linux-kernel - Re: [PATCH bpf v2 3/4] bpf, sockmap: Adapt for the af

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Message-ID: <c4eaead1-ad69-42f0-9699-5f2d555a7693@rbox.co>
Date: Sun, 8 Feb 2026 18:14:02 +0100
From: Michal Luczaj <mhal@...x.co>
To: Kuniyuki Iwashima <kuniyu@...gle.com>
Cc: John Fastabend <john.fastabend@...il.com>,
 Jakub Sitnicki <jakub@...udflare.com>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Simon Horman <horms@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Willem de Bruijn <willemb@...gle.com>, Cong Wang <cong.wang@...edance.com>,
 Alexei Starovoitov <ast@...nel.org>, Yonghong Song <yhs@...com>,
 Andrii Nakryiko <andrii@...nel.org>, Eduard Zingerman <eddyz87@...il.com>,
 Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
 Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Shuah Khan <shuah@...nel.org>,
 netdev@...r.kernel.org, bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf v2 3/4] bpf, sockmap: Adapt for the af_unix-specific
 lock

On 2/7/26 23:00, Kuniyuki Iwashima wrote:
> On Sat, Feb 7, 2026 at 6:35 AM Michal Luczaj <mhal@...x.co> wrote:
>> This patch also happens to fix a deadlock that may occur when
>> bpf_iter_unix_seq_show()'s lock_sock_fast() takes the fast path and the
>> iter prog attempts to update a sockmap. Which ends up spinning at
>> sock_map_update_elem()'s bh_lock_sock():
> 
> Hmm.. this seems to be a more general problem for
> bpf iter vs sockmap.  bpf_iter_{tcp,udp}_seq_show() also
> hold lock_sock(),  where this patch's solution does not help.
> We need to resolve this regardless of socket family.

I don't see any deadlocks there. Note that I've mentioned lock_sock_fast()
fast path was a problem, not lock_sock().

> Also, I feel lock_sock() should be outside of unix_state_lock()
> since the former is usually sleepable.  If we used such locking
> order in the future, it would trigger ABBA deadlock and we would
> have to revisit this problem.

Do I understand correctly you're suggesting taking lock_sock() for af_unix
just as well?