netdev - Re: [PATCH] net: fix race in process

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Message-ID: <20071003150519.1fd206a8@freepuppy.rosehill>
Date:	Wed, 3 Oct 2007 15:05:19 -0700
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	David Miller <davem@...emloft.net>
Cc:	a.p.zijlstra@...llo.nl, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, jdike@...toit.com
Subject: Re: [PATCH] net: fix race in process_backlog

On Wed, 03 Oct 2007 14:58:07 -0700 (PDT)
David Miller <davem@...emloft.net> wrote:

> From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Date: Wed, 03 Oct 2007 17:44:53 +0200
> 
> > Index: linux-2.6/net/core/dev.c
> > ===================================================================
> > --- linux-2.6.orig/net/core/dev.c
> > +++ linux-2.6/net/core/dev.c
> > @@ -2095,11 +2095,11 @@ static int process_backlog(struct napi_s
> >  
> >  		local_irq_disable();
> >  		skb = __skb_dequeue(&queue->input_pkt_queue);
> > -		local_irq_enable();
> >  		if (!skb) {
> > -			napi_complete(napi);
> > +			__napi_complete(napi);
> >  			break;
> >  		}
> > +		local_irq_enable();
> 
> What re-enables interrupts in the !skb path?

This looks like a better fix. the irq_enable is needed in both cases.

--- a/net/core/dev.c	2007-09-27 07:19:10.000000000 -0700
+++ b/net/core/dev.c	2007-10-03 15:03:54.000000000 -0700
@@ -2077,12 +2077,14 @@ static int process_backlog(struct napi_s
 
 		local_irq_disable();
 		skb = __skb_dequeue(&queue->input_pkt_queue);
-		local_irq_enable();
 		if (!skb) {
-			napi_complete(napi);
+			__napi_complete(napi);
+			local_irq_enable();
 			break;
 		}
 
+		local_irq_enable();
+
 		dev = skb->dev;
 
 		netif_receive_skb(skb);


-- 
Stephen Hemminger <shemminger@...ux-foundation.org>
-
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