linux-kernel - Re: [PATCH] ARM: ftrace: Ensure code modifications are synchronised across all cpus

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Date:	Fri, 07 Dec 2012 10:28:54 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"Jon Medhurst (Tixy)" <tixy@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Russell King <linux@....linux.org.uk>,
	Ingo Molnar <mingo@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Rabin Vincent <rabin@....in>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: ftrace: Ensure code modifications are synchronised
 across all cpus

On Fri, 2012-12-07 at 14:55 +0000, Jon Medhurst (Tixy) wrote:
>  
> > But also realize that function tracing is special :-) We have no cases
> > like this. The instruction being replaced is a call to mcount. In fact,
> > we replace it at boot with a nop. And this method only replaces that nop
> > into a call to function tracer, or replaces the call to function tracer
> > back to a nop. Always at the start of the function, and never involved
> > with conditionals. This limitation that function tracing imposes on what
> > we replace makes things a bit more sane in how we replace it.
> 
> Then perhaps the method you suggest will work on ARM :-). However, that
> is not something I personally propose to implement at this time. (I was
> doing my good Samaritan act by trying to fix the crashes which another
> team was getting when trying to use ftrace.)
> 

I'm not NACKing your previous patch, I was just suggesting to bring ARM
up to the future :-)

I have no problems with the patch, but I just want to put it out there
that there's better ways. It's part of the remove stomp_machine()
crusade ;-)

-- Steve


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