netdev - Re: [PATCH 1/1] net: Add SO_REUSEPORT_LISTEN

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Message-ID: <CALx6S35248apbWqtG+g2U99O=4UJqyAG0bJeuxhZWtShrpDF+w@mail.gmail.com>
Date:	Mon, 21 Dec 2015 12:38:27 -0800
From:	Tom Herbert <tom@...bertland.com>
To:	Willy Tarreau <w@....eu>
Cc:	Eric Dumazet <eric.dumazet@...il.com>, cgallek@...gle.com,
	Josh Snyder <josh@...e406.com>,
	Tolga Ceylan <tolga.ceylan@...il.com>,
	Aaron Conole <aconole@...heb.org>,
	"David S. Miller" <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/1] net: Add SO_REUSEPORT_LISTEN_OFF socket option as
 drain mode

On Fri, Dec 18, 2015 at 11:00 PM, Willy Tarreau <w@....eu> wrote:
> On Fri, Dec 18, 2015 at 06:38:03PM -0800, Eric Dumazet wrote:
>> 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)
>
> OK fine. Please note that I also considered using a new value instead of
> zero there but I preferred to avoid it since the man talked about zero/
> non-zero so I wanted to limit any API change. If Craig adds new values
> there then this is something we can reconsider.
>
Is there any reason why this turning off a soreuseport socket should
not apply to UDP also? (seems like we have a need to turn off RX but
not TX for a UDP socket).

Tom

> Have a nice week-end,
> Willy
>
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