WARNING: ODEBUG bug in get_signal

[syzbot]

syzbot has bisected this issue to:

commit a9ed4a6560b8562b7e2e2bed9527e88001f7b682
Author: Marc Zyngier <maz at kernel.org>
Date:   Wed Aug 19 16:12:17 2020 +0000

    epoll: Keep a reference on files added to the check list

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=15e57751900000
start commit:   15bc20c6 Merge tag 'tty-5.9-rc3' of git://git.kernel.org/p..
git tree:       upstream
final oops:     https://syzkaller.appspot.com/x/report.txt?x=17e57751900000
console output: https://syzkaller.appspot.com/x/log.txt?x=13e57751900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=978db74cb30aa994
dashboard link: https://syzkaller.appspot.com/bug?extid=e3cf8f93cf86936710db
userspace arch: i386
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13236eb6900000

Reported-by: syzbot+e3cf8f93cf86936710db at syzkaller.appspotmail.com
Fixes: a9ed4a6560b8 ("epoll: Keep a reference on files added to the check list")

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