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

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Message-ID: <45111F37.2060607@hitachi.com>
Date:	Wed, 20 Sep 2006 20:00:07 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	prasanna@...ibm.com
Cc:	Martin Bligh <mbligh@...gle.com>,
	Vara Prasad <prasadav@...ibm.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, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] Linux Kernel Markers

Hi,

S. P. Prasanna wrote:
> Some more coplicated method.
> How about inserting a (instruction size) number of breakpoints and
> wait untill all the threads gets scheduled atleast once (so that
> threads would hit the breakpoint, if their IPs are in the middle of
> instruction we want to replace with jump) and then replace with
> jump instruction.

I think there is no need to insert so many breakpoints.
Instead of that, you merely wait that all the threads which are
running on each processors at that time gets scheduled, if the kernel
is *NOT* preemptive.

If the kernel is preemptive, some threads might sleep on the target
address. In this case, we can use freeze_processes() to ensure safety.
This idea was proposed by Ingo.

Thanks,
-- 
Masami HIRAMATSU
2nd Research Dept.
Hitachi, Ltd., Systems Development Laboratory
E-mail: masami.hiramatsu.pt@...achi.com

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