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Date:   Sun, 29 Sep 2019 20:28:28 -0400
From:   Sasha Levin <sashal@kernel.org>
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        syzbot+53383ae265fb161ef488@syzkaller.appspotmail.com,
        Waiman Long <longman@redhat.com>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <will.deacon@arm.com>,
        Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH 4.19 36/63] locking/lockdep: Add debug_locks check in
 __lock_downgrade()
Message-ID: <20190930002828.GQ8171@sasha-vm>
References: <20190929135031.382429403@linuxfoundation.org>
 <20190929135038.482721804@linuxfoundation.org>
 <801c81d2-ce72-8eb3-a18b-1b0943270fc4@i-love.sakura.ne.jp>
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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@redhat.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