INFO: rcu detected stall in sys_sendfile64 (2)

[syzbot]

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")