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

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Date:	Wed, 08 Jun 2011 05:59:01 +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 mercredi 08 juin 2011 à 08:18 +0800, Brad Campbell a écrit :
> On 08/06/11 06:57, Patrick McHardy wrote:
> > On 07.06.2011 20:31, Eric Dumazet wrote:
> >> Le mardi 07 juin 2011 à 17:35 +0200, Patrick McHardy a écrit :
> >>
> >>> The main suspects would be NAT and TCPMSS. Did you also try whether
> >>> the crash occurs with only one of these these rules?
> >>>
> >>>> I've just compiled out CONFIG_BRIDGE_NETFILTER and can no longer access
> >>>> the address the way I was doing it, so that's a no-go for me.
> >>>
> >>> That's really weird since you're apparently not using any bridge
> >>> netfilter features. It shouldn't have any effect besides changing
> >>> at which point ip_tables is invoked. How are your network devices
> >>> configured (specifically any bridges)?
> >>
> >> Something in the kernel does
> >>
> >> u16 *ptr = addr (given by kmalloc())
> >>
> >> ptr[-1] = 0;
> >>
> >> Could be an off-one error in a memmove()/memcopy() or loop...
> >>
> >> I cant see a network issue here.
> >
> > So far me neither, but netfilter appears to trigger the bug.
> 
> Would it help if I tried some older kernels? This issue only surfaced 
> for me recently as I only installed the VM's in question about 12 weeks 
> ago and have only just started really using them in anger. I could try 
> reproducing it on progressively older kernels to see if I can find one 
> that works and then bisect from there.

Well, a bisection definitely should help, but needs a lot of time in
your case.

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;


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