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

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Date:   Mon, 15 Jan 2018 15:00:39 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     syzbot 
        <bot+980f5e5fc060c37505bd65abb49a963518b269d9@...kaller.appspotmail.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>, jlayton@...hat.com,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Ingo Molnar <mingo@...nel.org>, npiggin@...il.com,
        rgoldwyn@...e.com, syzkaller-bugs@...glegroups.com,
        Jens Axboe <axboe@...nel.dk>, Ming Lei <tom.leiming@...il.com>,
        Hannes Reinecke <hare@...e.de>, Omar Sandoval <osandov@...com>,
        shli@...com
Subject: Re: INFO: task hung in filemap_fault

On Mon, Jan 15, 2018 at 2:56 PM, Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
> Dmitry Vyukov wrote:
>> > No problem. In the "tty: User triggerable soft lockup." case, I manually
>> > trimmed the reproducer at https://marc.info/?l=linux-mm&m=151368630414963 .
>> > That is,
>> >
>> >  (1) Can the problem be reproduced even if setup_tun(0, true); is commented out?
>> >
>> >  (2) Can the problem be reproduced even if NONFAILING(A = B); is replaced with
>> >      plain A = B; assignment?
>> >
>> >  (3) Can the problem be reproduced even if install_segv_handler(); is commented
>> >      out?
>> >
>> >  (4) Can the problem be reproduced even if some syscalls (e.g. __NR_memfd_create,
>> >      __NR_getsockopt, __NR_perf_event_open) are replaced with no-op?
>> >
>> > and so on. Then, I finally reached a reproducer which I sent, and the bug was fixed.
>> >
>> > What is important is that everyone can try simplifying the reproducer written
>> > in plain C in order to narrow down the culprit. Providing a (e.g.) CGI service
>> > which generates plain C reproducer like gistfile1.txt will be helpful to me.
>>
>> I am not completely following. You previously mentioned raw.log, which
>> is a collection of multiple programs, but now you seem to be talking
>> about a single reproducer. When syzbot manages to reproduce the bug
>> only with syzkaller program but not with a corresponding C program, it
>> provides only syzkaller program. It such case it can sense to convert.
>> But the case you pointed to actually contains C program. So there is
>> no need to do the conversion at all... What am I missing?
>>
>
> raw.log is not readable for me.
> I want to see C program even if syzbot did not manage to reproduce the bug.
> If C program is available, everyone can try reproducing the bug with manually
> trimmed C program.

If it did not manage to reproduce the bug, there is no C program.
There is no program at all.