaphore array
838 * @sops: operations that were performed
839 * @nsops: number of operations
840 * @wake_q: lockless wake-queue head
842 * Checks all required queue for wait-for-zero operations, based
843 * on the actual changes that were performed on the semaphore array.
844 * The function returns 1 if at least one operation was completed successfully.
846 static int do_smart_wakeup_zero(struct sem_array *sma, struct sembuf *sops,
847 int nsops, struct wake_q_head *wake_q)
850 int semop_completed = 0;
853 /* first: the per-semaphore queues, if known */
855 for (i = 0; i < nsops; i++) {
856 int num = sops[i].sem_num;
858 if (sma->sem_base[num].semval == 0) {
860 semop_completed |= wake_const_ops(sma, num, wake_q);
865 * No sops means modified semaphores not known.
866 * Assume all were changed.
868 for (i = 0; i < sma->sem_nsems; i++) {
869 if (sma->sem_base[i].semval == 0) {
871 semop_completed |= wake_const_ops(sma, i, wake_q);
876 * If one of the modified semaphores got 0,
877 * then check the global queue, too.
880 semop_completed |= wake_const_ops(sma, -1, wake_q);
882 return semop_completed;
887 * update_queue - look for tasks that can be completed.
888 * @sma: semaphore array.
889 * @semnum: semaphore that was modified.
890 * @wake_q: lockless wake-queue head.
892 * update_queue must be called after a semaphore in a semaphore array
893 * was modified. If multiple semaphores were modified, update_queue must
894 * be called with semnum = -1, as well as with the number of each modified
896 * The tasks that must be woken up are added to @wake_q. The return code
897 * is stored in q->pid.
898 * The function internally checks if const operations can now succeed.
900 * The function return 1 if at least one semop was completed successfully.
902 static int update_queue(struct sem_array *sma, int semnum, struct wake_q_head *wake_q)
904 struct sem_queue *q, *tmp;
905 struct list_head *pending_list;
906 int semop_completed = 0;
909 pending_list = &sma->pending_alter;
911 pending_list = &sma->sem_base[semnum].pending_alter;
914 list_for_each_entry_safe(q, tmp, pending_list, list) {
917 /* If we are scanning the single sop, per-semaphore list of
918 * one semaphore and that semaphore is 0, then it is not
919 * necessary to scan further: simple increments
920 * that affect only one entry succeed immediately and cannot
921 * be in the per semaphore pending queue, and decrements
922 * cannot be successful if the value is already 0.
924 if (semnum != -1 && sma->sem_base[semnum].semval == 0)
927 error = perform_atomic_semop(sma, q);
929 /* Does q->sleeper still need to sleep? */
933 unlink_queue(sma, q);
939 do_smart_wakeup_zero(sma, q->sops, q->nsops, wake_q);
940 restart = check_restart(sma, q);
943 wake_up_sem_queue_prepare(q, error, wake_q);
947 return semop_completed;
951 * set_semotime - set sem_otime
952 * @sma: semaphore array
953 * @sops: operations that modified the array, may be NULL
955 * sem_otime is replicated to avoid cache line trashing.
956 * This function sets one instance to the current time.
958 static void set_semotime(struct sem_array *sma, struct sembuf *sops)
961 sma->sem_base[0].sem_otime = get_seconds();
963 sma->sem_base[sops[0].sem_num].sem_otime =
969 * do_smart_update - optimized update_queue
970 * @sma: semaphore array
971 * @sops: operations that were performed
972 * @nsops: number of operations
973 * @otime: force setting otime
974 * @wake_q: lockless wake-queue head
976 * do_smart_update() does the required calls to update_queue and wakeup_zero,
977 * based on the actual changes that were performed on the semaphore array.
978 * Note that the function does not do the actual wake-up: the caller is
979 * responsible for calling wake_up_q().
980 * It is safe to perform this call after dropping all locks.
982 static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsops,
983 int otime, struct wake_q_head *wake_q)
987 otime |= do_smart_wakeup_zero(sma, sops, nsops, wake_q);
989 if (!list_empty(&sma->pending_alter)) {
990 /* semaphore array uses the global queue - just process it. */
991 otime |= update_queue(sma, -1, wake_q);
995 * No sops, thus the modified semaphores are not
998 for (i = 0; i < sma->sem_nsems; i++)
999 otime |= update_queue(sma, i, wake_q);
1002 * Check the semaphores that were increased:
1003 * - No complex ops, thus all sleeping ops are
1005 * - if we decreased the value, then any sleeping
1006 * semaphore ops wont be able to run: If the
1007 * previous value was too small, then the new
1008 * value will be too small, too.
1010 for (i = 0; i < nsops; i++) {
1011 if (sops[i].sem_op > 0) {
1012 otime |= update_queue(sma,
1013 sops[i].sem_num, wake_q);
1019 set_semotime(sma, sops);
1023 * check_qop: Test if a queued operation sleeps on the semaphore semnum
1025 static int check_qop(struct sem_array *sma, int semnum, struct sem_queue *q,
1028 struct sembuf *sop = q->blocking;
1031 * Linux always (since 0.99.10) reported a task as sleeping on all
1032 * semaphores. This violates SUS, therefore it was changed to the
1033 * standard compliant behavior.
1034 * Give the administrators a chance to notice that an application
1035 * might misbehave because it relies on the Linux behavior.
1037 pr_info_once("semctl(GETNCNT/GETZCNT) is since 3.16 Single Unix Specification compliant.\n"
1038 "The task %s (%d) triggered the difference, watch for misbehavior.\n",
1039 current->comm, task_pid_nr(current));
1041 if (sop->sem_num != semnum)
1044 if (count_zero && sop->sem_op == 0)
1046 if (!count_zero && sop->sem_op < 0)
1052 /* The following counts are associated to each semaphore:
1053 * semncnt number of tasks waiting on semval being nonzero
1054 * semzcnt number of tasks waiting on semval being zero
1056 * Per definition, a task waits only on the semaphore of the first semop
1057 * that cannot proceed, even if additional operation would block, too.
1059 static int count_semcnt(struct sem_array *sma, ushort semnum,
1062 struct list_head *l;
1063 struct sem_queue *q;
1067 /* First: check the simple operations. They are easy to evaluate */
1069 l = &sma->sem_base[semnum].pending_const;
1071 l = &sma->sem_base[semnum].pending_alter;
1073 list_for_each_entry(q, l, list) {
1074 /* all task on a per-semaphore list sleep on exactly
1080 /* Then: check the complex operations. */
1081 list_for_each_entry(q, &sma->pending_alter, list) {
1082 semcnt += check_qop(sma, semnum, q, count_zero);
1085 list_for_each_entry(q, &sma->pending_const, list) {
1086 semcnt += check_qop(sma, semnum, q, count_zero);
1092 /* Free a semaphore set. freeary() is called with sem_ids.rwsem locked
1093 * as a writer and the spinlock for this semaphore set hold. sem_ids.rwsem
1094 * remains locked on exit.
1096 static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
1098 struct sem_undo *un, *tu;
1099 struct sem_queue *q, *tq;
1100 struct sem_array *sma = container_of(ipcp, struct sem_array, sem_perm);
1102 DEFINE_WAKE_Q(wake_q);
1104 /* Free the existing undo structures for this semaphore set. */
1105 ipc_assert_locked_object(&sma->sem_perm);
1106 list_for_each_entry_safe(un, tu, &sma->list_id, list_id) {
1107 list_del(&un->list_id);
1108 spin_lock(&un->ulp->lock);
1110 list_del_rcu(&un->list_proc);
1111 spin_unlock(&un->ulp->lock);
1115 /* Wake up all pending processes and let them fail with EIDRM. */
1116 list_for_each_entry_safe(q, tq, &sma->pending_const, list) {
1117 unlink_queue(sma, q);
1118 wake_up_sem_queue_prepare(q, -EIDRM, &wake_q);
1121 list_for_each_entry_safe(q, tq, &sma->pending_alter, list) {
1122 unlink_queue(sma, q);
1123 wake_up_sem_queue_prepare(q, -EIDRM, &wake_q);
1125 for (i = 0; i < sma->sem_nsems; i++) {
1126 struct sem *sem = sma->sem_base + i;
1127 list_for_each_entry_safe(q, tq, &sem->pending_const, list) {
1128 unlink_queue(sma, q);
1129 wake_up_sem_queue_prepare(q, -EIDRM, &wake_q);
1131 list_for_each_entry_safe(q, tq, &sem->pending_alter, list) {
1132 unlink_queue(sma, q);
1133 wake_up_sem_queue_prepare(q, -EIDRM, &wake_q);
1137 /* Remove the semaphore set from the IDR */
1139 sem_unlock(sma, -1);
1143 ns->used_sems -= sma->sem_nsems;
1144 ipc_rcu_putref(sma, sem_rcu_free);
1147 static unsigned long copy_semid_to_user(void __user *buf, struct semid64_ds *in, int version)
1151 return copy_to_user(buf, in, sizeof(*in));
1154 struct semid_ds out;
1156 memset(&out, 0, sizeof(out));
1158 ipc64_perm_to_ipc_perm(&in->sem_perm, &out.sem_perm);
1160 out.sem_otime = in->sem_otime;
1161 out.sem_ctime = in->sem_ctime;
1162 out.sem_nsems = in->sem_nsems;
1164 return copy_to_user(buf, &out, sizeof(out));
1171 static time_t get_semotime(struct sem_array *sma)
1176 res = sma->sem_base[0].sem_otime;
1177 for (i = 1; i < sma->sem_nsems; i++) {
1178 time_t to = sma->sem_base[i].sem_otime;
1186 static int semctl_nolock(struct ipc_namespace *ns, int semid,
1187 int cmd, int version, void __user *p)
1190 struct sem_array *sma;
1196 struct seminfo seminfo;
1199 err = security_sem_semctl(NULL, cmd);
1203 memset(&seminfo, 0, sizeof(seminfo));
1204 seminfo.semmni = ns->sc_semmni;
1205 seminfo.semmns = ns->sc_semmns;
1206 seminfo.semmsl = ns->sc_semmsl;
1207 seminfo.semopm = ns->sc_semopm;
1208 seminfo.semvmx = SEMVMX;
1209 seminfo.semmnu = SEMMNU;
1210 seminfo.semmap = SEMMAP;
1211 seminfo.semume = SEMUME;
1212 down_read(&sem_ids(ns).rwsem);
1213 if (cmd == SEM_INFO) {
1214 seminfo.semusz = sem_ids(ns).in_use;
1215 seminfo.semaem = ns->used_sems;
1217 seminfo.semusz = SEMUSZ;
1218 seminfo.semaem = SEMAEM;
1220 max_id = ipc_get_maxid(&sem_ids(ns));
1221 up_read(&sem_ids(ns).rwsem);
1222 if (copy_to_user(p, &seminfo, sizeof(struct seminfo)))
1224 return (max_id < 0) ? 0 : max_id;
1229 struct semid64_ds tbuf;
1232 memset(&tbuf, 0, sizeof(tbuf));
1235 if (cmd == SEM_STAT) {
1236 sma = sem_obtain_object(ns, semid);
1241 id = sma->sem_perm.id;
1243 sma = sem_obtain_object_check(ns, semid);
1251 if (ipcperms(ns, &sma->sem_perm, S_IRUGO))
1254 err = security_sem_semctl(sma, cmd);
1258 kernel_to_ipc64_perm(&sma->sem_perm, &tbuf.sem_perm);
1259 tbuf.sem_otime = get_semotime(sma);
1260 tbuf.sem_ctime = sma->sem_ctime;
1261 tbuf.sem_nsems = sma->sem_nsems;
1263 if (copy_semid_to_user(p, &tbuf, version))
1275 static int semctl_setval(struct ipc_namespace *ns, int semid, int semnum,
1278 struct sem_undo *un;
1279 struct sem_array *sma;
1282 DEFINE_WAKE_Q(wake_q);
1284 #if defined(CONFIG_64BIT) && defined(__BIG_ENDIAN)
1285 /* big-endian 64bit */
1288 /* 32bit or little-endian 64bit */
1292 if (val > SEMVMX || val < 0)
1296 sma = sem_obtain_object_check(ns, semid);
1299 return PTR_ERR(sma);
1302 if (semnum < 0 || semnum >= sma->sem_nsems) {
1308 if (ipcperms(ns, &sma->sem_perm, S_IWUGO)) {
1313 err = security_sem_semctl(sma, SETVAL);
1319 sem_lock(sma, NULL, -1);
1321 if (!ipc_valid_object(&sma->sem_perm)) {
1322 sem_unlock(sma, -1);
1327 curr = &sma->sem_base[semnum];
1329 ipc_assert_locked_object(&sma->sem_perm);
1330 list_for_each_entry(un, &sma->list_id, list_id)
1331 un->semadj[semnum] = 0;
1334 curr->sempid = task_tgid_vnr(current);
1335 sma->sem_ctime = get_seconds();
1336 /* maybe some queued-up processes were waiting for this */
1337 do_smart_update(sma, NULL, 0, 0, &wake_q);
1338 sem_unlock(sma, -1);
1344 static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
1345 int cmd, void __user *p)
1347 struct sem_array *sma;
1350 ushort fast_sem_io[SEMMSL_FAST];
1351 ushort *sem_io = fast_sem_io;
1352 DEFINE_WAKE_Q(wake_q);
1355 sma = sem_obtain_object_check(ns, semid);
1358 return PTR_ERR(sma);
1361 nsems = sma->sem_nsems;
1364 if (ipcperms(ns, &sma->sem_perm, cmd == SETALL ? S_IWUGO : S_IRUGO))
1365 goto out_rcu_wakeup;
1367 err = security_sem_semctl(sma, cmd);
1369 goto out_rcu_wakeup;
1375 ushort __user *array = p;
1378 sem_lock(sma, NULL, -1);
1379 if (!ipc_valid_object(&sma->sem_perm)) {
1383 if (nsems > SEMMSL_FAST) {
1384 if (!ipc_rcu_getref(sma)) {
1388 sem_unlock(sma, -1);
1390 sem_io = ipc_alloc(sizeof(ushort)*nsems);
1391 if (sem_io == NULL) {
1392 ipc_rcu_putref(sma, sem_rcu_free);
1397 sem_lock_and_putref(sma);
1398 if (!ipc_valid_object(&sma->sem_perm)) {
1403 for (i = 0; i < sma->sem_nsems; i++)
1404 sem_io[i] = sma->sem_base[i].semval;
1405 sem_unlock(sma, -1);
1408 if (copy_to_user(array, sem_io, nsems*sizeof(ushort)))
1415 struct sem_undo *un;
1417 if (!ipc_rcu_getref(sma)) {
1419 goto out_rcu_wakeup;
1423 if (nsems > SEMMSL_FAST) {
1424 sem_io = ipc_alloc(sizeof(ushort)*nsems);
1425 if (sem_io == NULL) {
1426 ipc_rcu_putref(sma, sem_rcu_free);
1431 if (copy_from_user(sem_io, p, nsems*sizeof(ushort))) {
1432 ipc_rcu_putref(sma, sem_rcu_free);
1437 for (i = 0; i < nsems; i++) {
1438 if (sem_io[i] > SEMVMX) {
1439 ipc_rcu_putref(sma, sem_rcu_free);
1445 sem_lock_and_putref(sma);
1446 if (!ipc_valid_object(&sma->sem_perm)) {
1451 for (i = 0; i < nsems; i++) {
1452 sma->sem_base[i].semval = sem_io[i];
1453 sma->sem_base[i].sempid = task_tgid_vnr(current);
1456 ipc_assert_locked_object(&sma->sem_perm);
1457 list_for_each_entry(un, &sma->list_id, list_id) {
1458 for (i = 0; i < nsems; i++)
1461 sma->sem_ctime = get_seconds();
1462 /* maybe some queued-up processes were waiting for this */
1463 do_smart_update(sma, NULL, 0, 0, &wake_q);
1467 /* GETVAL, GETPID, GETNCTN, GETZCNT: fall-through */
1470 if (semnum < 0 || semnum >= nsems)
1471 goto out_rcu_wakeup;
1473 sem_lock(sma, NULL, -1);
1474 if (!ipc_valid_object(&sma->sem_perm)) {
1478 curr = &sma->sem_base[semnum];
1488 err = count_semcnt(sma, semnum, 0);
1491 err = count_semcnt(sma, semnum, 1);
1496 sem_unlock(sma, -1);
1501 if (sem_io != fast_sem_io)
1506 static inline unsigned long
1507 copy_semid_from_user(struct semid64_ds *out, void __user *buf, int version)
1511 if (copy_from_user(out, buf, sizeof(*out)))
1516 struct semid_ds tbuf_old;
1518 if (copy_from_user(&tbuf_old, buf, sizeof(tbuf_old)))
1521 out->sem_perm.uid = tbuf_old.sem_perm.uid;
1522 out->sem_perm.gid = tbuf_old.sem_perm.gid;
1523 out->sem_perm.mode = tbuf_old.sem_perm.mode;
1533 * This function handles some semctl commands which require the rwsem
1534 * to be held in write mode.
1535 * NOTE: no locks must be held, the rwsem is taken inside this function.
1537 static int semctl_down(struct ipc_namespace *ns, int semid,
1538 int cmd, int version, void __user *p)
1540 struct sem_array *sma;
1542 struct semid64_ds semid64;
1543 struct kern_ipc_perm *ipcp;
1545 if (cmd == IPC_SET) {
1546 if (copy_semid_from_user(&semid64, p, version))
1550 down_write(&sem_ids(ns).rwsem);
1553 ipcp = ipcctl_pre_down_nolock(ns, &sem_ids(ns), semid, cmd,
1554 &semid64.sem_perm, 0);
1556 err = PTR_ERR(ipcp);
1560 sma = container_of(ipcp, struct sem_array, sem_perm);
1562 err = security_sem_semctl(sma, cmd);
1568 sem_lock(sma, NULL, -1);
1569 /* freeary unlocks the ipc object and rcu */
1573 sem_lock(sma, NULL, -1);
1574 err = ipc_update_perm(&semid64.sem_perm, ipcp);
1577 sma->sem_ctime = get_seconds();
1585 sem_unlock(sma, -1);
1589 up_write(&sem_ids(ns).rwsem);
1593 SYSCALL_DEFINE4(semctl, int, semid, int, semnum, int, cmd, unsigned long, arg)
1596 struct ipc_namespace *ns;
1597 void __user *p = (void __user *)arg;
1602 version = ipc_parse_version(&cmd);
1603 ns = current->nsproxy->ipc_ns;
1610 return semctl_nolock(ns, semid, cmd, version, p);
1617 return semctl_main(ns, semid, semnum, cmd, p);
1619 return semctl_setval(ns, semid, semnum, arg);
1622 return semctl_down(ns, semid, cmd, version, p);
1628 /* If the task doesn't already have a undo_list, then allocate one
1629 * here. We guarantee there is only one thread using this undo list,
1630 * and current is THE ONE
1632 * If this allocation and assignment succeeds, but later
1633 * portions of this code fail, there is no need to free the sem_undo_list.
1634 * Just let it stay associated with the task, and it'll be freed later
1637 * This can block, so callers must hold no locks.
1639 static inline int get_undo_list(struct sem_undo_list **undo_listp)
1641 struct sem_undo_list *undo_list;
1643 undo_list = current->sysvsem.undo_list;
1645 undo_list = kzalloc(sizeof(*undo_list), GFP_KERNEL);
1646 if (undo_list == NULL)
1648 spin_lock_init(&undo_list->lock);
1649 atomic_set(&undo_list->refcnt, 1);
1650 INIT_LIST_HEAD(&undo_list->list_proc);
1652 current->sysvsem.undo_list = undo_list;
1654 *undo_listp = undo_list;
1658 static struct sem_undo *__lookup_undo(struct sem_undo_list *ulp, int semid)
1660 struct sem_undo *un;
1662 list_for_each_entry_rcu(un, &ulp->list_proc, list_proc) {
1663 if (un->semid == semid)
1669 static struct sem_undo *lookup_undo(struct sem_undo_list *ulp, int semid)
1671 struct sem_undo *un;
1673 assert_spin_locked(&ulp->lock);
1675 un = __lookup_undo(ulp, semid);
1677 list_del_rcu(&un->list_proc);
1678 list_add_rcu(&un->list_proc, &ulp->list_proc);
1684 * find_alloc_undo - lookup (and if not present create) undo array
1686 * @semid: semaphore array id
1688 * The function looks up (and if not present creates) the undo structure.
1689 * The size of the undo structure depends on the size of the semaphore
1690 * array, thus the alloc path is not that straightforward.
1691 * Lifetime-rules: sem_undo is rcu-protected, on success, the function
1692 * performs a rcu_read_lock().
1694 static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
1696 struct sem_array *sma;
1697 struct sem_undo_list *ulp;
1698 struct sem_undo *un, *new;
1701 error = get_undo_list(&ulp);
1703 return ERR_PTR(error);
1706 spin_lock(&ulp->lock);
1707 un = lookup_undo(ulp, semid);
1708 spin_unlock(&ulp->lock);
1709 if (likely(un != NULL))
1712 /* no undo structure around - allocate one. */
1713 /* step 1: figure out the size of the semaphore array */
1714 sma = sem_obtain_object_check(ns, semid);
1717 return ERR_CAST(sma);
1720 nsems = sma->sem_nsems;
1721 if (!ipc_rcu_getref(sma)) {
1723 un = ERR_PTR(-EIDRM);
1728 /* step 2: allocate new undo structure */
1729 new = kzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems, GFP_KERNEL);
1731 ipc_rcu_putref(sma, sem_rcu_free);
1732 return ERR_PTR(-ENOMEM);
1735 /* step 3: Acquire the lock on semaphore array */
1737 sem_lock_and_putref(sma);
1738 if (!ipc_valid_object(&sma->sem_perm)) {
1739 sem_unlock(sma, -1);
1742 un = ERR_PTR(-EIDRM);
1745 spin_lock(&ulp->lock);
1748 * step 4: check for races: did someone else allocate the undo struct?
1750 un = lookup_undo(ulp, semid);
1755 /* step 5: initialize & link new undo structure */
1756 new->semadj = (short *) &new[1];
1759 assert_spin_locked(&ulp->lock);
1760 list_add_rcu(&new->list_proc, &ulp->list_proc);
1761 ipc_assert_locked_object(&sma->sem_perm);
1762 list_add(&new->list_id, &sma->list_id);
1766 spin_unlock(&ulp->lock);
1767 sem_unlock(sma, -1);
1772 SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
1773 unsigned, nsops, const struct timespec __user *, timeout)
1775 int error = -EINVAL;
1776 struct sem_array *sma;
1777 struct sembuf fast_sops[SEMOPM_FAST];
1778 struct sembuf *sops = fast_sops, *sop;
1779 struct sem_undo *un;
1781 bool undos = false, alter = false, dupsop = false;
1782 struct sem_queue queue;
1783 unsigned long dup = 0, jiffies_left = 0;
1784 struct ipc_namespace *ns;
1786 ns = current->nsproxy->ipc_ns;
1788 if (nsops < 1 || semid < 0)
1790 if (nsops > ns->sc_semopm)
1792 if (nsops > SEMOPM_FAST) {
1793 sops = kmalloc(sizeof(*sops)*nsops, GFP_KERNEL);
1798 if (copy_from_user(sops, tsops, nsops * sizeof(*tsops))) {
1804 struct timespec _timeout;
1805 if (copy_from_user(&_timeout, timeout, sizeof(*timeout))) {
1809 if (_timeout.tv_sec < 0 || _timeout.tv_nsec < 0 ||
1810 _timeout.tv_nsec >= 1000000000L) {
1814 jiffies_left = timespec_to_jiffies(&_timeout);
1818 for (sop = sops; sop < sops + nsops; sop++) {
1819 unsigned long mask = 1ULL << ((sop->sem_num) % BITS_PER_LONG);
1821 if (sop->sem_num >= max)
1823 if (sop->sem_flg & SEM_UNDO)
1827 * There was a previous alter access that appears
1828 * to have accessed the same semaphore, thus use
1829 * the dupsop logic. "appears", because the detection
1830 * can only check % BITS_PER_LONG.
1834 if (sop->sem_op != 0) {
1841 /* On success, find_alloc_undo takes the rcu_read_lock */
1842 un = find_alloc_undo(ns, semid);
1844 error = PTR_ERR(un);
1852 sma = sem_obtain_object_check(ns, semid);
1855 error = PTR_ERR(sma);
1860 if (max >= sma->sem_nsems) {
1866 if (ipcperms(ns, &sma->sem_perm, alter ? S_IWUGO : S_IRUGO)) {
1871 error = security_sem_semop(sma, sops, nsops, alter);
1878 locknum = sem_lock(sma, sops, nsops);
1880 * We eventually might perform the following check in a lockless
1881 * fashion, considering ipc_valid_object() locking constraints.
1882 * If nsops == 1 and there is no contention for sem_perm.lock, then
1883 * only a per-semaphore lock is held and it's OK to proceed with the
1884 * check below. More details on the fine grained locking scheme
1885 * entangled here and why it's RMID race safe on comments at sem_lock()
1887 if (!ipc_valid_object(&sma->sem_perm))
1888 goto out_unlock_free;
1890 * semid identifiers are not unique - find_alloc_undo may have
1891 * allocated an undo structure, it was invalidated by an RMID
1892 * and now a new array with received the same id. Check and fail.
1893 * This case can be detected checking un->semid. The existence of
1894 * "un" itself is guaranteed by rcu.
1896 if (un && un->semid == -1)
1897 goto out_unlock_free;
1900 queue.nsops = nsops;
1902 queue.pid = task_tgid_vnr(current);
1903 queue.alter = alter;
1904 queue.dupsop = dupsop;
1906 error = perform_atomic_semop(sma, &queue);
1907 if (error == 0) { /* non-blocking succesfull path */
1908 DEFINE_WAKE_Q(wake_q);
1911 * If the operation was successful, then do
1912 * the required updates.
1915 do_smart_update(sma, sops, nsops, 1, &wake_q);
1917 set_semotime(sma, sops);
1919 sem_unlock(sma, locknum);
1925 if (error < 0) /* non-blocking error path */
1926 goto out_unlock_free;
1929 * We need to sleep on this operation, so we put the current
1930 * task into the pending queue and go to sleep.
1934 curr = &sma->sem_base[sops->sem_num];
1937 if (sma->complex_count) {
1938 list_add_tail(&queue.list,
1939 &sma->pending_alter);
1942 list_add_tail(&queue.list,
1943 &curr->pending_alter);
1946 list_add_tail(&queue.list, &curr->pending_const);
1949 if (!sma->complex_count)
1953 list_add_tail(&queue.list, &sma->pending_alter);
1955 list_add_tail(&queue.list, &sma->pending_const);
1957 sma->complex_count++;
1961 queue.status = -EINTR;
1962 queue.sleeper = current;
1964 __set_current_state(TASK_INTERRUPTIBLE);
1965 sem_unlock(sma, locknum);
1969 jiffies_left = schedule_timeout(jiffies_left);
1974 * fastpath: the semop has completed, either successfully or
1975 * not, from the syscall pov, is quite irrelevant to us at this
1976 * point; we're done.
1978 * We _do_ care, nonetheless, about being awoken by a signal or
1979 * spuriously. The queue.status is checked again in the
1980 * slowpath (aka after taking sem_lock), such that we can detect
1981 * scenarios where we were awakened externally, during the
1982 * window between wake_q_add() and wake_up_q().
1984 error = READ_ONCE(queue.status);
1985 if (error != -EINTR) {
1987 * User space could assume that semop() is a memory
1988 * barrier: Without the mb(), the cpu could
1989 * speculatively read in userspace stale data that was
1990 * overwritten by the previous owner of the semaphore.
1997 locknum = sem_lock(sma, sops, nsops);
1999 if (!ipc_valid_object(&sma->sem_perm))
2000 goto out_unlock_free;
2002 error = READ_ONCE(queue.status);
2005 * If queue.status != -EINTR we are woken up by another process.
2006 * Leave without unlink_queue(), but with sem_unlock().
2008 if (error != -EINTR)
2009 goto out_unlock_free;
2012 * If an interrupt occurred we have to clean up the queue.
2014 if (timeout && jiffies_left == 0)
2016 } while (error == -EINTR && !signal_pending(current)); /* spurious */
2018 unlink_queue(sma, &queue);
2021 sem_unlock(sma, locknum);
2024 if (sops != fast_sops)
2029 SYSCALL_DEFINE3(semop, int, semid, struct sembuf __user *, tsops,
2032 return sys_semtimedop(semid, tsops, nsops, NULL);
2035 /* If CLONE_SYSVSEM is set, establish sharing of SEM_UNDO state between
2036 * parent and child tasks.
2039 int copy_semundo(unsigned long clone_flags, struct task_struct *tsk)
2041 struct sem_undo_list *undo_list;
2044 if (clone_flags & CLONE_SYSVSEM) {
2045 error = get_undo_list(&undo_list);
2048 atomic_inc(&undo_list->refcnt);
2049 tsk->sysvsem.undo_list = undo_list;
2051 tsk->sysvsem.undo_list = NULL;
2057 * add semadj values to semaphores, free undo structures.
2058 * undo structures are not freed when semaphore arrays are destroyed
2059 * so some of them may be out of date.
2060 * IMPLEMENTATION NOTE: There is some confusion over whether the
2061 * set of adjustments that needs to be done should be done in an atomic
2062 * manner or not. That is, if we are attempting to decrement the semval
2063 * should we queue up and wait until we can do so legally?
2064 * The original implementation attempted to do this (queue and wait).
2065 * The current implementation does not do so. The POSIX standard
2066 * and SVID should be consulted to determine what behavior is mandated.
2068 void exit_sem(struct task_struct *tsk)
2070 struct sem_undo_list *ulp;
2072 ulp = tsk->sysvsem.undo_list;
2075 tsk->sysvsem.undo_list = NULL;
2077 if (!atomic_dec_and_test(&ulp->refcnt))
2081 struct sem_array *sma;
2082 struct sem_undo *un;
2084 DEFINE_WAKE_Q(wake_q);
2089 un = list_entry_rcu(ulp->list_proc.next,
2090 struct sem_undo, list_proc);
2091 if (&un->list_proc == &ulp->list_proc) {
2093 * We must wait for freeary() before freeing this ulp,
2094 * in case we raced with last sem_undo. There is a small
2095 * possibility where we exit while freeary() didn't
2096 * finish unlocking sem_undo_list.
2098 spin_unlock_wait(&ulp->lock);
2102 spin_lock(&ulp->lock);
2104 spin_unlock(&ulp->lock);
2106 /* exit_sem raced with IPC_RMID, nothing to do */
2112 sma = sem_obtain_object_check(tsk->nsproxy->ipc_ns, semid);
2113 /* exit_sem raced with IPC_RMID, nothing to do */
2119 sem_lock(sma, NULL, -1);
2120 /* exit_sem raced with IPC_RMID, nothing to do */
2121 if (!ipc_valid_object(&sma->sem_perm)) {
2122 sem_unlock(sma, -1);
2126 un = __lookup_undo(ulp, semid);
2128 /* exit_sem raced with IPC_RMID+semget() that created
2129 * exactly the same semid. Nothing to do.
2131 sem_unlock(sma, -1);
2136 /* remove un from the linked lists */
2137 ipc_assert_locked_object(&sma->sem_perm);
2138 list_del(&un->list_id);
2140 /* we are the last process using this ulp, acquiring ulp->lock
2141 * isn't required. Besides that, we are also protected against
2142 * IPC_RMID as we hold sma->sem_perm lock now
2144 list_del_rcu(&un->list_proc);
2146 /* perform adjustments registered in un */
2147 for (i = 0; i < sma->sem_nsems; i++) {
2148 struct sem *semaphore = &sma->sem_base[i];
2149 if (un->semadj[i]) {
2150 semaphore->semval += un->semadj[i];
2152 * Range checks of the new semaphore value,
2153 * not defined by sus:
2154 * - Some unices ignore the undo entirely
2155 * (e.g. HP UX 11i 11.22, Tru64 V5.1)
2156 * - some cap the value (e.g. FreeBSD caps
2157 * at 0, but doesn't enforce SEMVMX)
2159 * Linux caps the semaphore value, both at 0
2162 * Manfred <manfred@colorfullife.com>
2164 if (semaphore->semval < 0)
2165 semaphore->semval = 0;
2166 if (semaphore->semval > SEMVMX)
2167 semaphore->semval = SEMVMX;
2168 semaphore->sempid = task_tgid_vnr(current);
2171 /* maybe some queued-up processes were waiting for this */
2172 do_smart_update(sma, NULL, 0, 1, &wake_q);
2173 sem_unlock(sma, -1);
2182 #ifdef CONFIG_PROC_FS
2183 static int sysvipc_sem_proc_show(struct seq_file *s, void *it)
2185 struct user_namespace *user_ns = seq_user_ns(s);
2186 struct sem_array *sma = it;
2190 * The proc interface isn't aware of sem_lock(), it calls
2191 * ipc_lock_object() directly (in sysvipc_find_ipc).
2192 * In order to stay compatible with sem_lock(), we must
2193 * enter / leave complex_mode.
2195 complexmode_enter(sma);
2197 sem_otime = get_semotime(sma);
2200 "%10d %10d %4o %10u %5u %5u %5u %5u %10lu %10lu\n",
2205 from_kuid_munged(user_ns, sma->sem_perm.uid),
2206 from_kgid_munged(user_ns, sma->sem_perm.gid),
2207 from_kuid_munged(user_ns, sma->sem_perm.cuid),
2208 from_kgid_munged(user_ns, sma->sem_perm.cgid),
2212 complexmode_tryleave(sma);