Commit 298507d4 authored Aug 03, 2011 by Vasiliy Kulikov Committed by Linus Torvalds Aug 03, 2011

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>

parent 33a30ed4

ipc/shm.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -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)