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 <segoon@openwall.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/ipc/shm.c b/ipc/shm.c
index 7efff04..b5bae9d 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -304,6 +304,9 @@
{
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)