Commit 4a195a0b authored by Waiman Long's avatar Waiman Long Committed by Greg Kroah-Hartman

locking/lockdep: Add debug_locks check in __lock_downgrade()

commit 71492580571467fb7177aade19c18ce7486267f5 upstream.

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().
Debugged-by: 's avatarTetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Reported-by: 's avatarTetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Reported-by: syzbot+53383ae265fb161ef488@syzkaller.appspotmail.com
Signed-off-by: 's avatarWaiman Long <longman@redhat.com>
Signed-off-by: 's 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.comSigned-off-by: 's avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: 's avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 5befc25f
......@@ -3650,6 +3650,9 @@ __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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