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Subject: Re: [syzbot] WARNING in io_wqe_enqueue
To:     Dmitry Vyukov <dvyukov@google.com>
Cc:     syzbot <syzbot+ea2f1484cffe5109dc10@syzkaller.appspotmail.com>,
        Pavel Begunkov <asml.silence@gmail.com>,
        Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Al Viro <viro@zeniv.linux.org.uk>
References: <0000000000000bdfa905c3f6720f@google.com>
 <b9cb6dc4-3dfe-de60-a933-1f423301b3ca@linux.alibaba.com>
 <CACT4Y+az0ZsTRyj+FjA08ZjpoesoxSde+1vxn-WQnTgXM1rPGQ@mail.gmail.com>
From:   Hao Xu <haoxu@linux.alibaba.com>
Message-ID: <b38c580a-2f74-39ee-706a-13eab4e16d1c@linux.alibaba.com>
Date:   Thu, 10 Jun 2021 11:03:46 +0800
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在 2021/6/8 下午8:01, Dmitry Vyukov 写道:
> On Tue, Jun 8, 2021 at 11:47 AM Hao Xu <haoxu@linux.alibaba.com> wrote:
>>
>> 在 2021/6/5 上午4:22, syzbot 写道:
>>> syzbot has bisected this issue to:
>>>
>>> commit 24369c2e3bb06d8c4e71fd6ceaf4f8a01ae79b7c
>>> Author: Pavel Begunkov <asml.silence@gmail.com>
>>> Date:   Tue Jan 28 00:15:48 2020 +0000
>>>
>>>       io_uring: add io-wq workqueue sharing
>>>
>>> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=17934777d00000
>>> start commit:   f88cd3fb Merge tag 'vfio-v5.13-rc5' of git://github.com/aw..
>>> git tree:       upstream
>>> final oops:     https://syzkaller.appspot.com/x/report.txt?x=14534777d00000
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=10534777d00000
>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=82d85e75046e5e64
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=ea2f1484cffe5109dc10
>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16d5772fd00000
>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10525947d00000
>>>
>>> Reported-by: syzbot+ea2f1484cffe5109dc10@syzkaller.appspotmail.com
>>> Fixes: 24369c2e3bb0 ("io_uring: add io-wq workqueue sharing")
>>>
>>> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
>>>
>> This is not a bug, the repro program first set RLIMIT_NPROC to 0, then
>> submits an unbound work whcih raises a warning of
>> WARN_ON_ONCE(!acct->max_workers). Since unbound->max_workers is
>> task_rlimit(current, RLIMIT_NPROC), so it is expected.
> 
> Hi Hao,
> 
> Then this is a mis-use of WARN_ON. If this check is intended for end
> users, it needs to use pr_err (also print understandable message and
> no stack trace which is most likely not useful for end users):
> https://elixir.bootlin.com/linux/v5.13-rc5/source/include/asm-generic/bug.h#L71
>
  Agree, pr_err/pr_warn is better here.