linux-kernel - Re: CONFIG_PREEMPT causes corruption of application's FPU stack

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Message-ID: <87wsl9fkno.fsf@basil.nowhere.org>
Date:	Sun, 01 Jun 2008 13:40:27 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	j.mell@...nline.de
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	suresh.b.siddha@...el.com, arjan@...ux.intel.com
Subject: Re: CONFIG_PREEMPT causes corruption of application's FPU stack

j.mell@...nline.de writes:

> or it is restored more than 
> once. Please keep in mind, that I am always running two Einstein processes 
> simultaneously on my two cores!
> I am willing to do further testing of this problem if someone can give me a 
> hint how to continue.

My bet would have been actually on aa283f49276e7d840a40fb01eee6de97eaa7e012
because it does some nasty things (enable interrupts in the middle
of __switch_to).

I looked through the old patchkit and couldn't find any specific 
PREEMPT problems. All code it changes should run with preempt_off

You could verify with sticking WARN_ON_ONCE(preemptible()) into 
all the places acc207616a91a413a50fdd8847a747c4a7324167 
changes (__unlazy_fpu, math_state_restore) and see if that triggers
anywhere.

-Andi
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