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

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Date:	Tue, 11 Mar 2008 14:58:30 +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>:
> > 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.
>
>
> Hmm, my fix was intended to fix a gdb problem. Or rather the gdb
>  problem was already fixed by disabling some functionality and with
>  this patch the functionality would be reenabled again.
>
>  If it fixed a qemu problem too that's great but was unintended
>  on my part. In fact it is a little worrying because there should
>  be no user visible change. Can you double check by unapply/test/reapply/test
>  the patch really makes a difference?

I've not said it has 'fixed' my problem - I said it has exposed the
problem much faster.
But now when I've made a double test - I think I was wrong - I've been
probably judging too fast and its also probably depending on the
sunlight position, but now I can see that even with recent git kernel
without your patch I get the busy loop pretty quick :(.

>  > >  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 ?
>
>
> I don't know. Someone has to debug it.

But who :) ?

Zdenek
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