Commit 6d07b68c authored by Manfred Spraul's avatar Manfred Spraul Committed by Linus Torvalds

ipc/sem.c: optimize sem_lock()

Operations that need access to the whole array must guarantee that there
are no simple operations ongoing.  Right now this is achieved by
spin_unlock_wait(sem->lock) on all semaphores.

If complex_count is nonzero, then this spin_unlock_wait() is not
necessary, because it was already performed in the past by the thread
that increased complex_count and even though sem_perm.lock was dropped
inbetween, no simple operation could have started, because simple
operations cannot start when complex_count is non-zero.
Signed-off-by: default avatarManfred Spraul <manfred@colorfullife.com>
Cc: Mike Galbraith <bitbucket@online.de>
Cc: Rik van Riel <riel@redhat.com>
Reviewed-by: default avatarDavidlohr Bueso <davidlohr@hp.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5e9d5275
...@@ -257,12 +257,20 @@ static void sem_rcu_free(struct rcu_head *head) ...@@ -257,12 +257,20 @@ static void sem_rcu_free(struct rcu_head *head)
* Caller must own sem_perm.lock. * Caller must own sem_perm.lock.
* New simple ops cannot start, because simple ops first check * New simple ops cannot start, because simple ops first check
* that sem_perm.lock is free. * that sem_perm.lock is free.
* that a) sem_perm.lock is free and b) complex_count is 0.
*/ */
static void sem_wait_array(struct sem_array *sma) static void sem_wait_array(struct sem_array *sma)
{ {
int i; int i;
struct sem *sem; struct sem *sem;
if (sma->complex_count) {
/* The thread that increased sma->complex_count waited on
* all sem->lock locks. Thus we don't need to wait again.
*/
return;
}
for (i = 0; i < sma->sem_nsems; i++) { for (i = 0; i < sma->sem_nsems; i++) {
sem = sma->sem_base + i; sem = sma->sem_base + i;
spin_unlock_wait(&sem->lock); spin_unlock_wait(&sem->lock);
......
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