INFO: rcu detected stall in sys_sendfile64 (2)

[Al Viro]

On Mon, Mar 11, 2019 at 08:59:00PM -0700, syzbot wrote:
> syzbot has bisected this bug to:
> 
> commit 34e07e42c55aeaa78e93b057a6664e2ecde3fadb
> Author: Chris Wilson <chris at 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 at 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.