On Thu, Apr 25, 2019 at 02:30:35AM +0900, Tetsuo Handa wrote:
On 2019/04/25 2:08, Greg Kroah-Hartman wrote:
[ 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().
Excuse me?
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 fb90ca3a296e..27de98428367 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -3312,6 +3312,9 @@ __lock_set_class(struct lockdep_map *lock, const char *name, unsigned int depth; int i;
- if (unlikely(!debug_locks))
return 0;This is __lock_set_class() function rather than __lock_downgrade() function. __lock_downgrade() is available in 4.12+.
For 3.18-stable, downgrade_write() is in kernel/locking/rwsem.c . Therefore, we should check whether adding this check into __lock_set_class() is what we want to do...
Ugh, this got backported incorrectly to 4.4.y as well, let me check 4.9.y... Yup, that's wrong too.
As is 4.14.y.
As is 4.19.y.
Hey, I got it right in 5.0.y!
Ok, let me go drop this 3.18.y patch, and revert it from all of the other trees for now as well, thanks for catching this.
greg k-h