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Commit 59da7942 authored by Waiman Long's avatar Waiman Long Committed by Greg Kroah-Hartman
Browse files

locking/lockdep: Add debug_locks check in __lock_downgrade() 



[ 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: default avatarTetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Reported-by: default avatar <syzbot+53383ae265fb161ef488@syzkaller.appspotmail.com>
Signed-off-by: default avatarWaiman Long <longman@redhat.com>
Signed-off-by: default avatarPeter 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: default avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 9ad66b78

kernel/locking/lockdep.c

+3 −0
Original line number Diff line number Diff line
@@ -3446,6 +3446,9 @@ __lock_set_class(struct lockdep_map *lock, const char *name, 
	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,