linux-kernel - Re: [PATCH] bpf, sockmap: defer sk_psock_free

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Date: Wed, 22 May 2024 06:59:18 +0800
From: Hillf Danton <hdanton@...a.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Eric Dumazet <edumazet@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	bpf <bpf@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] bpf, sockmap: defer sk_psock_free_link() using RCU

On Tue, 21 May 2024 08:38:52 -0700 Alexei Starovoitov <alexei.starovoitov@...il.com>
> On Sun, May 12, 2024 at 12:22=E2=80=AFAM Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp> wrote:
> > --- a/net/core/sock_map.c
> > +++ b/net/core/sock_map.c
> > @@ -142,6 +142,7 @@ static void sock_map_del_link(struct sock *sk,
> >         bool strp_stop =3D false, verdict_stop =3D false;
> >         struct sk_psock_link *link, *tmp;
> >
> > +       rcu_read_lock();
> >         spin_lock_bh(&psock->link_lock);
> 
> I think this is incorrect.
> spin_lock_bh may sleep in RT and it won't be safe to do in rcu cs.

Could you specify why it won't be safe in rcu cs if you are right?
What does rcu look like in RT if not nothing?
> 
> pw-bot: cr