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

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Message-ID: <20090324154717.GA7506@elte.hu>
Date:	Tue, 24 Mar 2009 16:47:17 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Robert Schwebel <r.schwebel@...gutronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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)


* Ingo Molnar <mingo@...e.hu> wrote:

> 
> * Herbert Xu <herbert@...dor.apana.org.au> wrote:
> 
> > On Tue, Mar 24, 2009 at 03:39:42PM +0100, Ingo Molnar wrote:
> > >
> > > Subject: [PATCH] net: Fix netpoll lockup in legacy receive path
> > 
> > Actually, this patch is still racy.  If some interrupt comes in
> > and we suddenly get the maximum amount of backlog we can still
> > hang when we call __napi_complete incorrectly.  It's unlikely
> > but we certainly shouldn't allow that.  Here's a better version.
> > 
> > net: Fix netpoll lockup in legacy receive path
> 
> ok - i'm testing with this now.

test failure on one of the boxes, interface got stuck after ~100K 
packets:

eth1      Link encap:Ethernet  HWaddr 00:13:D4:DC:41:12  
          inet addr:10.0.1.13  Bcast:10.0.1.255  Mask:255.255.255.0
          inet6 addr: fe80::213:d4ff:fedc:4112/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:22555 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1897 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:2435071 (2.3 MiB)  TX bytes:503790 (491.9 KiB)
          Interrupt:11 Base address:0x4000 

i'm going back to your previous version for now - it might still be 
racy but it worked well for about 1.5 hours of test-time.

	Ingo
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