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authorManfred Spraul <manfred@colorfullife.com>2013-09-30 13:45:06 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-09-30 14:31:01 -0700
commit6d07b68ce16ae9535955ba2059dedba5309c3ca1 (patch)
treef8eccb1e9ff34ffb41225d247329d7e73148b6fe /ipc
parent5e9d527591421ccdb16acb8c23662231135d8686 (diff)
downloadlinux-6d07b68ce16ae9535955ba2059dedba5309c3ca1.tar.gz
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: Manfred Spraul <manfred@colorfullife.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Rik van Riel <riel@redhat.com> Reviewed-by: Davidlohr Bueso <davidlohr@hp.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'ipc')
-rw-r--r--ipc/sem.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/ipc/sem.c b/ipc/sem.c
index 4a92c0447ad..e20658d76bb 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -257,12 +257,20 @@ static void sem_rcu_free(struct rcu_head *head)
* Caller must own sem_perm.lock.
* New simple ops cannot start, because simple ops first check
* 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)
{
int i;
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++) {
sem = sma->sem_base + i;
spin_unlock_wait(&sem->lock);