To: j.mell@t-online.de
Cc: Steven Rostedt <rostedt@goodmis.org>, linux-kernel@vger.kernel.org,
       suresh.b.siddha@intel.com, arjan@linux.intel.com
Subject: Re: CONFIG_PREEMPT causes corruption of application's FPU stack
From: Andi Kleen <andi@firstfloor.org>
References: <200806011101.06491.j.mell@t-online.de>
Date: Sun, 01 Jun 2008 13:40:27 +0200
In-Reply-To: <200806011101.06491.j.mell@t-online.de> (j. mell's message of "Sun, 1 Jun 2008 11:01:06 +0200")
Message-ID: <87wsl9fkno.fsf@basil.nowhere.org>
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j.mell@t-online.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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