diff options
| author | Manfred Spraul <manfred@colorfullife.com> | 2005-01-04 05:34:13 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@ppc970.osdl.org> | 2005-01-04 05:34:13 -0800 |
| commit | 956cdd1b90acdc646bd4c7d3066539859f8b0f62 (patch) | |
| tree | 5dafde81da9f18ce6fc60743fbf19b38b0161a4f /ipc | |
| parent | 79a35a448eed5cc795f32625946b38a8a5f595ea (diff) | |
| download | history-956cdd1b90acdc646bd4c7d3066539859f8b0f62.tar.gz | |
[PATCH] fix missing wakeup in ipc/sem
My patch that removed the spin_lock calls from the tail of sys_semtimedop
introduced a bug:
Before my patch was merged, every operation that altered an array called
update_queue. That call woke up threads that were waiting until a
semaphore value becomes 0. I've accidentially removed that call.
The attached patch fixes that by modifying update_queue: the function now
loops internally and wakes up all threads. The patch also removes
update_queue calls from the error path of sys_semtimedop: failed operations
do not modify the array, no need to rescan the list of waiting threads.
Signed-Off-By: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'ipc')
| -rw-r--r-- | ipc/sem.c | 27 |
1 files changed, 21 insertions, 6 deletions
diff --git a/ipc/sem.c b/ipc/sem.c index 7d639d9f131ed9..f0efedb8d4c303 100644 --- a/ipc/sem.c +++ b/ipc/sem.c @@ -358,8 +358,22 @@ static void update_queue (struct sem_array * sma) if (error <= 0) { struct sem_queue *n; remove_from_queue(sma,q); - n = q->next; q->status = IN_WAKEUP; + /* + * Continue scanning. The next operation + * that must be checked depends on the type of the + * completed operation: + * - if the operation modified the array, then + * restart from the head of the queue and + * check for threads that might be waiting + * for semaphore values to become 0. + * - if the operation didn't modify the array, + * then just continue. + */ + if (q->alter) + n = sma->sem_pending; + else + n = q->next; wake_up_process(q->sleeper); /* hands-off: q will disappear immediately after * writing q->status. @@ -1119,8 +1133,11 @@ retry_undos: goto out_unlock_free; error = try_atomic_semop (sma, sops, nsops, un, current->tgid); - if (error <= 0) - goto update; + if (error <= 0) { + if (alter && error == 0) + update_queue (sma); + goto out_unlock_free; + } /* We need to sleep on this operation, so we put the current * task into the pending queue and go to sleep. @@ -1132,6 +1149,7 @@ retry_undos: queue.undo = un; queue.pid = current->tgid; queue.id = semid; + queue.alter = alter; if (alter) append_to_queue(sma ,&queue); else @@ -1183,9 +1201,6 @@ retry_undos: remove_from_queue(sma,&queue); goto out_unlock_free; -update: - if (alter) - update_queue (sma); out_unlock_free: sem_unlock(sma); out_free: |