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

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Message-ID: <1271321507.16881.2244.camel@edumazet-laptop>
Date:	Thu, 15 Apr 2010 10:51:47 +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 jeudi 15 avril 2010 à 01:26 -0700, David Miller a écrit :
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Thu, 15 Apr 2010 10:02:33 +0200
> 
> > 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...
> 
> Ok, I thought your patch was specifically meant to fix Denys's bug.
> 
> The confusion comes from the fact that you mention Denys's crash in
> your commit message:
> 
> --------------------
> 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.
> --------------------
> 
> Anyways, I studied your patch once more and read the thread discussion
> with Krishna again and your patch looks fine.  I'll apply it to
> net-2.6, thanks!
> 

In any case, I think there is a fundamental problem with this sk
caching. Because one packet can travel in many stacked devices before
hitting the wire.

(bonding, vlan, ethernet) for example.

Socket cache is meaningfull for one level only...



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