linux-kernel - Re: Revert "gro: Fix legacy path napi_complete crash", (was: Re: Linux 2.6.29)

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Message-ID: <20090324143942.GA20462@elte.hu>
Date:	Tue, 24 Mar 2009 15:39:42 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Robert Schwebel <r.schwebel@...gutronix.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Frank Blaschka <blaschka@...ux.vnet.ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	kernel@...gutronix.de
Subject: Re: Revert "gro: Fix legacy path napi_complete crash", (was: Re:
	Linux 2.6.29)


* Robert Schwebel <r.schwebel@...gutronix.de> wrote:

> On Tue, Mar 24, 2009 at 02:02:02PM +0100, Ingo Molnar wrote:
> > If the box hung within 15 minutes, the kernel was deemed bad. Using 
> > that method i arrived to this upstream networking fix which was 
> > merged yesterday:
> > 
> >  | 303c6a0251852ecbdc5c15e466dcaff5971f7517 is first bad commit
> >  | commit 303c6a0251852ecbdc5c15e466dcaff5971f7517
> >  | Author: Herbert Xu <herbert@...dor.apana.org.au>
> >  | Date:   Tue Mar 17 13:11:29 2009 -0700
> >  |
> >  |     gro: Fix legacy path napi_complete crash
> 
> This commit breaks nfsroot booting on i.MX27 and other ARM boxes 
> with different network cards here in a reproducable way.

Can you confirm that Herbert's fix (see it below) solves the 
problem?

	Ingo

--------------->
>From b8b66ac07cab1b45aac93e4f406833a1e0d7677e Mon Sep 17 00:00:00 2001
From: Herbert Xu <herbert@...dor.apana.org.au>
Date: Tue, 24 Mar 2009 21:35:42 +0800
Subject: [PATCH] net: Fix netpoll lockup in legacy receive path

When I fixed the GRO crash in the legacy receive path I used
napi_complete to replace __napi_complete.  Unfortunately they're
not the same when NETPOLL is enabled, which may result in us
not calling __napi_complete at all.

While this is fishy in itself, let's make the obvious fix right
now of reverting to the previous state where we always called
__napi_complete.

Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Frank Blaschka <blaschka@...ux.vnet.ibm.com>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
LKML-Reference: <20090324133542.GA29046@...dor.apana.org.au>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 net/core/dev.c |   16 +++++++++-------
 1 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index e3fe5c7..523f53e 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2580,24 +2580,26 @@ static int process_backlog(struct napi_struct *napi, int quota)
 	int work = 0;
 	struct softnet_data *queue = &__get_cpu_var(softnet_data);
 	unsigned long start_time = jiffies;
+	struct sk_buff *skb;
 
 	napi->weight = weight_p;
 	do {
-		struct sk_buff *skb;
-
 		local_irq_disable();
 		skb = __skb_dequeue(&queue->input_pkt_queue);
-		if (!skb) {
-			local_irq_enable();
-			napi_complete(napi);
-			goto out;
-		}
 		local_irq_enable();
+		if (!skb)
+			break;
 
 		napi_gro_receive(napi, skb);
 	} while (++work < quota && jiffies == start_time);
 
 	napi_gro_flush(napi);
+	if (skb)
+		goto out;
+
+	local_irq_disable();
+	__napi_complete(napi);
+	local_irq_enable();
 
 out:
 	return work;
--
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