Re: [PATCH 5.15.y] mptcp: consolidate fallback and non fallback state machine

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Jun 27, 2023 at 03:25:57PM +0200, Matthieu Baerts wrote:
> From: Paolo Abeni <pabeni@redhat.com>
> 
> commit 81c1d029016001f994ce1c46849c5e9900d8eab8 upstream.
> 
> An orphaned msk releases the used resources via the worker,
> when the latter first see the msk in CLOSED status.
> 
> If the msk status transitions to TCP_CLOSE in the release callback
> invoked by the worker's final release_sock(), such instance of the
> workqueue will not take any action.
> 
> Additionally the MPTCP code prevents scheduling the worker once the
> socket reaches the CLOSE status: such msk resources will be leaked.
> 
> The only code path that can trigger the above scenario is the
> __mptcp_check_send_data_fin() in fallback mode.
> 
> Address the issue removing the special handling of fallback socket
> in __mptcp_check_send_data_fin(), consolidating the state machine
> for fallback and non fallback socket.
> 
> Since non-fallback sockets do not send and do not receive data_fin,
> the mptcp code can update the msk internal status to match the next
> step in the SM every time data fin (ack) should be generated or
> received.
> 
> As a consequence we can remove a bunch of checks for fallback from
> the fastpath.
> 
> Fixes: 6e628cd3a8f7 ("mptcp: use mptcp release_cb for delayed tasks")
> Cc: stable@vger.kernel.org
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> Reviewed-by: Mat Martineau <martineau@kernel.org>
> Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
> ---
> Conflicting with:
> - 0522b424c4c2 ("mptcp: add do_check_data_fin to replace copied")
> - 3e5014909b56 ("mptcp: cleanup MPJ subflow list handling")
> 
> I took the new modifications but leaving the old variable name for
> "copied" instead of "do_check_data_fin" and the calls to
> __mptcp_flush_join_list()
> 
> Applied on top of d2efde0d1c2e ("Linux 5.15.119-rc1").
> 
> Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>

All backports now queued up, thanks.

greg k-h