KASAN: use-after-free Read in afs_deactivate_cell (2)

[syzbot]

syzbot has bisected this issue to:

commit 13fcc6837049f1bd76d57e9abc217a91fdbad764
Author: David Howells <dhowells at redhat.com>
Date:   Thu Nov 1 23:07:27 2018 +0000

    afs: Add fs_context support

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=13ea9ea7900000
start commit:   49e7e3e9 Add linux-next specific files for 20200929
git tree:       linux-next
final oops:     https://syzkaller.appspot.com/x/report.txt?x=101a9ea7900000
console output: https://syzkaller.appspot.com/x/log.txt?x=17ea9ea7900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b823d07e241e7aee
dashboard link: https://syzkaller.appspot.com/bug?extid=a5e4946b04d6ca8fa5f3
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=173c446d900000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14ba5be3900000

Reported-by: syzbot+a5e4946b04d6ca8fa5f3 at syzkaller.appspotmail.com
Fixes: 13fcc6837049 ("afs: Add fs_context support")

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