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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>
This commit is contained in:
Vasiliy Kulikov 2011-08-03 22:28:26 +04:00 committed by Linus Torvalds
parent 33a30ed4bd
commit 298507d4d2
1 changed files with 3 additions and 0 deletions
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3
ipc/shm.c
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@ -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)