netdev - Re: NULL pointer dereference panic in stable (2.6.33.2), amd64

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Message-ID: <1271318553.16881.2161.camel@edumazet-laptop>
Date:	Thu, 15 Apr 2010 10:02:33 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	krkumar2@...ibm.com, netdev@...r.kernel.org,
	nuclearcat@...learcat.com
Subject: Re: NULL pointer dereference panic in stable (2.6.33.2), amd64

Le mercredi 14 avril 2010 à 23:52 -0700, David Miller a écrit :
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Mon, 12 Apr 2010 09:18:17 +0200
> 
> > [PATCH] net: dev_pick_tx() fix
> > 
> > When dev_pick_tx() caches tx queue_index on a socket, we must check
> > socket dst_entry matches skb one, or risk a crash later, as reported by
> > Denys Fedorysychenko, if old packets are in flight during a route
> > change, involving devices with different number of queues.
> > 
> > Bug introduced by commit a4ee3ce3
> > (net: Use sk_tx_queue_mapping for connected sockets)
> > 
> > Reported-by: Denys Fedorysychenko <nuclearcat@...learcat.com>
> > Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> 
> It looks like Denys is still getting crashes even with this patch
> applied.  And I also think there is some meric to some of Krishna's
> analysis.
> 


> To me it seems to make more sense to validate the SKB's queue against
> the real actual choosen device's range.
> 
> The socket queue index will catch up and eventually become valid
> because the dst reset will invalidate the queue setting, and we'll
> thus recompute it as needed, as Krishna stated.
> 

??? 


> So I'm tossing this patch for now since it doesn't even aparently
> fix the bug.

I am a bit lost here David.

Denys got a crash that we cannot explain yet. He said he has no
multiqueue devices, so obviously my patch cant help him.

But this patch was fixing a real issue, I believe I pointed it twice
already...

I'll try to setup an environment to trigger this bug for real, but this
will take time, my dev machines are not multiqueue.



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