[MPTCP] Re: [PATCH mptcp-next 3/7] mptcp: avoid blocking in tcp_sendpages due to skb alloc

[Florian Westphal <fw at strlen.de>]

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Paolo Abeni <pabeni(a)redhat.com> wrote:
> Ok, I missed/forgot that the retransmission must be non blocking.
> 
> I now see that retransmissions are fine as is!
> 
> Still on this, don't we need to check mptcp_sendmsg_alloc_skb() inside
> the sendmsg() loop, too? Elsewhere we could fail on large send if we
> complete the first skb, keep looping in sendmsg() and the next
> iteration would block. Am I missing something?

You mean:

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 780d873b6c19..66a67b11d01b 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -814,6 +814,7 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
                if (!tx_ok)
                        break;
                if (!sk_stream_memory_free(ssk) ||
+                   !mptcp_sendmsg_alloc_skb(ssk) ||
                    !mptcp_page_frag_refill(ssk, pfrag) ||
                    !mptcp_ext_cache_refill(msk)) {
                        tcp_push(ssk, msg->msg_flags, mss_now,

?

Yes, that could be added.  Its not a huge deal since mptcp_sendmsg_frag() would
yield -EAGAIN if do_tcp_sendpages would block, and that will then re-start for
the 'blocking io' case (i.e., ssk is released and 'goto restart' fetches next
ssk with posssible wait_for_memory).