linux-kernel - Re: [PATCH next] io_uring: fix task hung in io_uring

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Message-ID: <8031fbe7-9e69-4a79-3b42-55b2a1a690e3@gmail.com>
Date:   Mon, 7 Sep 2020 11:50:48 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>, Hillf Danton <hdanton@...a.com>
Cc:     io-uring@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        viro@...iv.linux.org.uk,
        syzbot+107dd59d1efcaf3ffca4@...kaller.appspotmail.com,
        Stefano Garzarella <sgarzare@...hat.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH next] io_uring: fix task hung in io_uring_setup

On 03/09/2020 17:04, Jens Axboe wrote:
> On 9/3/20 7:21 AM, Hillf Danton wrote:
>>
>> The smart syzbot found the following issue:
>>
>> INFO: task syz-executor047:6853 blocked for more than 143 seconds.
>>       Not tainted 5.9.0-rc3-next-20200902-syzkaller #0
>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>> task:syz-executor047 state:D stack:28104 pid: 6853 ppid:  6847 flags:0x00004000
>> Call Trace:
>>  context_switch kernel/sched/core.c:3777 [inline]
>>  __schedule+0xea9/0x2230 kernel/sched/core.c:4526
>>  schedule+0xd0/0x2a0 kernel/sched/core.c:4601
>>  schedule_timeout+0x1d8/0x250 kernel/time/timer.c:1855
>>  do_wait_for_common kernel/sched/completion.c:85 [inline]
>>  __wait_for_common kernel/sched/completion.c:106 [inline]
>>  wait_for_common kernel/sched/completion.c:117 [inline]
>>  wait_for_completion+0x163/0x260 kernel/sched/completion.c:138
>>  io_sq_thread_stop fs/io_uring.c:6906 [inline]
>>  io_finish_async fs/io_uring.c:6920 [inline]
>>  io_sq_offload_create fs/io_uring.c:7595 [inline]
>>  io_uring_create fs/io_uring.c:8671 [inline]
>>  io_uring_setup+0x1495/0x29a0 fs/io_uring.c:8744
>>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>
>> because the sqo_thread kthread is created in io_sq_offload_create() without
>> being waked up. Then in the error branch of that function we will wait for
>> the sqo kthread that never runs. It's fixed by waking it up before waiting.
> 
> Looks good - applied, thanks.

BTW, I don't see the patch itself, and it's neither in io_uring, block
nor fs mailing lists. Hillf, could you please CC proper lists next time?

-- 
Pavel Begunkov