Re: FAILED: patch "[PATCH] mptcp: fix duplicate subflow creation" failed to apply to 5.15-stable tree

Hi Greg,

On 26/02/2024 14:18, gregkh@linuxfoundation.org wrote:

The patch below does not apply to the 5.15-stable tree.

(...)

Possible dependencies:

045e9d812868 ("mptcp: fix duplicate subflow creation")
b9d69db87fb7 ("mptcp: let the in-kernel PM use mixed IPv4 and IPv6 addresses")
bedee0b56113 ("mptcp: address lookup improvements")
4638de5aefe5 ("mptcp: handle local addrs announced by userspace PMs")
c682bf536cf4 ("mptcp: add pm_nl_pernet helpers")
4cf86ae84c71 ("mptcp: strict local address ID selection")
d045b9eb95a9 ("mptcp: introduce implicit endpoints")
aaa25a2fa796 ("Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net")

(...)

From 045e9d812868a2d80b7a57b224ce8009444b7bbc Mon Sep 17 00:00:00 2001
From: Paolo Abeni <pabeni@redhat.com>
Date: Thu, 15 Feb 2024 19:25:33 +0100
Subject: [PATCH] mptcp: fix duplicate subflow creation

Fullmesh endpoints could end-up unexpectedly generating duplicate
subflows - same local and remote addresses - when multiple incoming
ADD_ADDR are processed before the PM creates the subflow for the local
endpoints.

Address the issue explicitly checking for duplicates at subflow
creation time.

To avoid a quadratic computational complexity, track the unavailable
remote address ids in a temporary bitmap and initialize such bitmap
with the remote ids of all the existing subflows matching the local
address currently processed.

The above allows additionally replacing the existing code checking
for duplicate entry in the current set with a simple bit test
operation.

FYI, because of the various conflicts, and because the issue is quite
harmless -- duplicated subflows are created, but only when trying to
create a high number of subflows, limited to 8 in v5.15, almost
unnoticed bug so far --, I think it is better not to try to backport
this patch to v5.15.

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.