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 <>
Cc: Mike Galbraith <>
Cc: Rik van Riel <>
Reviewed-by: default avatarDavidlohr Bueso <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 5e9d5275
......@@ -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.
for (i = 0; i < sma->sem_nsems; i++) {
sem = sma->sem_base + i;
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