linux-kernel - Re: [syzbot] WARNING in io_wqe

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Date:   Tue, 8 Jun 2021 14:01:19 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Hao Xu <haoxu@...ux.alibaba.com>
Cc:     syzbot <syzbot+ea2f1484cffe5109dc10@...kaller.appspotmail.com>,
        Pavel Begunkov <asml.silence@...il.com>,
        Jens Axboe <axboe@...nel.dk>, io-uring@...r.kernel.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [syzbot] WARNING in io_wqe_enqueue

On Tue, Jun 8, 2021 at 11:47 AM Hao Xu <haoxu@...ux.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@...il.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@...kaller.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