Subject: deadlocks on pernet_ops_rwsem

From: Jakub Kicinski <[email-masked]>
Date: Wed, 1 Oct 2025 08:20:36 -0700

Hi!

We started hitting a deadlock on pernet_ops_rwsem, not very often,
these are the CI branches were we saw it:

 2025-09-18--03-00
 2025-09-18--15-00
 2025-09-18--18-00
 2025-09-19--21-00
 2025-09-21--15-00
 2025-09-21--18-00
 2025-09-22--00-00
 2025-09-22--09-00
 2025-09-23--06-00
 2025-09-24--21-00
 2025-09-27--21-00
 2025-09-28--09-00
 2025-10-01--00-00
 2025-10-01--06-00

First hit seems to be:
https://netdev-3.bots.linux.dev/vmksft-net-dbg/results/302741/65-l2tp-sh/stderr
Two most recent:
https://netdev-3.bots.linux.dev/vmksft-net-dbg/results/321640/110-ip-local-port-range-sh/stderr
https://netdev-3.bots.linux.dev/vmksft-net-dbg/results/321281/63-fdb-notify-sh/stderr

The stack traces aren't very helpful, they mostly show the victim not
who caused the deadlock :(

Any ideas?