netdev - Re: Kernel oops with 2.6.26, padlock and ipsec: probably problem with fpu state changes

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Date:	Sat, 9 Aug 2008 21:31:38 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Wolfgang Walter <wolfgang.walter@...m.de>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	"viro@...IV.linux.org.uk" <viro@...IV.linux.org.uk>,
	"vegard.nossum@...il.com" <vegard.nossum@...il.com>
Subject: Re: Kernel oops with 2.6.26, padlock and ipsec: probably problem with fpu state changes

On Fri, Aug 08, 2008 at 04:11:21PM -0700, Suresh Siddha wrote:
>
> b) Looking deeper, do we need to disable interrupts in the kernel_fpu_begin()?
>    Is there a recursive case, where interrupt context also touches FPU/SSE
>    registers?

Even if there wasn't one before, there is going to be one now
because as you pointed out yourself, if we get an inbound IPsec
packet between any kernel_fpu_begin/kernel_fpu_end area, we could
get a nested kernel_fpu_end which puts us back to square one wrt
to the original race.

So clearly we need to think more about this issue.

Unless we can come up with a new solution quickly, I recommend
that we back out the FPU changes.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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