shm: optimize exit_shm()

We may optimistically check .in_use == 0 without holding the rw_mutex: it's the common case, and if it's zero, there certainly won't be any segments associated with us. After taking the lock, the idr_for_each() will do the right thing, so we could now drop the re-check inside the lock without any real cost. But it won't hurt. Signed-off-by: Vasiliy Kulikov <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
ambv · Aug 4, 2011 · 298507d · 298507d
1 parent 33a30ed
commit 298507d
Showing 1 changed file with 3 additions and 0 deletions.
diff --git a/ipc/shm.c b/ipc/shm.c
@@ -304,6 +304,9 @@ void exit_shm(struct task_struct *task)
 {
 	struct ipc_namespace *ns = task->nsproxy->ipc_ns;
 
+	if (shm_ids(ns).in_use == 0)
+		return;
+
 	/* Destroy all already created segments, but not mapped yet */
 	down_write(&shm_ids(ns).rw_mutex);
 	if (shm_ids(ns).in_use)