Subject: Re: [bpf PATCH 3/9] bpf: sockmap/tls, push write_space updates through ulp updates

From: Jakub Sitnicki <[email-masked]>
Date: Fri, 10 Jan 2020 14:40:20 +0100

On Thu, Jan 09, 2020 at 10:22 PM CET, John Fastabend wrote:
> Jakub Sitnicki wrote:
>> On Wed, Jan 08, 2020 at 10:14 PM CET, John Fastabend wrote:
>> > When sockmap sock with TLS enabled is removed we cleanup bpf/psock state
>> > and call tcp_update_ulp() to push updates to TLS ULP on top. However, we
>> > don't push the write_space callback up and instead simply overwrite the
>> > op with the psock stored previous op. This may or may not be correct so
>> > to ensure we don't overwrite the TLS write space hook pass this field to
>> > the ULP and have it fixup the ctx.
>> >
>> > This completes a previous fix that pushed the ops through to the ULP
>> > but at the time missed doing this for write_space, presumably because
>> > write_space TLS hook was added around the same time.
>> >
>> > Fixes: 95fa145479fbc ("bpf: sockmap/tls, close can race with map free")
>> > Signed-off-by: John Fastabend <[email-masked]>
>> > ---
>> >  include/linux/skmsg.h |   12 ++++++++----
>> >  include/net/tcp.h     |    6 ++++--
>> >  net/ipv4/tcp_ulp.c    |    6 ++++--
>> >  net/tls/tls_main.c    |   10 +++++++---
>> >  4 files changed, 23 insertions(+), 11 deletions(-)
>> >
>> > diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
>> > index b6afe01f8592..14d61bba0b79 100644
>> > --- a/include/linux/skmsg.h
>> > +++ b/include/linux/skmsg.h
>> > @@ -359,17 +359,21 @@ static inline void sk_psock_restore_proto(struct sock *sk,
>> >  					  struct sk_psock *psock)
>> >  {
>> >  	sk->sk_prot->unhash = psock->saved_unhash;
>> > -	sk->sk_write_space = psock->saved_write_space;
>> >
>> >  	if (psock->sk_proto) {
>> >  		struct inet_connection_sock *icsk = inet_csk(sk);
>> >  		bool has_ulp = !!icsk->icsk_ulp_data;
>> >
>> > -		if (has_ulp)
>> > -			tcp_update_ulp(sk, psock->sk_proto);
>> > -		else
>> > +		if (has_ulp) {
>> > +			tcp_update_ulp(sk, psock->sk_proto,
>> > +				       psock->saved_write_space);
>> > +		} else {
>> >  			sk->sk_prot = psock->sk_proto;
>> > +			sk->sk_write_space = psock->saved_write_space;
>> > +		}
>>
>> I'm wondering if we need the above fallback branch for no-ULP case?
>> tcp_update_ulp repeats the ULP check and has the same fallback. Perhaps
>> it can be reduced to:
>>
>> 	if (psock->sk_proto) {
>> 		tcp_update_ulp(sk, psock->sk_proto, psock->saved_write_space);
>> 		psock->sk_proto = NULL;
>> 	} else {
>> 		sk->sk_write_space = psock->saved_write_space;
>> 	}
>
> Yeah that is a bit nicer. How about pushing it for bpf-next? I'm not
> sure its needed for bpf and the patch I pushed is the minimal change
> needed for the fix and pushes the saved_write_space around.

Yeah, this is bpf-next material.

>> Then there's the question if it's okay to leave psock->sk_proto set and
>> potentially restore it more than once? Reading tls_update, the only user
>> ULP 'update' callback, it looks fine.
>>
>> Can sk_psock_restore_proto be as simple as:
>>
>> static inline void sk_psock_restore_proto(struct sock *sk,
>> 					  struct sk_psock *psock)
>> {
>> 	tcp_update_ulp(sk, psock->sk_proto, psock->saved_write_space);
>> }
>>
>> ... or am I missing something?
>
> I think that is good. bpf-next?

Great, I needed to confirm my thinking.

>> Asking becuase I have a patch [0] like this in the queue and haven't
>> seen issues with it during testing.
>
> +1 Want to push it after we sort out this series?

I've actually pushed it earlier today with next iteration of "Extend
SOCKMAP to store listening sockets" to collect feedback [0]. I will
adapt it once it shows up in bpf-next (or split it out and submit
separately).

-jkbs

[0] https://lore.kernel.org/bpf/[email-masked]/