netdev - Re: KVM induced panic on 2.6.38[2367] & 2.6.39

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Date:	Wed, 08 Jun 2011 23:22:29 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Brad Campbell <brad@...rfbargle.com>
Cc:	Patrick McHardy <kaber@...sh.net>,
	Bart De Schuymer <bdschuym@...dora.be>, kvm@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org
Subject: Re: KVM induced panic on 2.6.38[2367] & 2.6.39

Le jeudi 09 juin 2011 à 01:02 +0800, Brad Campbell a écrit :
> On 08/06/11 11:59, Eric Dumazet wrote:
> 
> > Well, a bisection definitely should help, but needs a lot of time in
> > your case.
> 
> Yes. compile, test, crash, walk out to the other building to press 
> reset, lather, rinse, repeat.
> 
> I need a reset button on the end of a 50M wire, or a hardware watchdog!
> 
> Actually it's not so bad. If I turn off slub debugging the kernel panics 
> and reboots itself.
> 
> This.. :
> [    2.913034] netconsole: remote ethernet address 00:16:cb:a7:dd:d1
> [    2.913066] netconsole: device eth0 not up yet, forcing it
> [    3.660062] Refined TSC clocksource calibration: 3213.422 MHz.
> [    3.660118] Switching to clocksource tsc
> [   63.200273] r8169 0000:03:00.0: eth0: unable to load firmware patch 
> rtl_nic/rtl8168e-1.fw (-2)
> [   63.223513] r8169 0000:03:00.0: eth0: link down
> [   63.223556] r8169 0000:03:00.0: eth0: link down
> 
> ..is slowing down reboots considerably. 3.0-rc does _not_ like some 
> timing hardware in my machine. Having said that, at least it does not 
> randomly panic on SCSI like 2.6.39 does.
> 
> Ok, I've ruled out TCPMSS. Found out where it was being set and neutered 
> it. I've replicated it with only the single DNAT rule.
> 
> 
> > Could you try following patch, because this is the 'usual suspect' I had
> > yesterday :
> >
> > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > index 46cbd28..9f548f9 100644
> > --- a/net/core/skbuff.c
> > +++ b/net/core/skbuff.c
> > @@ -792,6 +792,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
> >   		fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta;
> >   	}
> >
> > +#if 0
> >   	if (fastpath&&
> >   	size + sizeof(struct skb_shared_info)<= ksize(skb->head)) {
> >   		memmove(skb->head + size, skb_shinfo(skb),
> > @@ -802,7 +803,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
> >   		off = nhead;
> >   		goto adjust_others;
> >   	}
> > -
> > +#endif
> >   	data = kmalloc(size + sizeof(struct skb_shared_info), gfp_mask);
> >   	if (!data)
> >   		goto nodata;
> >
> >
> >
> 
> Nope.. that's not it. <sigh> That might have changed the characteristic 
> of the fault slightly, but unfortunately I got caught with a couple of 
> fsck's, so I only got to test it 3 times tonight.
> 
> It's unfortunate that this is a production system, so I can only take it 
> down between about 9pm and 1am. That would normally be pretty 
> productive, except that an fsck of a 14TB ext4 can take 30 minutes if it 
> panics at the wrong time.
> 
> I'm out of time tonight, but I'll have a crack at some bisection 
> tomorrow night. Now I just have to go back far enough that it works, and 
> be near enough not to have to futz around with /proc /sys or drivers.
> 
> I really, really, really appreciate you guys helping me with this. It 
> has been driving me absolutely bonkers. If I'm ever in the same town as 
> any of you, dinner and drinks are on me.

Hmm, I wonder if kmemcheck could help you, but its slow as hell, so not
appropriate for production :(



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