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

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Message-ID: <20111018104504.GA15913@gondor.apana.org.au>
Date:	Tue, 18 Oct 2011 12:45:04 +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 12:23:43PM +0200, Eric Dumazet wrote:
> 
> You're right, if reallocations are OK in all paths.

If it wasn't OK then making needed_headroom constant won't work
anyway.

> We'll need to change LL_RESERVED_SPACE() / LL_RESERVED_SPACE_EXTRA() /
> LL_ALLOCATED_SPACE() macros and provide the [read once] values, instead
> of a [read once] pointer to values.

I'm not sure what you mean here.  I don't see any need to change
these macros.  All we need is to save the value in a local variable:

	hh_len = LL_RESERVED_SPACE(dev);

	skb = alloc_skb(hh_len + len);
	skb_reserve(skb, hh_len);

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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