linux-kernel - Re: [tip:x86/urgent] x86: Fix bogus warning in apic_noop.apic

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Message-ID: <20091207180436.GC5489@lenovo>
Date:	Mon, 7 Dec 2009 21:04:36 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	mingo@...e.hu, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/urgent] x86: Fix bogus warning in
	apic_noop.apic_write()

On Mon, Dec 07, 2009 at 05:55:37PM +0100, Thomas Gleixner wrote:
...
> > And, btw if some code is trying to write to apic when
> > it's disabled via boot option -- it means the code is
> > buggy and this is not a false positive but rather proper
> > warning.
> > 
> > Thomas, if you've changed this code I suppose you saw some
> > warning triggered, right? Could you pointed me on it?
> 
> http://www.kerneloops.org/searchweek.php?search=native_apic_write_dummy
> 

Doh!

The most cases show inapropriate usage of apic->write() operation.
set_perf_event_pending() already fixed by
7d42896628202a551ad1107697cd215dc5fca099,
intel_init_thermal() fixed as well with
5ce4243dcefbbc43791ffc36e1be55067ceec916

(all was in -tip).

Though throttling code is just buggy and intel_init_thermal() should
check if cpu_has_apic. So the former code does exactly what
it should -- it catches inapropriate writes.

Thomas, I just don't know -- from my pov, write() is really different
from read(), since it implies that APIC changes it behaviour, it could
be timer setup, vector setup operation or whatever. I even doubt if
enabling IPI in apic-noop is a good idea (since perf code already
implemented to check apic presence by Peter and IPI is not called).

Though I'm not insisting, I simply don't have spare time at moment
to check all apic_writes() again :(

	-- Cyrill
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