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From: Jakub Sitnicki <jakub@cloudflare.com>
To: John Fastabend <john.fastabend@gmail.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
	bpf@vger.kernel.org, netdev@vger.kernel.org,
	kernel-team@cloudflare.com, Lorenz Bauer <lmb@cloudflare.com>,
	Martin Lau <kafai@fb.com>
Subject: Re: [PATCH bpf-next v4 02/12] net, sk_msg: Annotate lockless access to sk_prot on clone
Date: Mon, 27 Jan 2020 10:36:32 +0100	[thread overview]
Message-ID: <87k15dckbj.fsf@cloudflare.com> (raw)
In-Reply-To: <5e29f0caaec93_5aac2ad03f6d65c09b@john-XPS-13-9370.notmuch>

On Thu, Jan 23, 2020 at 08:15 PM CET, John Fastabend wrote:
> Jakub Sitnicki wrote:
>> On Thu, Jan 23, 2020 at 06:18 PM CET, Eric Dumazet wrote:
>> > On 1/23/20 7:55 AM, Jakub Sitnicki wrote:
>> >> sk_msg and ULP frameworks override protocol callbacks pointer in
>> >> sk->sk_prot, while tcp accesses it locklessly when cloning the listening
>> >> socket, that is with neither sk_lock nor sk_callback_lock held.
>> >>
>> >> Once we enable use of listening sockets with sockmap (and hence sk_msg),
>> >> there will be shared access to sk->sk_prot if socket is getting cloned
>> >> while being inserted/deleted to/from the sockmap from another CPU:
>
> [...]
>
>> >>  include/linux/skmsg.h | 3 ++-
>> >>  net/core/sock.c       | 5 +++--
>> >>  net/ipv4/tcp_bpf.c    | 4 +++-
>> >>  net/ipv4/tcp_ulp.c    | 3 ++-
>> >>  net/tls/tls_main.c    | 3 ++-
>> >>  5 files changed, 12 insertions(+), 6 deletions(-)
>> >>
>> >> diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
>> >> index 41ea1258d15e..55c834a5c25e 100644
>> >> --- a/include/linux/skmsg.h
>> >> +++ b/include/linux/skmsg.h
>> >> @@ -352,7 +352,8 @@ static inline void sk_psock_update_proto(struct sock *sk,
>> >>  	psock->saved_write_space = sk->sk_write_space;
>> >>
>> >>  	psock->sk_proto = sk->sk_prot;
>> >> -	sk->sk_prot = ops;
>> >> +	/* Pairs with lockless read in sk_clone_lock() */
>> >> +	WRITE_ONCE(sk->sk_prot, ops);
>> >
>> >
>> > Note there are dozens of calls like
>> >
>> > if (sk->sk_prot->handler)
>> >     sk->sk_prot->handler(...);
>> >
>> > Some of them being done lockless.
>> >
>> > I know it is painful, but presumably we need
>
> Correct.
>
>> >
>> > const struct proto *ops = READ_ONCE(sk->sk_prot);
>> >
>> > if (ops->handler)
>> >     ops->handler(....);

[...]

>>
>> Considering these are lacking today, can I do it as a follow up?
>
> In my opinion yes. I think pulling your patches in is OK and I started
> doing this conversion already so we can have a fix shortly. I didn't
> want to push it into rc7 though so I'll push it next week or into
> net-next tree.

Thanks, John. I'll take a look if there is any access to sk_prot, apart
from the clone path, applicable only to TCP listening sockets that needs
annotating.

  reply	other threads:[~2020-01-27  9:36 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-23 15:55 [PATCH bpf-next v4 00/12] Extend SOCKMAP to store listening sockets Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 01/12] bpf, sk_msg: Don't clear saved sock proto on restore Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 02/12] net, sk_msg: Annotate lockless access to sk_prot on clone Jakub Sitnicki
2020-01-23 17:18   ` Eric Dumazet
2020-01-23 18:56     ` Jakub Sitnicki
2020-01-23 19:15       ` John Fastabend
2020-01-27  9:36         ` Jakub Sitnicki [this message]
2020-01-23 15:55 ` [PATCH bpf-next v4 03/12] net, sk_msg: Clear sk_user_data pointer on clone if tagged Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 04/12] tcp_bpf: Don't let child socket inherit parent protocol ops on copy Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 05/12] bpf, sockmap: Allow inserting listening TCP sockets into sockmap Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 06/12] bpf, sockmap: Don't set up sockmap progs for listening sockets Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 07/12] bpf, sockmap: Return socket cookie on lookup from syscall Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 08/12] bpf, sockmap: Let all kernel-land lookup values in SOCKMAP Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 09/12] bpf: Allow selecting reuseport socket from a SOCKMAP Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 10/12] net: Generate reuseport group ID on group creation Jakub Sitnicki
2020-01-23 17:02   ` Martin Lau
2020-01-23 15:55 ` [PATCH bpf-next v4 11/12] selftests/bpf: Extend SK_REUSEPORT tests to cover SOCKMAP Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 12/12] selftests/bpf: Tests for SOCKMAP holding listening sockets Jakub Sitnicki
2020-01-27 11:13 ` [PATCH bpf-next v4 00/12] Extend SOCKMAP to store " Daniel Borkmann
2020-01-27 13:03   ` Jakub Sitnicki

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