Re: possible deadlock in userfaultfd_release

[syzbot]

syzbot has bisected this bug to:

commit bfe4037e722ec672c9dafd5730d9132afeeb76e9
Author: Christoph Hellwig <hch@xxxxxx>
Date:   Mon Jul 16 07:08:20 2018 +0000

    aio: implement IOCB_CMD_POLL

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1382985d200000
start commit:   bfe4037e aio: implement IOCB_CMD_POLL
git tree:       upstream
final crash:    https://syzkaller.appspot.com/x/report.txt?x=1042985d200000
console output: https://syzkaller.appspot.com/x/log.txt?x=1782985d200000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5c0a49d2b5210087
dashboard link: https://syzkaller.appspot.com/bug?extid=53c0b767f7ca0dc0c451
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1111f2eb400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13e874f5400000

Reported-by: syzbot+53c0b767f7ca0dc0c451@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: bfe4037e722e ("aio: implement IOCB_CMD_POLL")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection