linux-kernel - Re: INFO: task hung in do_read_cache

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Date:   Tue, 12 May 2020 12:15:09 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Mike Christie <mchristi@...hat.com>
Cc:     syzbot <syzbot+518c54e255b5031adde4@...kaller.appspotmail.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Amir Goldstein <amir73il@...il.com>,
        Jens Axboe <axboe@...nel.dk>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Jan Kara <jack@...e.cz>, Josef Bacik <josef@...icpanda.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        william.kucharski@...cle.com, Matthew Wilcox <willy@...radead.org>
Subject: Re: INFO: task hung in do_read_cache_page (3)

On Mon, May 11, 2020 at 7:31 PM Mike Christie <mchristi@...hat.com> wrote:
>
> On 5/11/20 8:19 AM, syzbot wrote:
> > syzbot has bisected this bug to:
> >
> > commit 2da22da573481cc4837e246d0eee4d518b3f715e
> > Author: Mike Christie <mchristi@...hat.com>
> > Date:   Tue Aug 13 16:39:52 2019 +0000
> >
> >     nbd: fix zero cmd timeout handling v2
> >
> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11d6ab14100000
> > start commit:   e99332e7 gcc-10: mark more functions __init to avoid secti..
> > git tree:       upstream
> > final crash:    https://syzkaller.appspot.com/x/report.txt?x=13d6ab14100000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=15d6ab14100000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=8a96cf498e199d8b
> > dashboard link: https://syzkaller.appspot.com/bug?extid=518c54e255b5031adde4
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=146e45ec100000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=164444a4100000
> >
> > Reported-by: syzbot+518c54e255b5031adde4@...kaller.appspotmail.com
> > Fixes: 2da22da57348 ("nbd: fix zero cmd timeout handling v2")
> >
> > For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> >
>
> How do you adjust/modify what is expected from the test or what is
> reported as an error?
>
> The patch added back behavior that got removed. With the patch we expect
> the hung task warnings, because we specifically want to hold onto
> running commands for longer than 120/hung_task_timeout seconds

Hi Mike,

All task hung messages are considered a kernel bug. So far this was
always true as far as I can tell. Tasks that are blocked for any
prolonged period should be killable.