Re: [PATCH net] ipv4/ipv6: preserve multicast filters after a failed source leave

[Xia Yan]

Hi,

The Sashiko review of this patch has two open Medium concerns [1].
Both describe behavior this patch does not change. My reading of each:

1) Empty-filter mode switch before the allocation in ip_mc_source() and
   ip6_mc_source().

   The mode-switch block is untouched. The diff only moves the sflist
   dereference up and returns early when no source list exists for a
   deletion. Add requests still reach the block in the original order,
   so a mode switch followed by a failed allocation is preexisting
   behavior. Restructuring that path would grow this stable-targeted
   fix well beyond the bug it addresses. I'm happy to look at it as
   follow-up work if there is interest.

2) IPv4 leaves a non-NULL, empty sflist after unblock, while IPv6 frees
   it.

   This patch changes neither when a source list is freed nor when it
   is kept. For a non-NULL empty list the new early check is a no-op:
   the delete path already tested !psl further down, and the mode check
   keyed on pmc->sflist before this change. The asymmetry predates the
   patch. Unifying it would alter observable behavior on a long-stable
   path, so it looks like a separate discussion to me.

No respin planned for these two. I will follow up if a maintainer
sees them differently.

[1] https://sashiko.dev/#/patchset/98602

Best regards,
Xia Yan