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From: Chris Wilson <chris@chris-wilson.co.uk>
To: linux-kernel@vger.kernel.org
Cc: Chris Wilson <chris@chris-wilson.co.uk>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Daniel Vetter <daniel.vetter@ffwll.ch>
Subject: [PATCH] mutex: Always clear owner field upon mutex_unlock()
Date: Tue,  6 Jan 2015 10:29:35 +0000
Message-ID: <1420540175-30204-1-git-send-email-chris@chris-wilson.co.uk> (raw)

Currently if DEBUG_MUTEXES is enabled, the mutex->owner field is only
cleared iff debug_locks is active. This exposes a race to other users of
the field where the mutex->owner may be still set to a stale value,
potentially upsetting mutex_spin_on_owner() among others.

References: https://bugs.freedesktop.org/show_bug.cgi?id=87955
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 kernel/locking/mutex-debug.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
index 5cf6731b98e9..3ef3736002d8 100644
--- a/kernel/locking/mutex-debug.c
+++ b/kernel/locking/mutex-debug.c
@@ -80,13 +80,13 @@ void debug_mutex_unlock(struct mutex *lock)
 			DEBUG_LOCKS_WARN_ON(lock->owner != current);
 
 		DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next);
-		mutex_clear_owner(lock);
 	}
 
 	/*
 	 * __mutex_slowpath_needs_to_unlock() is explicitly 0 for debug
 	 * mutexes so that we can do it here after we've verified state.
 	 */
+	mutex_clear_owner(lock);
 	atomic_set(&lock->count, 1);
 }
 
-- 
2.1.4


             reply index

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-06 10:29 Chris Wilson [this message]
2015-01-06 11:34 ` Peter Zijlstra
2015-01-06 16:43 ` Davidlohr Bueso
2015-01-09 12:34 ` [tip:locking/urgent] " tip-bot for Chris Wilson

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