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Subject: Re: [syzbot] possible deadlock in loop_add
To:     Christoph Hellwig <hch@lst.de>, Hillf Danton <hdanton@sina.com>
Cc:     syzbot <syzbot+118992efda475c16dfb0@syzkaller.appspotmail.com>,
        axboe@kernel.dk, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
        Miquel Raynal <miquel.raynal@bootlin.com>
References: <000000000000ec01e405c6c2cee3@google.com>
 <20210710131638.605-1-hdanton@sina.com> <20210712052740.GA8599@lst.de>
From:   Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Message-ID: <c3d4ebd5-5679-cd81-d1de-4f5f2cbe13db@gmail.com>
Date:   Mon, 12 Jul 2021 16:29:16 +0800
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On 12/7/21 1:27 pm, Christoph Hellwig wrote:
> On Sat, Jul 10, 2021 at 09:16:38PM +0800, Hillf Danton wrote:
>> To break the lock chain, un/register blkdev without mtd_table_mutex held.
> 
> Yes, Desmond Cheong Zhi Xi sent pretty much the same patch on June 18th
> (mtd: break circular locks in register_mtd_blktrans), but it did not get
> picked up.
> 

I believe Miqu?l was waiting for -rc1 to apply it.

But taking a closer look, although the fix for the register path is the 
same, Hillf Danton's proposed patch additionally avoids inverting the 
lock hierarchy on the unregister path. So I believe this new patch 
should be more robust.

Best wishes,
Desmond