linux-kernel - Re: BUG: unable to handle kernel paging request in io_wq_cancel

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Date:   Fri, 1 Nov 2019 18:50:05 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     syzbot <syzbot+221cc24572a2fed23b6b@...kaller.appspotmail.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        David Howells <dhowells@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        linux-block <linux-block@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, mchehab+samsung@...nel.org,
        Ingo Molnar <mingo@...hat.com>, patrick.bellasi@....com,
        Richard Guy Briggs <rgb@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Subject: Re: BUG: unable to handle kernel paging request in io_wq_cancel_all

On Wed, Oct 30, 2019 at 3:41 PM Jens Axboe <axboe@...nel.dk> wrote:
>
> On 10/30/19 1:44 AM, syzbot wrote:
> > syzbot has bisected this bug to:
> >
> > commit ef0524d3654628ead811f328af0a4a2953a8310f
> > Author: Jens Axboe <axboe@...nel.dk>
> > Date:   Thu Oct 24 13:25:42 2019 +0000
> >
> >       io_uring: replace workqueue usage with io-wq
> >
> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=16acf5d0e00000
> > start commit:   c57cf383 Add linux-next specific files for 20191029
> > git tree:       linux-next
> > final crash:    https://syzkaller.appspot.com/x/report.txt?x=15acf5d0e00000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=11acf5d0e00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=cb86688f30db053d
> > dashboard link: https://syzkaller.appspot.com/bug?extid=221cc24572a2fed23b6b
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=168671d4e00000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=140f4898e00000
> >
> > Reported-by: syzbot+221cc24572a2fed23b6b@...kaller.appspotmail.com
> > Fixes: ef0524d36546 ("io_uring: replace workqueue usage with io-wq")
>
> Good catch, it's a case of NULL vs ERR_PTR() confusion. I'll fold in
> the below fix.

Hi Jens,

Please either add the syzbot tag to commit, or close manually with
"#syz fix" (though requires waiting until the fixed commit is in
linux-next).
See https://goo.gl/tpsmEJ#rebuilt-treesamended-patches for details.
Otherwise, the bug will be considered open and will waste time of
humans looking at open bugs and prevent syzbot from reporting new bugs
in io_uring.

> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index af1937d66aee..76d653085987 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -3534,8 +3534,9 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
>         /* Do QD, or 4 * CPUS, whatever is smallest */
>         concurrency = min(ctx->sq_entries, 4 * num_online_cpus());
>         ctx->io_wq = io_wq_create(concurrency, ctx->sqo_mm);
> -       if (!ctx->io_wq) {
> -               ret = -ENOMEM;
> +       if (IS_ERR(ctx->io_wq)) {
> +               ret = PTR_ERR(ctx->io_wq);
> +               ctx->io_wq = NULL;
>                 goto err;
>         }
>
>
> --
> Jens Axboe
>
> --
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