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

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Date:	Thu, 09 Jun 2011 01:02:13 +0800
From:	Brad Campbell <brad@...rfbargle.com>
To:	Eric Dumazet <eric.dumazet@...il.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

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.
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