[MPTCP] [RFC PATCH 0/2] mptcp: cope better with tcp_sendpage allocation

[Paolo Abeni <pabeni at redhat.com>]

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The current export branch suffers of the following issue:

https://github.com/multipath-tcp/mptcp_net-next/issues/97

To fix the above, MPTCP needs to be able to cope with memory allocation
failure in do_tcp_sendpages().

In this attempt, the relevant code is factored out of do_tcp_sendpages(),
in a smaller helper, so that mptcp_sendmsg_frag() can avoid touching
ssk->sk_socket.

There are other possible alternatives:
- add an explicit check in do_tcp_sendpages() for NULL sk->sk_socket
  pro: very simple and little invasive
  cons: hackysh?!?
- inline/open-code the relevant part of do_tcp_sendpages in mptcp_sendmsg_frag()
  pro: no need to change core TCP code
  cons: code duplication, need to change the scope for a couple of TCP internal
        helpers (removing the 'static' keyword)

As a follow-up I would try to pre-allocate skbs and extensions, so that
push_pending could be called in BH context and we could avoid using the 
work queue.

I'm looking for feedback on the less ugly/more upstreamable approach 

Paolo Abeni (2):
  tcp: factor out do_tcp_sendfrag()
  mptcp: use do_tcp_sendfrag()

 include/net/tcp.h    |   3 ++
 net/ipv4/tcp.c       | 120 ++++++++++++++++++++++++-------------------
 net/mptcp/protocol.c |  21 ++++----
 3 files changed, 80 insertions(+), 64 deletions(-)

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