[syzbot] kernel BUG in rxrpc_put_peer

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+c22650d2844392afdcfd at syzkaller.appspotmail.com

Tested on:

commit:         efb7555b rxrpc: Fix I/O thread stop
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/ afs-testing
console output: https://syzkaller.appspot.com/x/log.txt?x=13660d6b880000
kernel config:  https://syzkaller.appspot.com/x/.config?x=331c73ac8d6e1cab
dashboard link: https://syzkaller.appspot.com/bug?extid=c22650d2844392afdcfd
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

Note: no patches were applied.
Note: testing is done by a robot and is best-effort only.