linux-kernel - Re: [PATCH 1/5] ftrace: Synchronize variable setting with breakpoints

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Date:	Thu, 31 May 2012 13:53:40 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"H. Peter Anvin" <hpa@...or.com>, Dave Jones <davej@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 1/5] ftrace: Synchronize variable setting with
 breakpoints

On Thu, 2012-05-31 at 19:40 +0200, Peter Zijlstra wrote:
> On Thu, 2012-05-31 at 10:08 -0400, Steven Rostedt wrote:
> > > Also, why does this stuff live in ftrace? I always thought you were
> > > going to replace text_poke() so everybody that uses cross-modifying code
> > > could profit?
> > 
> > I discussed this with Masami at Collaboration Summit. The two are
> > similar but also very different. But we want to start merging the two
> > together where it makes sense. 
> 
> Argh,. I so disagree. You're doing it backwards.
> 
> First you merge whatever is there, regardless of who came first.

The comment about coming first was more about 're-inventing' then about
merging. You can't reinvent something that didn't exist.

That said, I didn't even think about text poke while doing this. I was
just simply thinking about removing stop_machine from ftrace, that
required this. It was only a after thought that text_poke() could do the
same. And this came up at Collab, where I thought, oh yeah! we can
incorporate this with text poke.


> Then, when everybody doing text modification is using the same
> interface, do a second implementation using a Kconfig knob. If the scary
> new one breaks, no sweat, flip the config. If its proven stable, kill
> off the old one.

What do you suggest then? To revert the code and rewrite it so that
text_poke() does a similar thing?

-- Steve


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