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[BACKPORT,4.19.y,1/3] locking/lockdep: Add debug_locks check in __lock_downgrade()

Message ID ee8b45ecc3060ea0e00ba8015dcd6073496ceb6d.1569404757.git.baolin.wang@linaro.org
State New
Headers show
Series [BACKPORT,4.19.y,1/3] locking/lockdep: Add debug_locks check in __lock_downgrade() | expand

Commit Message

(Exiting) Baolin Wang Sept. 25, 2019, 9:53 a.m. UTC 
From: Waiman Long <longman@redhat.com>


[Upstream commit 513e1073d52e55b8024b4f238a48de7587c64ccf]

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
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Patch

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index e810e8c..1e272f6 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3605,6 +3605,9 @@  static int __lock_downgrade(struct lockdep_map *lock, unsigned long ip)
 	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,