Re: [PATCH 1/1] net: Add SO_REUSEPORT_LISTEN_OFF socket option as drain mode

[Eric Dumazet <eric.dumazet@gmail.com>]

On Fri, 2015-12-18 at 19:58 +0100, Willy Tarreau wrote:
> Hi Josh,
> 
> On Fri, Dec 18, 2015 at 08:33:45AM -0800, Josh Snyder wrote:
> > I was also puzzled that binding succeeded. Looking into the code paths
> > involved, in inet_csk_get_port, we quickly goto have_snum. From there, we end
> > up dropping into tb_found. Since !hlist_empty(&tb->owners), we end up checking
> > that (tb->fastreuseport > 0 && sk->sk_reuseport && uid_eq(tb->fastuid, uid)).
> > This test passes, so we goto success and bind.
> > 
> > Crucially, we are checking the fastreuseport field on the inet_bind_bucket, and
> > not the sk_reuseport variable on the other sockets in the bucket. Since this
> > bit is set based on sk_reuseport at the time the first socket binds (see
> > tb_not_found), I can see no reason why sockets need to keep SO_REUSEPORT set
> > beyond initial binding.
> > 
> > Given this, I believe Willy's patch elegantly solves the problem at hand.
> 
> Great, thanks for your in-depth explanation.
> 
> Eric, do you think that this patch may be acceptable material for next
> merge window (given that it's not a fix per-se) ? If so I'll resubmit
> later.

I need to check with Craig Gallek, because he was about to upstream a
change to make SO_REUSEPORT more scalable & sexy (like having an [e]BPF
filter to perform the selection in an array of sockets)