Re: WARNING: at mm/slub.c:3357, kernel BUG at mm/slub.c:3413

[Eric Dumazet <eric.dumazet@gmail.com>]

Le lundi 21 novembre 2011 A  09:24 +0100, Markus Trippelsdorf a A(C)crit :
> On 2011.11.21 at 09:05 +0100, Markus Trippelsdorf wrote:
> > On 2011.11.21 at 08:44 +0800, Alex,Shi wrote:
> > > On Fri, 2011-11-18 at 20:02 +0800, Markus Trippelsdorf wrote:
> > > > On 2011.11.18 at 09:54 +0100, Markus Trippelsdorf wrote:
> > > > > On 2011.11.18 at 16:43 +0800, Alex,Shi wrote:
> > > > > > > > 
> > > > > > > > The dirty flag comes from a bunch of unrelated xfs patches from Christoph, that
> > > > > > > > I'm testing right now.
> > > > > > 
> > > > > > Where is the xfs patchset? I am wondering if it is due to slub code. 
> > > > 
> > > > I begin to wonder if this might be the result of a compiler bug. 
> > > > The kernel in question was compiled with gcc version 4.7.0 20111117. And
> > > > there was commit to the gcc repository today that looks suspicious:
> > > > http://gcc.gnu.org/viewcvs?view=revision&revision=181466
> > > > 
> > > 
> > > Tell us if it is still there and you can reproduce it.
> > 
> > Hm, just noticed the "3.2.0-rc1 panic on PowerPC" thread:
> > http://thread.gmane.org/gmane.linux.kernel/1215584
> > 
> > The backtraces look suspiciously similar to mine.
> 
> So everything points to commit 87fb4b7b533:
> "net: more accurate skb truesize"
> 
> Can you take a look Eric?


This commit was followed by a fix (for SLOB, since SLUB/SLAB were not
affected)

Check commit bc417e30f8df (net: Add back alignment for size for
__alloc_skb)

If current kernel still crash, I believe there is a problem elsewhere (a
refcounting problem) that makes underlying page being reused :

The ksize(skb->head) call in pskb_expand_head() assumes skb->head is a
valid zone, not an already freed one...

By the way, we probably can remove (almost dead) code from
pskb_expand_head() since we now place struct skb_shared_info at the end
of skb->head at skb creation.

I'll send this patch later for net-next

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 18a3ceb..5fd67a8 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -892,17 +892,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
 		fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta;
 	}
 
-	if (fastpath &&
-	    size + sizeof(struct skb_shared_info) <= ksize(skb->head)) {
-		memmove(skb->head + size, skb_shinfo(skb),
-			offsetof(struct skb_shared_info,
-				 frags[skb_shinfo(skb)->nr_frags]));
-		memmove(skb->head + nhead, skb->head,
-			skb_tail_pointer(skb) - skb->head);
-		off = nhead;
-		goto adjust_others;
-	}
-
 	data = kmalloc(size + sizeof(struct skb_shared_info), gfp_mask);
 	if (!data)
 		goto nodata;
@@ -935,7 +924,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
 	off = (data + nhead) - skb->head;
 
 	skb->head     = data;
-adjust_others:
 	skb->data    += off;
 #ifdef NET_SKBUFF_DATA_USES_OFFSET
 	skb->end      = size;








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