linux-kernel - Re: [PATCH 4.19 36/63] locking/lockdep: Add debug_locks check in __lock

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Message-ID: <20190930002828.GQ8171@sasha-vm>
Date:   Sun, 29 Sep 2019 20:28:28 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        syzbot+53383ae265fb161ef488@...kaller.appspotmail.com,
        Waiman Long <longman@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will.deacon@....com>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 4.19 36/63] locking/lockdep: Add debug_locks check in
 __lock_downgrade()

On Sun, Sep 29, 2019 at 11:43:38PM +0900, Tetsuo Handa wrote:
>On 2019/09/29 22:54, Greg Kroah-Hartman wrote:
>> From: Waiman Long <longman@...hat.com>
>>
>> [ Upstream commit 513e1073d52e55b8024b4f238a48de7587c64ccf ]
>>
>> 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().
>
>Please drop "[PATCH 4.19 36/63] locking/lockdep: Add debug_locks check in __lock_downgrade()".
>We had a revert patch shown below in the past.

We had a revert in the stable trees, but that revert was incorrect.

Take a look at commit 513e1073d52e55 upstream, it patches
__lock_set_class() (even though the subject line says
__lock_downgrade()). So this is not a backporting error as the revert
said it is, but is rather the intended location to be patched.

If this is actually wrong, then it should be addressed upstream first.

--
Thanks,
Sasha