netdev - Re: crash in __kfree_skb on v3.18-rc5 with CONFIG_DEBUG

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Message-ID: <1416588426.24312.6@mail.thefacebook.com>
Date:	Fri, 21 Nov 2014 11:47:06 -0500
From:	Chris Mason <clm@...com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	<netdev@...r.kernel.org>
Subject: Re: crash in __kfree_skb on v3.18-rc5 with CONFIG_DEBUG_PAGEALLOC



On Fri, Nov 21, 2014 at 11:37 AM, Eric Dumazet <eric.dumazet@...il.com> 
wrote:
> On Fri, 2014-11-21 at 08:31 -0800, Eric Dumazet wrote:
> 
>>  Can you double check, or send whole __kfree_skb() disassembly ?
>> 
>>  I do not understand how skb->fclone could possibly trap _at_ this 
>> point.
> 
> Oh well, I think commit ce1a4ea3f1258 ("net: avoid one atomic 
> operation
> in skb_clone()") is the problem, I'll send a revert.

Once my current run is done, I can revert this and try a loop.  But I 
don't see how this commit causes a use-after-free on the skb itself?

-chris



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