[PATCH mptcp-next v2 00/10] mptcp: address stall under memory pressure

[Paolo Abeni <pabeni@redhat.com>]

This an attempt to fix the data transfer stall reported by Geliang and
Gang more carefully enforcing memory constraints at the MPTCP level.

Patch 1/10 moves the bound check before entering the TCP socket.
Patch 2, 3, 4 and 5 are cleanups/refactors finalized to safely re-using
TCP helpers on MPTCP skbs.
Patch 6 makes TCP pruning related helpers available to MPTCP and patch 7
makes use of them. Patch 8 addresses an edge scenario that could still
lead to transfer stall under memory pressure.
Finally patch 9 and 10 improve the MPTCP-level retransmission schema to
make recovery from memory pressure significanly faster.

Note that the diffstat is biases by the quite large patch 4/9, which
contains mechanical transformation of existing code; "real" changes are
noticiable smaller.

Tested successfully vs the test cases proposed by Geliang and Gang and
vs the selftests.
---
Notes:
- Sashiko apparently can't understand that mptcp_data_lock() &&
sk not owned by the user-space is equivalent to the sk socket lock. As a
consequences marks incorrectly as racy a few accesses under the data
lock to the sk_rcvbuf.
- mptcp_join with "4 subflows with under pressure" may require longer
than default timeout, as the transfer in such condition can be really
slow.

Paolo Abeni (10):
  mptcp: move checks vs rcvbuf size earlier in the RX path
  mptcp: drop the mptcp_ooo_try_coalesce() helper
  mptcp: drop the cant_coalesce CB field
  mptcp: remove CB offset field
  mptcp: sync mptcp skb cb layout with tcp one
  tcp: expose the tcp_collapse_ofo_queue() helper to mptcp usage, too
  mptcp: implemented OoO queue pruning
  mptcp: track prune recovery status
  mptcp: move the retrans loop to a separate helper
  mptcp: let the retrans scheduler do its job.

 include/net/tcp.h    |   8 +
 net/ipv4/tcp_input.c |  55 +++---
 net/mptcp/fastopen.c |   9 +-
 net/mptcp/mib.c      |   3 +
 net/mptcp/mib.h      |   3 +
 net/mptcp/options.c  |  58 ++++++-
 net/mptcp/protocol.c | 403 ++++++++++++++++++++++++++++---------------
 net/mptcp/protocol.h |  18 +-
 net/mptcp/subflow.c  |  10 ++
 9 files changed, 398 insertions(+), 169 deletions(-)

-- 
2.53.0