Commit 513e1073 authored Jan 09, 2019 by Waiman Long Committed by Ingo Molnar Feb 04, 2019

locking/lockdep: Add debug_locks check in __lock_downgrade()



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>

parent 31fe3cbb

kernel/locking/lockdep.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -3479,6 +3479,9 @@ __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,

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