[PATCH 4.19 071/114] sched/membarrier: Fix private expedited registration check

[Greg Kroah-Hartman]

From: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>

[ Upstream commit fc0d77387cb5ae883fd774fc559e056a8dde024c ]

Fix a logic flaw in the way membarrier_register_private_expedited()
handles ready state checks for private expedited sync core and private
expedited registrations.

If a private expedited membarrier registration is first performed, and
then a private expedited sync_core registration is performed, the ready
state check will skip the second registration when it really should not.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Chris Metcalf <cmetcalf@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Kirill Tkhai <tkhai@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Russell King - ARM Linux admin <linux@xxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20190919173705.2181-2-mathieu.desnoyers@xxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 kernel/sched/membarrier.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
index 76e0eaf4654e0..dd27e632b1bab 100644
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c
@@ -235,7 +235,7 @@ static int membarrier_register_private_expedited(int flags)
 	 * groups, which use the same mm. (CLONE_VM but not
 	 * CLONE_THREAD).
 	 */
-	if (atomic_read(&mm->membarrier_state) & state)
+	if ((atomic_read(&mm->membarrier_state) & state) == state)
 		return 0;
 	atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED, &mm->membarrier_state);
 	if (flags & MEMBARRIER_FLAG_SYNC_CORE)
-- 
2.20.1