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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Tue, 8 Jun 2021 14:01:19 +0200
Message-ID: <CACT4Y+az0ZsTRyj+FjA08ZjpoesoxSde+1vxn-WQnTgXM1rPGQ@mail.gmail.com>
Subject: Re: [syzbot] WARNING in io_wqe_enqueue
To:     Hao Xu <haoxu@linux.alibaba.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>
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On Tue, Jun 8, 2021 at 11:47 AM Hao Xu <haoxu@linux.alibaba.com> wrote:
>
> =E5=9C=A8 2021/6/5 =E4=B8=8A=E5=8D=884:22, syzbot =E5=86=99=E9=81=93:
> > 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=3D17934777=
d00000
> > 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=3D14534777=
d00000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=3D10534777d00=
000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=3D82d85e75046=
e5e64
> > dashboard link: https://syzkaller.appspot.com/bug?extid=3Dea2f1484cffe5=
109dc10
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=3D16d5772fd=
00000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=3D10525947d00=
000
> >
> > 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#bise=
ction
> >
> 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