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

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Date:	Tue, 12 Aug 2008 08:39:38 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Wolfgang Walter <wolfgang.walter@...m.de>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"viro@...IV.linux.org.uk" <viro@...iv.linux.org.uk>,
	"vegard.nossum@...il.com" <vegard.nossum@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Kernel oops with 2.6.26, padlock and ipsec: probably problem with fpu state changes

On Mon, Aug 11, 2008 at 01:19:01PM -0700, Suresh Siddha wrote:
.
> we can't unconditionally do clts() in the process context. We have
> to disable pre-emption to avoid interactions with context switch and
> lazy restore. So there will be RT latency issues aswell.

Yes disabling preemption is the real killer.

This is just a quick band-aid.  Longer term we should add a task
flag that indicates the task is currently doing kernel FPU which
will tell the scheduler to clear TS the next time it's run.  That
way we won't need to disable preemtion or pollute the user task's
FPU used state.

Thanks,
-- 
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