linux-kernel - Re: INFO: rcu detected stall in sys

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CACT4Y+atEoMK8GFHTyH-L617-Qbsds5OkqcU1ibc2NR7DUKK3Q@mail.gmail.com>
Date:   Tue, 12 Mar 2019 18:10:37 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     syzbot <syzbot+1505c80c74256c6118a5@...kaller.appspotmail.com>,
        David Airlie <airlied@...ux.ie>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Amir Goldstein <amir73il@...il.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Dave Chinner <david@...morbit.com>,
        DRI <dri-devel@...ts.freedesktop.org>, eparis@...hat.com,
        Johannes Weiner <hannes@...xchg.org>,
        Hugh Dickins <hughd@...gle.com>,
        intel-gfx <intel-gfx@...ts.freedesktop.org>,
        Jan Kara <jack@...e.cz>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Souptick Joarder <jrdr.linux@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, Ingo Molnar <mingo@...hat.com>,
        mszeredi@...hat.com,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Peter Zijlstra <peterz@...radead.org>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: INFO: rcu detected stall in sys_sendfile64 (2)

On Tue, Mar 12, 2019 at 5:08 AM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> On Mon, Mar 11, 2019 at 08:59:00PM -0700, syzbot wrote:
> > syzbot has bisected this bug to:
> >
> > commit 34e07e42c55aeaa78e93b057a6664e2ecde3fadb
> > Author: Chris Wilson <chris@...is-wilson.co.uk>
> > Date:   Thu Feb 8 10:54:48 2018 +0000
> >
> >     drm/i915: Add missing kerneldoc for 'ent' in i915_driver_init_early
> >
> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=13220283200000
> > start commit:   34e07e42 drm/i915: Add missing kerneldoc for 'ent' in i915..
> > git tree:       upstream
> > final crash:    https://syzkaller.appspot.com/x/report.txt?x=10a20283200000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=17220283200000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=abc3dc9b7a900258
> > dashboard link: https://syzkaller.appspot.com/bug?extid=1505c80c74256c6118a5
> > userspace arch: amd64
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12c4dc28c00000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15df4108c00000
> >
> > Reported-by: syzbot+1505c80c74256c6118a5@...kaller.appspotmail.com
> > Fixes: 34e07e42 ("drm/i915: Add missing kerneldoc for 'ent' in
> > i915_driver_init_early")
>
> Umm...  Might be a good idea to add some plausibility filters - it is,
> in theory, possible that adding a line in a comment changes behaviour
> (without compiler bugs, even - playing with __LINE__ is all it would
> take), but the odds that it's _not_ a false positive are very low.

Thanks for pointing this out.

I've started collecting all such cases, so that we are able to draw
broader conclusions later:
https://github.com/google/syzkaller/issues/1051

added for this one:
=========
A mix of problems: unrelated bug triggered by the same repro
("WARNING: ODEBUG bug in netdev_freemem"); lots of infrastructure
failures ("failed to copy test binary to VM"); also the original
failure seems to be flaky. All this contributed to pointing to a
random commit.
Al Viro points out that the commit only touches comments, so we could
mark the end result as suspicious.
=========

The infrastructure problems is definitely something we need to fix
("failed to copy test binary to VM") (currently the machine hangs
periodically with lots of time consumed by dmcrypt, but I don't know
if it's related or not yet).

Re the comment-only changes, I would like to see more cases where it
would help before we start creating new universes for this. We could
parse sources with clang to understand that a change was comment-only,
but I guess kernel is mostly broken with clang throughout history....