From: Jens Axboe <axboe@kernel.dk>
To: Stefano Garzarella <sgarzare@redhat.com>
Cc: syzbot <syzbot+996f91b6ec3812c48042@syzkaller.appspotmail.com>,
io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
viro@zeniv.linux.org.uk
Subject: Re: possible deadlock in __io_queue_deferred
Date: Tue, 11 Aug 2020 08:21:12 -0600 [thread overview]
Message-ID: <504b4b08-30c1-4ca8-ab3b-c9f0b58f0cfa@kernel.dk> (raw)
In-Reply-To: <20200811140010.gigc2amchytqmrkk@steredhat>
On 8/11/20 8:00 AM, Stefano Garzarella wrote:
> On Mon, Aug 10, 2020 at 09:55:17AM -0600, Jens Axboe wrote:
>> On 8/10/20 9:36 AM, syzbot wrote:
>>> Hello,
>>>
>>> syzbot found the following issue on:
>>>
>>> HEAD commit: 449dc8c9 Merge tag 'for-v5.9' of git://git.kernel.org/pub/..
>>> git tree: upstream
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=14d41e02900000
>>> kernel config: https://syzkaller.appspot.com/x/.config?x=9d25235bf0162fbc
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=996f91b6ec3812c48042
>>> compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
>>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=133c9006900000
>>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1191cb1a900000
>>>
>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>>> Reported-by: syzbot+996f91b6ec3812c48042@syzkaller.appspotmail.com
>>
>> Thanks, the below should fix this one.
>
> Yeah, it seems right to me, since only __io_queue_deferred() (invoked by
> io_commit_cqring()) can be called with 'completion_lock' held.
Right
> Just out of curiosity, while exploring the code I noticed that we call
> io_commit_cqring() always with the 'completion_lock' held, except in the
> io_poll_* functions.
>
> That's because then there can't be any concurrency?
Do you mean the iopoll functions? Because we're definitely holding it
for the io_poll_* functions.
--
Jens Axboe
next prev parent reply other threads:[~2020-08-11 14:21 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-10 15:36 possible deadlock in __io_queue_deferred syzbot
2020-08-10 15:55 ` Jens Axboe
2020-08-11 14:00 ` Stefano Garzarella
2020-08-11 14:21 ` Jens Axboe [this message]
2020-08-11 14:44 ` Stefano Garzarella
2020-08-11 14:45 ` Jens Axboe
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