linux-kernel - [PATCH 2/2] ipc,sem: remove uneeded sem_undo_list lock usage in exit

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Date:	Tue, 11 Aug 2015 14:19:16 -0300
From:	"Herton R. Krzesinski" <herton@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Manfred Spraul <manfred@...orfullife.com>,
	Rafael Aquini <aquini@...hat.com>,
	Joe Perches <joe@...ches.com>,
	Aristeu Rozanski <aris@...hat.com>, djeffery@...hat.com,
	herton@...hat.com
Subject: [PATCH 2/2] ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()

After we acquire the sma->sem_perm lock in exit_sem(), we are protected against
a racing IPC_RMID operation. Also at that point, we are the last user of
sem_undo_list. Therefore it isn't required that we acquire or use ulp->lock.

Signed-off-by: Herton R. Krzesinski <herton@...hat.com>
---
 ipc/sem.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index 3b8b66b..c4c2911 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -2121,9 +2121,11 @@ void exit_sem(struct task_struct *tsk)
 		ipc_assert_locked_object(&sma->sem_perm);
 		list_del(&un->list_id);
 
-		spin_lock(&ulp->lock);
+		/* we are the last process using this ulp, acquiring ulp->lock
+		 * isn't required. Besides that, we are also protected against
+		 * IPC_RMID as we hold sma->sem_perm lock now
+		 */
 		list_del_rcu(&un->list_proc);
-		spin_unlock(&ulp->lock);
 
 		/* perform adjustments registered in un */
 		for (i = 0; i < sma->sem_nsems; i++) {
-- 
2.4.3

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