Re: [PATCH v6 mptcp-next 00/11] mptcp: introduce backlog processing

[Geliang Tang <geliang@kernel.org>]

Hi Paolo,

Thanks for this v6.

On Wed, 2025-10-22 at 16:31 +0200, Paolo Abeni wrote:
> This series includes RX path improvement built around backlog
> processing
> 
> The main goals are improving the RX performances _and_ increase the
> long term maintainability.
> 
> Patches 2-4 prepare the stack for backlog processing, removing
> assumptions that will not hold true anymore after backlog
> introduction.
> 
> Patches 1 and 5 fixes long standing issues which are quite hard to
> reproduce with the current implementation but the 2nd one will become
> very apparent with backlog usage.
> 
> Patches 6, 7 and 9 are more cleanups that will make the backlog patch
> a
> little less huge.
> 
> Patch 8 is a somewhat unrelated cleanup, included here before I
> forgot
> about it.
> 
> The real work is done by patch 10 and 11. Patch 10 introduces the
> helpers
> needed to manipulate the msk-level backlog, and the data struct
> itself,
> without any actual functional change. Patch 11 finally use the
> backlog
> for RX skb processing. Note that MPTCP can't uset the sk_backlog, as
> the mptcp release callback can also release and re-acquire the msk-
> level
> spinlock and core backlog processing works under the assumption that
> such event is not possible.
> 
> A relevant point is memory accounts for skbs in the backlog.
> 
> It's somewhat "original" due to MPTCP constraints. Such skbs use
> space
> from the incoming subflow receive buffer, do not use explicitly any
> forward allocated memory, as we can't update the msk fwd mem while
> enqueuing, nor we want to acquire again the ssk socket lock while
> processing the skbs.
> 
> Instead the msk borrows memory from the subflow and reserve it for
> the backlog - see patch 3 and 11 for the gory details.
> 
> Note that even if the skbs can sit in the backlog for an unbounded
> time,
> 
> ---
> v5 -> v6:
>  - added patch 1/11
>  - reworked widely patch 10 && 11 to avoid double accounts for
> backlog
>    skb and to address the fwd allocated memory criticality mentioned
>    in previous iterations.

All tests have passed on my end. The only minor issues requiring
cleanup are in patch 2 and patch 9, which Matt or I can address in
subsequent revisions. All patches LGTM.

Reviewed-by: Geliang Tang <geliang@kernel.org>
Tested-by: Geliang Tang <geliang@kernel.org>

> 
> Paolo Abeni (11):
>   mptcp: drop bogus optimization in __mptcp_check_push()
>   mptcp: borrow forward memory from subflow
>   mptcp: cleanup fallback data fin reception
>   mptcp: cleanup fallback dummy mapping generation
>   mptcp: fix MSG_PEEK stream corruption
>   mptcp: ensure the kernel PM does not take action too late
>   mptcp: do not miss early first subflow close event notification.
>   mptcp: make mptcp_destroy_common() static
>   mptcp: drop the __mptcp_data_ready() helper
>   mptcp: introduce mptcp-level backlog
>   mptcp: leverage the backlog for RX packet processing
> 
>  net/mptcp/mptcp_diag.c |   3 +-
>  net/mptcp/pm.c         |   4 +-
>  net/mptcp/pm_kernel.c  |   2 +
>  net/mptcp/protocol.c   | 363 ++++++++++++++++++++++++++++-----------
> --
>  net/mptcp/protocol.h   |  10 +-
>  net/mptcp/subflow.c    |  12 +-
>  6 files changed, 272 insertions(+), 122 deletions(-)
>