Re: INFO: task hung in filemap_fault

From: Dmitry Vyukov <dvyukov@google.com>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: syzbot
	<bot+980f5e5fc060c37505bd65abb49a963518b269d9@syzkaller.appspotmail.com>,
	Andi Kleen <ak@linux.intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jan Kara <jack@suse.cz>,
	jlayton@redhat.com, LKML <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	Ingo Molnar <mingo@kernel.org>,
	npiggin@gmail.com, rgoldwyn@suse.com,
	syzkaller-bugs@googlegroups.com, Jens Axboe <axboe@kernel.dk>,
	Ming Lei <tom.leiming@gmail.com>, Hannes Reinecke <hare@suse.de>,
	Omar Sandoval <osandov@fb.com>,
	shli@fb.com
Subject: Re: INFO: task hung in filemap_fault
Date: Mon, 15 Jan 2018 15:00:39 +0100	[thread overview]
Message-ID: <CACT4Y+Z2d6aV86rj5OYiv5Xw=D9xi=vW7RpdzP2X+vTnUjFqfQ@mail.gmail.com> (raw)
In-Reply-To: <201801152256.HDH17623.tSJHFLFOFMVOQO@I-love.SAKURA.ne.jp>

On Mon, Jan 15, 2018 at 2:56 PM, Tetsuo Handa
<penguin-kernel@i-love.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.

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