linux-kernel - Re: [PATCH] net: disable UDP punt on sockets in RCV

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Date:   Fri, 4 May 2018 16:44:52 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Chintan Shah <chintsha@...co.com>, davem@...emloft.net,
        kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
        kaber@...sh.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     kamensky@...co.com, takondra@...co.com,
        xe-linux-external@...co.com, enkechen@...co.com
Subject: Re: [PATCH] net: disable UDP punt on sockets in RCV_SHUTDWON



On 05/04/2018 02:08 PM, Chintan Shah wrote:
> A UDP application which opens multiple sockets with same local
> address/port combination (using SO_REUSEPORT/SO_REUSEADDR socket options);
> and issues connect to a remote socket (using one of these local socket).
> Now if the same socket, which issued connect, issues shutdown (SHUT_RD);
> packets would still be queued to this socket (if sent from same remote
> client, which the local socket connected to), and not delivered to the
> other socket in the normal state.
> 

Confusing changelog.

sk_shutdown is on a different cache line, so this additional fetch would cause
loss of performance if many sockets are scanned in the hash bucket.

If you are trying to add full 4-tuple hash table to UDP, and accept() ability,
this would require a bit more than this hack...