linux-kernel - Re: [PATCH] locking/lockdep: Add debug_locks check in __lock

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Message-ID: <250f311c-a686-d4b3-d88f-6d39ff3b1492@i-love.sakura.ne.jp>
Date:   Sun, 20 Jan 2019 11:50:49 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Peter Zijlstra <peterz@...radead.org>,
        Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Waiman Long <longman@...hat.com>, Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] locking/lockdep: Add debug_locks check in
 __lock_downgrade()

Peter, will this fix be sent to linux.git shortly?
syzbot is generating many corrupted reports due to this race.

On 2019/01/14 22:36, Peter Zijlstra wrote:
> On Thu, Jan 10, 2019 at 11:21:13AM +0100, Dmitry Vyukov wrote:
>> On Thu, Jan 10, 2019 at 5:04 AM Waiman Long <longman@...hat.com> wrote:
>>>
>>> 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().
>>>
>>> Signed-off-by: Waiman Long <longman@...hat.com>
>>> Reported-by: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
>>
>> Please also add:
>>
>> Reported-by: syzbot+53383ae265fb161ef488@...kaller.appspotmail.com
>>
>> for tracking purposes. But Tetsuo deserves lots of credit for debugging it.
> 
> I made that:
> 
> Reported-by: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
> Debugged-by: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
> Reported-by: syzbot+53383ae265fb161ef488@...kaller.appspotmail.com