Re: [PATCH mptcp-next v2 2/3] mptcp: allow overridden write_space to be invoked

[Geliang Tang <geliang@kernel.org>]

Hi Matt,

On Wed, 2026-02-04 at 12:56 +0100, Matthieu Baerts wrote:
> Hi Geliang, Paolo,
> 
> On 04/01/2026 06:29, Geliang Tang wrote:
> > From: Geliang Tang <tanggeliang@kylinos.cn>
> > 
> > psock may override its own sk_write_space functions. This patch
> > ensures
> > that the overridden sk_write_space can be invoked by MPTCP.
> > 
> > Note: This patch was initially included in the NVME MPTCP set.
> > 
> > Suggested-by: Paolo Abeni <pabeni@redhat.com>
> > Co-developed-by: Gang Yan <yangang@kylinos.cn>
> > Signed-off-by: Gang Yan <yangang@kylinos.cn>
> > Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
> > ---
> >  net/mptcp/protocol.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
> > index cd5266099993..f5d4d7d030f2 100644
> > --- a/net/mptcp/protocol.h
> > +++ b/net/mptcp/protocol.h
> > @@ -1014,7 +1014,7 @@ static inline void mptcp_write_space(struct
> > sock *sk)
> >  	/* pairs with memory barrier in mptcp_poll */
> >  	smp_mb();
> >  	if (mptcp_stream_memory_free(sk, 1))
> > -		sk_stream_write_space(sk);
> > +		INDIRECT_CALL_1(sk->sk_write_space,
> > sk_stream_write_space, sk);
> 
> As I mentioned on the netdev ML when sending this patch upstream,

Sorry for the trouble.

> there
> is something fishy here: sk->sk_write_space is never set to
> sk_stream_write_space here with the MPTCP sockets, but to
> sock_def_write_space. (Subflow sockets use sk_stream_write_space.)
> 
> In other words, this patch changes the behaviour, which was not
> supposed
> to be the case, now calling sock_def_write_space() instead of
> sk_stream_write_space().
> 
> So either sk->sk_write_space should be set to sk_stream_write_space
> for
> the MPTCP sockets (I guess, I don't think sk->sk_write_space() is
> ever

I just sent a squash-to patch to set it to sk_stream_write_space for
the MPTCP sockets.

Thanks,
-Geliang

> called with an MPTCP socket for the moment), or
> sock_def_write_space()
> should have been called before (then a fix is needed).
> 
> Cheers,
> Matt