linux-kernel - Re: [net-next-2.6 PATCH RFC] TCPCT part 1d: generate Responder Cookie

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Message-ID: <4AF0B0D2.4030905@gmail.com>
Date:	Tue, 03 Nov 2009 17:38:10 -0500
From:	William Allen Simpson <william.allen.simpson@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Linux Kernel Developers <linux-kernel@...r.kernel.org>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [net-next-2.6 PATCH RFC] TCPCT part 1d: generate Responder Cookie

Eric Dumazet wrote:
> This patch looks fine, but I dont see how this new function is used.
> 
> Some points :
> 
> 1) We are working hard to remove rwlocks from network stack, so please dont
> add a new one. You probably can use a seqlock or RCU, or a server handling 
> 10.000 connections request per second on many NIC will hit this rwlock.
> 
This is my attempt at using RCU, as seqlock didn't seem to apply (and is
missing any Documentation.)

After the discussion about context, one question that I have is the need
for the _bh suffix?

+		rcu_read_lock_bh();
+		memcpy(&xvp->cookie_bakery[0],
+		       &rcu_dereference(tcp_secret_generating)->secrets[0],
+		       sizeof(tcp_secret_generating->secrets));
+		rcu_read_unlock_bh();


Documentation/RCU/checklist.txt #7 says:

   One exception to this rule: rcu_read_lock() and rcu_read_unlock()
   may be substituted for rcu_read_lock_bh() and rcu_read_unlock_bh()
   in cases where local bottom halves are already known to be
   disabled, for example, in irq or softirq context.  Commenting
   such cases is a must, of course!  And the jury is still out on
   whether the increased speed is worth it.

View attachment "TCPCT+1d1.patch" of type "text/plain" (7146 bytes)