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

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Message-ID: <20190930113557.GR8171@sasha-vm>
Date:   Mon, 30 Sep 2019 07:35:57 -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 Mon, Sep 30, 2019 at 10:46:39AM +0900, Tetsuo Handa wrote:
>On 2019/09/30 9:28, Sasha Levin wrote:
>> 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.
>>
>
>Hmm, upstream has two commits with same author, same date, same subject, different hash, different content.
>I couldn't find from https://lkml.kernel.org/r/1547093005-26085-1-git-send-email-longman@redhat.com that
>we want to patch both __lock_set_class() and __lock_downgrade(), but I found that the tip-bot has patched
>__lock_downgrade() on "2019-01-21 11:29" and __lock_set_class() on "2019-02-04  8:56".
>Seems that we by error patched both functions, though patching both functions should be harmless...

Right, there's a lot of confusion between the duplicate subject lines
and what this patch actually does. My point was that this is an upstream
issue rather than a stable issue, we're just aligning with upstream
here.

--
Thanks,
Sasha