netdev - Re: [PATCH] rps: tcp: fix rps_sock_flow

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Date:	Fri, 04 Jun 2010 15:57:34 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	therbert@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH] rps: tcp: fix rps_sock_flow_table table updates

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 03 Jun 2010 21:03:58 +0200

> I believe a moderate SYN flood attack can corrupt RFS flow table
> (rps_sock_flow_table), making RPS/RFS much less effective.
> 
> Even in a normal situation, server handling short lived sessions suffer
> from bad steering for the first data packet of a session, if another SYN
> packet is received for another session.
> 
> We do following action in tcp_v4_rcv() :
> 
> 	sock_rps_save_rxhash(sk, skb->rxhash);
> 
> We should _not_ do this if sk is a LISTEN socket, as about each
> packet received on a LISTEN socket has a different rxhash than
> previous one.
>  -> RPS_NO_CPU markers are spread all over rps_sock_flow_table.
> 
> Also, it makes sense to protect sk->rxhash field changes with socket
> lock (We currently can change it even if user thread owns the lock
> and might use rxhash)
> 
> This patch moves sock_rps_save_rxhash() to a sock locked section,
> and only for non LISTEN sockets.
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>

Applied.
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