Re: [PATCH 1/2] netlink: Use regular request/response netlink socket for initial neighbour sync

[Stefano Brivio <sbrivio@redhat.com>]

On Fri, 22 May 2026 10:02:27 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Thu, May 21, 2026 at 08:01:45PM +0200, Stefano Brivio wrote:
> > ...instead of the one dedicated to the neighbour monitor, because, if
> > neighbour notifications start coming in before or while we send the
> > initial request to read out the neighbour tables, messages and
> > sequence numbers will collide.
> > 
> > For example, if nl_neigh_sync() sends a RTM_GETNEIGH request with
> > sequence 20, we expect a corresponding reply with sequence 20. But
> > given that we already used the same socket to subscribe to
> > notifications, and notifications don't correspond to any specific
> > request we sent, we might now get a message with sequence 0.  
> 
> Heh.  Called it, kinda.  Nice job tracking this down.

Your suggestion that we were probably mixing up messages helped as a
starting point. Then I think we concluded that _of course_ it's
different sockets and they can't influence each other.

So I started looking into how two netlink sockets belonging to the same
process could possibly interfere with each other, until I tried to skip
the creation of nl_neigh_sock and realised that nl_neigh_sync() stopped
working altogether... oops.

-- 
Stefano