From: Waiman Long longman@redhat.com
[ Upstream commit 71492580571467fb7177aade19c18ce7486267f5 ]
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: Tetsuo Handa penguin-kernel@i-love.sakura.ne.jp 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.c... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/locking/lockdep.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 68ba411a90075..1c8e5d186ad64 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -3608,6 +3608,9 @@ 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,