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

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Message-ID: <20111025115425.GA1530@gondor.apana.org.au>
Date:	Tue, 25 Oct 2011 13:54:25 +0200
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	David Miller <davem@...emloft.net>
Cc:	eric.dumazet@...il.com, evonlanthen@...il.com,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	timo.teras@....fi
Subject: Re: PROBLEM: System call 'sendmsg' of process ospfd (quagga)
	causes kernel oops

On Thu, Oct 20, 2011 at 11:35:41AM +0200, Herbert Xu wrote:
>
> In the time being I'll look more closely at all the users of
> needed_headroom to see if there's anything we've missed.

OK I've reviewed all the users of needed_headroom and I haven't
found anything other than the cases that we have enumerated.

One thing I noticed is that the macro LL_ALLOCATED_SPACE is
completely bogus and buggy.  It applies the alignment to the
sum of headroom and tailroom.  However, the alignment is then
applied separately to the headroom when reserving, meaning that
we may end up with insufficient tailroom.

So I'm going to get rid of LL_ALLOCATED_SPACE completely and
replace it with explicit references to the tailroom as it doesn't
need the alignment anyway (The headroom needs alignment since
we use it to ensure the head is aligned).

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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