linux-kernel - Re: [PATCH REPOST] Run IST traps from user mode preemptive on process stack

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Date:	Tue, 11 Mar 2008 13:03:29 +0100
From:	"Zdenek Kabelac" <zdenek.kabelac@...il.com>
To:	"Andi Kleen" <andi@...stfloor.org>
Cc:	"Ingo Molnar" <mingo@...e.hu>, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, jkosina@...e.cz
Subject: Re: [PATCH REPOST] Run IST traps from user mode preemptive on process stack

2008/3/11, Andi Kleen <andi@...stfloor.org>:
> Run IST traps from user mode preemptive on process stack
>
>  [Repost. Please ack or nack. -Andi]
>
>  x86-64 has a few exceptions which run on special architecture
>  supported IST exception stacks: these are nmi, double fault, stack fault,
>   int 3, debug.
>
>  Previously they would check for a scheduling event on returning
>  if the original CPU state was user mode and then switch to a
>  process stack to schedule.
>
>  But the actual trap handler would still run on the IST stack
>  with preemption disabled.
>

Hi Andi

In my post where I've been showing BUG trace:

http://lkml.org/lkml/2008/3/10/157

I've mentioned my problem with busy looping in Qemu.

I'm not sure whether this is good or bad sign - but with this patch
you have posted,
I do not have to wait in qemu for minutes to get the 'busy-loop' - I
get the exact same loop almost instantly when I start  disk read of LV
partition and running my simple module insertion testcase.

>  This patch changes these traps instead to always switch
>  to the process stack when the trap originated from user mode.
>  For kernel traps it keeps running non preemptive on the IST stack
>   because that is much safer (e.g. to still get nmi watchdog events
>  out even when the process stack is corrupted)
>

So what should I check to get fixed my problem in qemu ?

Zdenek
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