From: Dave Chinner <david@fromorbit.com>
To: Jan Kara <jack@suse.cz>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
syzbot <syzbot+4a7438e774b21ddd8eca@syzkaller.appspotmail.com>,
syzkaller-bugs@googlegroups.com, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk,
axboe@kernel.dk, tj@kernel.org, linux-block@vger.kernel.org,
Dmitry Vyukov <dvyukov@google.com>
Subject: Re: general protection fault in wb_workfn (2)
Date: Fri, 1 Jun 2018 12:30:02 +1000 [thread overview]
Message-ID: <20180601023002.GA10972@dastard> (raw)
In-Reply-To: <20180531134212.oo4ra4ypuruab3xp@quack2.suse.cz>
On Thu, May 31, 2018 at 03:42:12PM +0200, Jan Kara wrote:
> On Thu 31-05-18 22:19:44, Tetsuo Handa wrote:
> > On 2018/05/31 20:42, Jan Kara wrote:
> > > On Thu 31-05-18 01:00:08, Tetsuo Handa wrote:
> > >> So, we have no idea what is happening...
> > >> Then, what about starting from temporary debug printk() patch shown below?
> > >>
> > >> >From 4f70f72ad3c9ae6ce1678024ef740aca4958e5b0 Mon Sep 17 00:00:00 2001
> > >> From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > >> Date: Wed, 30 May 2018 09:57:10 +0900
> > >> Subject: [PATCH] bdi: Add temporary config for debugging wb_workfn() versus
> > >> bdi_unregister() race bug.
> > >>
> > >> syzbot is hitting NULL pointer dereference at wb_workfn() [1]. But due to
> > >> limitations that syzbot cannot find reproducer for this bug (frequency is
> > >> once or twice per a day) nor we can't capture vmcore in the environment
> > >> which syzbot is using, for now we need to rely on printk() debugging.
> > >>
> > >> [1] https://syzkaller.appspot.com/bug?id=e0818ccb7e46190b3f1038b0c794299208ed4206
> > >>
> > >> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > >
> > > Hum a bit ugly solution but if others are fine with this, I can live with
> > > it for a while as well. Or would it be possible for syzkaller to just test
> > > some git tree where this patch is included? Then we would not even have to
> > > have the extra config option...
> >
> > If syzbot can reproduce this bug that way. While it is possible to add/remove
> > git trees syzbot tests, frequently adding/removing trees is bothering.
> >
> > syzbot can enable extra config option. Maybe the config name should be
> > something like CONFIG_DEBUG_FOR_SYZBOT rather than individual topic.
> >
> > I think that syzbot is using many VM instances. I don't know how many
> > instances will be needed for reproducing this bug within reasonable period.
> > More git trees syzbot tests, (I assume that) longer period will be needed
> > for reproducing this bug. The most reliable way is to use the shared part
> > of all trees (i.e. linux.git).
>
> I understand this, I'd be just a bit reluctant to merge temporary debug
> patches like this to Linus' tree only to revert them later just because
> syzkaller... What do others think?
Don't commit temporary debug crap to the mainline kernel. Enable
syzkaller to run against a user supplied git tree specification if
it needs special debug to track down a problem.
-Dave.
--
Dave Chinner
david@fromorbit.com
prev parent reply other threads:[~2018-06-01 2:30 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-26 9:15 general protection fault in wb_workfn (2) syzbot
2018-05-27 0:47 ` Tetsuo Handa
2018-05-27 2:21 ` [PATCH] bdi: Fix another oops in wb_workfn() Tetsuo Handa
2018-05-27 2:36 ` Tejun Heo
2018-05-28 13:35 ` general protection fault in wb_workfn (2) Jan Kara
2018-05-30 16:00 ` Tetsuo Handa
2018-05-31 11:42 ` Jan Kara
2018-05-31 13:19 ` Tetsuo Handa
2018-05-31 13:42 ` Jan Kara
2018-05-31 16:56 ` Jens Axboe
2018-06-05 13:45 ` Tetsuo Handa
2018-06-07 18:46 ` Dmitry Vyukov
2018-06-08 2:31 ` Tetsuo Handa
2018-06-08 14:45 ` Dmitry Vyukov
2018-06-08 15:16 ` Dmitry Vyukov
2018-06-08 16:53 ` Dmitry Vyukov
2018-06-08 17:14 ` Dmitry Vyukov
2018-06-09 5:30 ` Tetsuo Handa
2018-06-09 14:00 ` [PATCH] bdi: Fix another oops in wb_workfn() Tetsuo Handa
2018-06-11 9:12 ` Jan Kara
2018-06-11 16:01 ` Tejun Heo
2018-06-11 16:29 ` Jan Kara
2018-06-11 17:20 ` Tejun Heo
2018-06-12 15:57 ` Jan Kara
2018-06-13 10:43 ` Tetsuo Handa
2018-06-13 11:51 ` Tetsuo Handa
2018-06-13 14:06 ` Linus Torvalds
2018-06-13 14:46 ` Jan Kara
2018-06-13 14:55 ` Linus Torvalds
2018-06-13 16:20 ` Tetsuo Handa
2018-06-13 16:25 ` Linus Torvalds
2018-06-13 16:45 ` Jan Kara
2018-06-13 21:04 ` Tetsuo Handa
2018-06-14 10:11 ` Jan Kara
2018-06-13 14:33 ` Tejun Heo
2018-06-15 12:06 ` Jan Kara
2018-06-18 12:27 ` Jan Kara
2018-06-01 2:30 ` Dave Chinner [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180601023002.GA10972@dastard \
--to=david@fromorbit.com \
--cc=axboe@kernel.dk \
--cc=dvyukov@google.com \
--cc=jack@suse.cz \
--cc=linux-block@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=penguin-kernel@i-love.sakura.ne.jp \
--cc=syzbot+4a7438e774b21ddd8eca@syzkaller.appspotmail.com \
--cc=syzkaller-bugs@googlegroups.com \
--cc=tj@kernel.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).