diff mbox series

[BACKPORT,4.14.y,3/8] locking/lockdep: Add debug_locks check in __lock_downgrade()

Message ID ecdae1a4a913695b66404f0d34250b6812f7c1dd.1567492316.git.baolin.wang@linaro.org
State Superseded
Headers show
Series [BACKPORT,4.14.y,1/8] drm/i915/fbdev: Actually configure untiled displays | expand

Commit Message

(Exiting) Baolin Wang Sept. 3, 2019, 6:57 a.m. UTC 
From: Waiman Long <longman@redhat.com>


Tetsuo Handa had reported he saw an incorrect "downgrading a read lock"
warning right after a previous lockdep warning. It is likely that the
previous warning turned off lock debugging causing the lockdep to have
inconsistency states leading to the lock downgrade warning.

Fix that by add a check for debug_locks at the beginning of
__lock_downgrade().

Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Reported-by: syzbot+53383ae265fb161ef488@syzkaller.appspotmail.com
Signed-off-by: Waiman Long <longman@redhat.com>

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/r/1547093005-26085-1-git-send-email-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

Signed-off-by: Baolin Wang <baolin.wang@linaro.org>

---
 kernel/locking/lockdep.c |    3 +++
 1 file changed, 3 insertions(+)

-- 
1.7.9.5
diff mbox series

Patch

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 565005a..5c370c6 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3650,6 +3650,9 @@  static int reacquire_held_locks(struct task_struct *curr, unsigned int depth,
 	unsigned int depth;
 	int i;
 
+	if (unlikely(!debug_locks))
+		return 0;
+
 	depth = curr->lockdep_depth;
 	/*
 	 * This function is about (re)setting the class of a held lock,