linux-kernel - Re: [syzbot] [net?] possible deadlock in inet

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Message-ID: <CANn89iKVbTKxgO=_47TU21b6GakhnRuBk2upGviCK0Y1Q2Ar2Q@mail.gmail.com>
Date: Mon, 8 Sep 2025 02:07:05 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: syzbot <syzbot+e1cd6bd8493060bd701d@...kaller.appspotmail.com>, 
	Josef Bacik <josef@...icpanda.com>, Jens Axboe <axboe@...nel.dk>, davem@...emloft.net, 
	dsahern@...nel.org, horms@...nel.org, kuba@...nel.org, 
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, 
	ming.lei@...hat.com, netdev@...r.kernel.org, pabeni@...hat.com, 
	syzkaller-bugs@...glegroups.com, thomas.hellstrom@...ux.intel.com, 
	"yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [syzbot] [net?] possible deadlock in inet_shutdown

On Mon, Sep 8, 2025 at 1:52 AM Yu Kuai <yukuai1@...weicloud.com> wrote:
>
> Hi,
>
> 在 2025/09/06 17:16, Eric Dumazet 写道:
> > On Fri, Sep 5, 2025 at 1:03 PM Eric Dumazet <edumazet@...gle.com> wrote:
> >>
> >> On Fri, Sep 5, 2025 at 1:00 PM syzbot
> >> <syzbot+e1cd6bd8493060bd701d@...kaller.appspotmail.com> wrote:
> >
> > Note to NBD maintainers : I held about  20 syzbot reports all pointing
> > to NBD accepting various sockets, I  can release them if needed, if you prefer
> > to triage them.
> >
> I'm not NBD maintainer, just trying to understand the deadlock first.
>
> Is this deadlock only possible for some sepecific socket types? Take
> a look at the report here:
>
> Usually issue IO will require the order:
>
> q_usage_counter -> cmd lock -> tx lock -> sk lock
>

I have not seen the deadlock being reported with normal TCP sockets.

NBD sets sk->sk_allocation to  GFP_NOIO | __GFP_MEMALLOC;
from __sock_xmit(), and TCP seems to respect this.