Subject: Re: [PATCH] bpf, sockmap: fix deadlock in rcu_report_exp_cpu_mult

From: Jakub Sitnicki <[email-masked]>
Date: Mon, 25 Mar 2024 14:49:19 +0100

On Mon, Mar 25, 2024 at 01:23 PM +01, Jakub Sitnicki wrote:

[...]

> But we also need to cover sock_map_unref->sock_sock_map_del_link called
> from sock_hash_delete_elem. It also grabs a spin lock.

On second look, no need to disable interrupts in
sock_map_unref->sock_sock_map_del_link. Call is enclosed in the critical
section in sock_hash_delete_elem that has been updated.

I have a question, though, why are we patching sock_hash_free? It
doesn't get called unless there are no more existing users of the BPF
map. So nothing can mutate it from interrupt context.

[...]