From: Jakub Sitnicki <jakub@cloudflare.com>
To: Hillf Danton <hdanton@sina.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
Eric Dumazet <edumazet@google.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
bpf <bpf@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] bpf, sockmap: defer sk_psock_free_link() using RCU
Date: Wed, 22 May 2024 11:50:49 +0200 [thread overview]
Message-ID: <877cfmxjie.fsf@cloudflare.com> (raw)
In-Reply-To: <20240521225918.2147-1-hdanton@sina.com> (Hillf Danton's message of "Wed, 22 May 2024 06:59:18 +0800")
On Wed, May 22, 2024 at 06:59 AM +08, Hillf Danton wrote:
> On Tue, 21 May 2024 08:38:52 -0700 Alexei Starovoitov <alexei.starovoitov@gmail.com>
>> On Sun, May 12, 2024 at 12:22=E2=80=AFAM Tetsuo Handa <penguin-kernel@i-love.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?
RCU readers can't block, while spinlock RT doesn't disable preemption.
https://docs.kernel.org/RCU/rcu.html
https://docs.kernel.org/locking/locktypes.html#spinlock-t-and-preempt-rt
I've finally gotten around to testing proposed fix that just disallows
map_delete_elem on sockmap/sockhash from BPF tracing progs
completely. This should put an end to this saga of syzkaller reports.
https://lore.kernel.org/all/87jzjnxaqf.fsf@cloudflare.com/
next prev parent reply other threads:[~2024-05-22 9:50 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-12 7:21 [PATCH] bpf, sockmap: defer sk_psock_free_link() using RCU Tetsuo Handa
2024-05-21 15:38 ` Alexei Starovoitov
2024-05-21 22:59 ` Hillf Danton
2024-05-22 9:50 ` Jakub Sitnicki [this message]
2024-05-22 10:30 ` Tetsuo Handa
2024-05-22 11:08 ` Jakub Sitnicki
2024-05-22 11:33 ` Hillf Danton
2024-05-22 12:12 ` Jakub Sitnicki
2024-05-22 14:57 ` Alexei Starovoitov
2024-05-24 13:06 ` Jakub Sitnicki
2024-05-27 11:22 ` Jakub Sitnicki
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