linux-kernel - Re: [PATCH] Linux Kernel Markers

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Message-Id: <1158748226.7705.0.camel@localhost.localdomain>
Date:	Wed, 20 Sep 2006 11:30:26 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Helge Hafting <helge.hafting@...el.hist.no>
Cc:	prasanna@...ibm.com, Martin Bligh <mbligh@...gle.com>,
	Andrew Morton <akpm@...l.org>,
	"Frank Ch. Eigler" <fche@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Paul Mundt <lethal@...ux-sh.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Jes Sorensen <jes@....com>, Tom Zanussi <zanussi@...ibm.com>,
	Richard J Moore <richardj_moore@...ibm.com>,
	Michel Dagenais <michel.dagenais@...ymtl.ca>,
	Christoph Hellwig <hch@...radead.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	William Cohen <wcohen@...hat.com>, ltt-dev@...fik.org,
	systemtap@...rces.redhat.com
Subject: Re: [PATCH] Linux Kernel Markers

Ar Mer, 2006-09-20 am 11:39 +0200, ysgrifennodd Helge Hafting:
> Yes, 5 bytes is not an atomic write except on 64-bit. So a race is possible.

Untrue as well. Pentium and later have CMPXCHG8.

> How about this workaround:
> 1. Overwrite the start of the function with a hlt, which is atomic.
> 2. Write that 5-byte jump after the hlt.
> 3. Overwrite the hlt with nop so things will work
> 4. interrupt any cpus that got stuck on the hlt - or just wait for the 
> timer.

CPU errata time again. You have to synchronize.

Alan

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