diff options
Diffstat (limited to 'ipc/sem.c')
| -rw-r--r-- | ipc/sem.c | 211 |
1 files changed, 151 insertions, 60 deletions
@@ -95,7 +95,10 @@ struct sem { int semval; /* current value */ int sempid; /* pid of last operation */ spinlock_t lock; /* spinlock for fine-grained semtimedop */ - struct list_head sem_pending; /* pending single-sop operations */ + struct list_head pending_alter; /* pending single-sop operations */ + /* that alter the semaphore */ + struct list_head pending_const; /* pending single-sop operations */ + /* that do not alter the semaphore*/ } ____cacheline_aligned_in_smp; /* One queue for each sleeping process in the system. */ @@ -152,7 +155,7 @@ static int sysvipc_sem_proc_show(struct seq_file *s, void *it); /* * linked list protection: * sem_undo.id_next, - * sem_array.sem_pending{,last}, + * sem_array.pending{_alter,_cont}, * sem_array.sem_undo: sem_lock() for read/write * sem_undo.proc_next: only "current" is allowed to read/write that field. * @@ -337,7 +340,7 @@ static inline void sem_rmid(struct ipc_namespace *ns, struct sem_array *s) * Without the check/retry algorithm a lockless wakeup is possible: * - queue.status is initialized to -EINTR before blocking. * - wakeup is performed by - * * unlinking the queue entry from sma->sem_pending + * * unlinking the queue entry from the pending list * * setting queue.status to IN_WAKEUP * This is the notification for the blocked thread that a * result value is imminent. @@ -418,12 +421,14 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params) sma->sem_base = (struct sem *) &sma[1]; for (i = 0; i < nsems; i++) { - INIT_LIST_HEAD(&sma->sem_base[i].sem_pending); + INIT_LIST_HEAD(&sma->sem_base[i].pending_alter); + INIT_LIST_HEAD(&sma->sem_base[i].pending_const); spin_lock_init(&sma->sem_base[i].lock); } sma->complex_count = 0; - INIT_LIST_HEAD(&sma->sem_pending); + INIT_LIST_HEAD(&sma->pending_alter); + INIT_LIST_HEAD(&sma->pending_const); INIT_LIST_HEAD(&sma->list_id); sma->sem_nsems = nsems; sma->sem_ctime = get_seconds(); @@ -609,60 +614,132 @@ static void unlink_queue(struct sem_array *sma, struct sem_queue *q) * update_queue is O(N^2) when it restarts scanning the whole queue of * waiting operations. Therefore this function checks if the restart is * really necessary. It is called after a previously waiting operation - * was completed. + * modified the array. + * Note that wait-for-zero operations are handled without restart. */ static int check_restart(struct sem_array *sma, struct sem_queue *q) { - struct sem *curr; - struct sem_queue *h; - - /* if the operation didn't modify the array, then no restart */ - if (q->alter == 0) - return 0; - - /* pending complex operations are too difficult to analyse */ - if (sma->complex_count) + /* pending complex alter operations are too difficult to analyse */ + if (!list_empty(&sma->pending_alter)) return 1; /* we were a sleeping complex operation. Too difficult */ if (q->nsops > 1) return 1; - curr = sma->sem_base + q->sops[0].sem_num; + /* It is impossible that someone waits for the new value: + * - complex operations always restart. + * - wait-for-zero are handled seperately. + * - q is a previously sleeping simple operation that + * altered the array. It must be a decrement, because + * simple increments never sleep. + * - If there are older (higher priority) decrements + * in the queue, then they have observed the original + * semval value and couldn't proceed. The operation + * decremented to value - thus they won't proceed either. + */ + return 0; +} - /* No-one waits on this queue */ - if (list_empty(&curr->sem_pending)) - return 0; +/** + * wake_const_ops(sma, semnum, pt) - Wake up non-alter tasks + * @sma: semaphore array. + * @semnum: semaphore that was modified. + * @pt: list head for the tasks that must be woken up. + * + * wake_const_ops must be called after a semaphore in a semaphore array + * was set to 0. If complex const operations are pending, wake_const_ops must + * be called with semnum = -1, as well as with the number of each modified + * semaphore. + * The tasks that must be woken up are added to @pt. The return code + * is stored in q->pid. + * The function returns 1 if at least one operation was completed successfully. + */ +static int wake_const_ops(struct sem_array *sma, int semnum, + struct list_head *pt) +{ + struct sem_queue *q; + struct list_head *walk; + struct list_head *pending_list; + int semop_completed = 0; + + if (semnum == -1) + pending_list = &sma->pending_const; + else + pending_list = &sma->sem_base[semnum].pending_const; - /* the new semaphore value */ - if (curr->semval) { - /* It is impossible that someone waits for the new value: - * - q is a previously sleeping simple operation that - * altered the array. It must be a decrement, because - * simple increments never sleep. - * - The value is not 0, thus wait-for-zero won't proceed. - * - If there are older (higher priority) decrements - * in the queue, then they have observed the original - * semval value and couldn't proceed. The operation - * decremented to value - thus they won't proceed either. + walk = pending_list->next; + while (walk != pending_list) { + int error; + + q = container_of(walk, struct sem_queue, list); + walk = walk->next; + + error = try_atomic_semop(sma, q->sops, q->nsops, + q->undo, q->pid); + + if (error <= 0) { + /* operation completed, remove from queue & wakeup */ + + unlink_queue(sma, q); + + wake_up_sem_queue_prepare(pt, q, error); + if (error == 0) + semop_completed = 1; + } + } + return semop_completed; +} + +/** + * do_smart_wakeup_zero(sma, sops, nsops, pt) - wakeup all wait for zero tasks + * @sma: semaphore array + * @sops: operations that were performed + * @nsops: number of operations + * @pt: list head of the tasks that must be woken up. + * + * do_smart_wakeup_zero() checks all required queue for wait-for-zero + * operations, based on the actual changes that were performed on the + * semaphore array. + * The function returns 1 if at least one operation was completed successfully. + */ +static int do_smart_wakeup_zero(struct sem_array *sma, struct sembuf *sops, + int nsops, struct list_head *pt) +{ + int i; + int semop_completed = 0; + int got_zero = 0; + + /* first: the per-semaphore queues, if known */ + if (sops) { + for (i = 0; i < nsops; i++) { + int num = sops[i].sem_num; + + if (sma->sem_base[num].semval == 0) { + got_zero = 1; + semop_completed |= wake_const_ops(sma, num, pt); + } + } + } else { + /* + * No sops means modified semaphores not known. + * Assume all were changed. */ - BUG_ON(q->sops[0].sem_op >= 0); - return 0; + for (i = 0; i < sma->sem_nsems; i++) { + if (sma->sem_base[i].semval == 0) { + got_zero = 1; + semop_completed |= wake_const_ops(sma, i, pt); + } + } } /* - * semval is 0. Check if there are wait-for-zero semops. - * They must be the first entries in the per-semaphore queue + * If one of the modified semaphores got 0, + * then check the global queue, too. */ - h = list_first_entry(&curr->sem_pending, struct sem_queue, list); - BUG_ON(h->nsops != 1); - BUG_ON(h->sops[0].sem_num != q->sops[0].sem_num); + if (got_zero) + semop_completed |= wake_const_ops(sma, -1, pt); - /* Yes, there is a wait-for-zero semop. Restart */ - if (h->sops[0].sem_op == 0) - return 1; - - /* Again - no-one is waiting for the new value. */ - return 0; + return semop_completed; } @@ -678,6 +755,8 @@ static int check_restart(struct sem_array *sma, struct sem_queue *q) * semaphore. * The tasks that must be woken up are added to @pt. The return code * is stored in q->pid. + * The function internally checks if const operations can now succeed. + * * The function return 1 if at least one semop was completed successfully. */ static int update_queue(struct sem_array *sma, int semnum, struct list_head *pt) @@ -688,9 +767,9 @@ static int update_queue(struct sem_array *sma, int semnum, struct list_head *pt) int semop_completed = 0; if (semnum == -1) - pending_list = &sma->sem_pending; + pending_list = &sma->pending_alter; else - pending_list = &sma->sem_base[semnum].sem_pending; + pending_list = &sma->sem_base[semnum].pending_alter; again: walk = pending_list->next; @@ -702,13 +781,12 @@ again: /* If we are scanning the single sop, per-semaphore list of * one semaphore and that semaphore is 0, then it is not - * necessary to scan the "alter" entries: simple increments + * necessary to scan further: simple increments * that affect only one entry succeed immediately and cannot * be in the per semaphore pending queue, and decrements * cannot be successful if the value is already 0. */ - if (semnum != -1 && sma->sem_base[semnum].semval == 0 && - q->alter) + if (semnum != -1 && sma->sem_base[semnum].semval == 0) break; error = try_atomic_semop(sma, q->sops, q->nsops, @@ -724,6 +802,7 @@ again: restart = 0; } else { semop_completed = 1; + do_smart_wakeup_zero(sma, q->sops, q->nsops, pt); restart = check_restart(sma, q); } @@ -742,8 +821,8 @@ again: * @otime: force setting otime * @pt: list head of the tasks that must be woken up. * - * do_smart_update() does the required called to update_queue, based on the - * actual changes that were performed on the semaphore array. + * do_smart_update() does the required calls to update_queue and wakeup_zero, + * based on the actual changes that were performed on the semaphore array. * Note that the function does not do the actual wake-up: the caller is * responsible for calling wake_up_sem_queue_do(@pt). * It is safe to perform this call after dropping all locks. @@ -754,6 +833,8 @@ static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsop int i; int progress; + otime |= do_smart_wakeup_zero(sma, sops, nsops, pt); + progress = 1; retry_global: if (sma->complex_count) { @@ -813,14 +894,14 @@ static int count_semncnt (struct sem_array * sma, ushort semnum) struct sem_queue * q; semncnt = 0; - list_for_each_entry(q, &sma->sem_base[semnum].sem_pending, list) { + list_for_each_entry(q, &sma->sem_base[semnum].pending_alter, list) { struct sembuf * sops = q->sops; BUG_ON(sops->sem_num != semnum); if ((sops->sem_op < 0) && !(sops->sem_flg & IPC_NOWAIT)) semncnt++; } - list_for_each_entry(q, &sma->sem_pending, list) { + list_for_each_entry(q, &sma->pending_alter, list) { struct sembuf * sops = q->sops; int nsops = q->nsops; int i; @@ -839,14 +920,14 @@ static int count_semzcnt (struct sem_array * sma, ushort semnum) struct sem_queue * q; semzcnt = 0; - list_for_each_entry(q, &sma->sem_base[semnum].sem_pending, list) { + list_for_each_entry(q, &sma->sem_base[semnum].pending_const, list) { struct sembuf * sops = q->sops; BUG_ON(sops->sem_num != semnum); if ((sops->sem_op == 0) && !(sops->sem_flg & IPC_NOWAIT)) semzcnt++; } - list_for_each_entry(q, &sma->sem_pending, list) { + list_for_each_entry(q, &sma->pending_const, list) { struct sembuf * sops = q->sops; int nsops = q->nsops; int i; @@ -884,13 +965,22 @@ static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp) /* Wake up all pending processes and let them fail with EIDRM. */ INIT_LIST_HEAD(&tasks); - list_for_each_entry_safe(q, tq, &sma->sem_pending, list) { + list_for_each_entry_safe(q, tq, &sma->pending_const, list) { + unlink_queue(sma, q); + wake_up_sem_queue_prepare(&tasks, q, -EIDRM); + } + + list_for_each_entry_safe(q, tq, &sma->pending_alter, list) { unlink_queue(sma, q); wake_up_sem_queue_prepare(&tasks, q, -EIDRM); } for (i = 0; i < sma->sem_nsems; i++) { struct sem *sem = sma->sem_base + i; - list_for_each_entry_safe(q, tq, &sem->sem_pending, list) { + list_for_each_entry_safe(q, tq, &sem->pending_const, list) { + unlink_queue(sma, q); + wake_up_sem_queue_prepare(&tasks, q, -EIDRM); + } + list_for_each_entry_safe(q, tq, &sem->pending_alter, list) { unlink_queue(sma, q); wake_up_sem_queue_prepare(&tasks, q, -EIDRM); } @@ -1658,14 +1748,15 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops, curr = &sma->sem_base[sops->sem_num]; if (alter) - list_add_tail(&queue.list, &curr->sem_pending); + list_add_tail(&queue.list, &curr->pending_alter); else - list_add(&queue.list, &curr->sem_pending); + list_add_tail(&queue.list, &curr->pending_const); } else { if (alter) - list_add_tail(&queue.list, &sma->sem_pending); + list_add_tail(&queue.list, &sma->pending_alter); else - list_add(&queue.list, &sma->sem_pending); + list_add_tail(&queue.list, &sma->pending_const); + sma->complex_count++; } |
