Re: INFO: rcu detected stall in sys_sendfile64 (2)

[Jani Nikula]

On Tue, 12 Mar 2019, Al Viro <viro@xxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx>
>> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
>> 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