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 08:45:46 -0600 [thread overview]
Message-ID: <23b58871-b8b6-9f5c-2a7b-f4bade6dee6e@kernel.dk> (raw)
In-Reply-To: <20200811144419.blu4wufu7t4dfqin@steredhat>
On 8/11/20 8:44 AM, Stefano Garzarella wrote:
> On Tue, Aug 11, 2020 at 08:21:12AM -0600, Jens Axboe wrote:
>> 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.
>
> Right, the only one seems io_iopoll_complete().
>
> So, IIUC, in this case we are actively polling the level below,
> so there shouldn't be any asynchronous events, is it right?
Right, that's serialized by itself.
--
Jens Axboe
prev parent reply other threads:[~2020-08-11 14:45 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
2020-08-11 14:44 ` Stefano Garzarella
2020-08-11 14:45 ` Jens Axboe [this message]
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