linux-kernel - Re: PROBLEM: System call 'sendmsg' of process ospfd (quagga) causes kernel oops

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Message-ID: <20111018114945.GA16359@gondor.apana.org.au>
Date:	Tue, 18 Oct 2011 13:49:45 +0200
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Elmar Vonlanthen <evonlanthen@...il.com>,
	linux-kernel@...r.kernel.org, netdev <netdev@...r.kernel.org>,
	Timo Teräs <timo.teras@....fi>
Subject: Re: PROBLEM: System call 'sendmsg' of process ospfd (quagga)
	causes kernel oops

On Tue, Oct 18, 2011 at 01:37:58PM +0200, Eric Dumazet wrote:
>
> In the bug we try to fix, we have :
> 
> skb = sock_alloc_send_skb(sk, ... + LL_ALLOCATED_SPACE(rt->dst.dev) 
> 
> ... < increase of dev->needed_headroom by another cpu/task >
> 
> skb_reserve(skb, LL_RESERVED_SPACE(rt->dst.dev));

OK, in that case one fix would be to replace LL_ALLOCATED_SPACE
with its two constiuents so that they may be stored in local
variables for later use.

	hlen = LL_HEADROOM(skb);
	tlen = LL_TAILROOM(skb);
	skb_alloc_send_skb(sk, ... + LL_ALIGN(hlen + tlen));

	skb_reserve(skb, LL_ALIGN(hlen));

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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