* Re: INFO: rcu detected stall in sys_sendfile64 (2)
2019-03-12 4:08 ` Al Viro
@ 2019-03-12 8:00 ` Jani Nikula
2019-03-12 17:10 ` Dmitry Vyukov
1 sibling, 0 replies; 4+ messages in thread
From: Jani Nikula @ 2019-03-12 8:00 UTC (permalink / raw)
To: Al Viro, syzbot
Cc: jack, penguin-kernel, david, dri-devel, linux-mm, darrick.wong,
hughd, willy, airlied, mingo, mszeredi, amir73il, intel-gfx,
syzkaller-bugs, rodrigo.vivi, dvyukov, linux-kernel, eparis,
peterz, jrdr.linux, hannes, akpm
On Tue, 12 Mar 2019, Al Viro <viro@zeniv.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@chris-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@syzkaller.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.
If it's not a false positive, it's bound to be good source material for
IOCCC.
BR,
Jani.
--
Jani Nikula, Intel Open Source Graphics Center
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^ permalink raw reply [flat|nested] 4+ messages in thread* Re: INFO: rcu detected stall in sys_sendfile64 (2)
2019-03-12 4:08 ` Al Viro
2019-03-12 8:00 ` Jani Nikula
@ 2019-03-12 17:10 ` Dmitry Vyukov
1 sibling, 0 replies; 4+ messages in thread
From: Dmitry Vyukov @ 2019-03-12 17:10 UTC (permalink / raw)
To: Al Viro
Cc: syzbot, David Airlie, Andrew Morton, Amir Goldstein, Chris Wilson,
Darrick J. Wong, Dave Chinner, DRI, eparis, Johannes Weiner,
Hugh Dickins, intel-gfx, Jan Kara, Jani Nikula, Joonas Lahtinen,
Souptick Joarder, LKML, Linux-MM, Ingo Molnar, mszeredi
On Tue, Mar 12, 2019 at 5:08 AM Al Viro <viro@zeniv.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@chris-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@syzkaller.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....
^ permalink raw reply [flat|nested] 4+ messages in thread