linux-kernel - Re: linux-next: add utrace tree

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Date:	Wed, 27 Jan 2010 11:58:06 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Tom Tromey <tromey@...hat.com>,
	Kyle Moffett <kyle@...fetthome.net>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Fr??d??ric Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	linux-next@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	utrace-devel@...hat.com, Thomas Gleixner <tglx@...utronix.de>,
	JimKeniston <jkenisto@...ibm.com>
Subject: Re: linux-next: add utrace tree

On Wed, 2010-01-27 at 11:55 +0100, Peter Zijlstra wrote:
> Right, so there's two aspects:
> 
>  1) concurrency when inserting the probe
>  2) concurrency when hitting the probe
> 
> 1) used to be dealt with by using utrace to stop all threads in the
> process and then writing the instruction. I suggested to CoW the page,
> modify the instruction, set the pagetable and flush tlbs at full speed
> -- the very thing you suggest here. 

Also, since executable maps are typically MAP_PRIVATE, you have to CoW
anyway in order to modify it and I would exclude MAP_SHARED from being
probable because then the modification could seep through into whatever
was backing that thing.

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