linux-kernel - Re: [syzbot] possible deadlock in loop

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Date:   Fri, 16 Jul 2021 01:00:28 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
Cc:     Christoph Hellwig <hch@....de>, Hillf Danton <hdanton@...a.com>,
        syzbot <syzbot+118992efda475c16dfb0@...kaller.appspotmail.com>,
        axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] possible deadlock in loop_add

Hello,

Desmond Cheong Zhi Xi <desmondcheongzx@...il.com> wrote on Mon, 12 Jul
2021 16:29:16 +0800:

> 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 Miquèl was waiting for -rc1 to apply it.

Indeed, I already applied it but did not advertise yet.

> 
> 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.

We can definitely do this in two steps if you want.

Thanks,
Miquèl