linux-kernel - Re: BUG - function tracing with breakpoints

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Date:	Fri, 25 May 2012 16:51:26 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, Andi Kleen <ak@...ux.intel.com>
Subject: Re: BUG - function tracing with breakpoints

On Fri, 2012-05-25 at 14:46 -0400, Steven Rostedt wrote:
> On Fri, 2012-05-25 at 10:40 -0700, H. Peter Anvin wrote:
> > On 05/25/2012 08:29 AM, Steven Rostedt wrote:
> > > 
> > > This would make sense for this bug, as if modifying_ftrace_code was not
> > > seen by other CPUs, it wouldn't go into the ftrace_int3_handler() path.
> > > That would cause this issue. But the bug remains after the smp_mb()'s
> > > were put in place. Although it behaves a little differently not. Maybe
> > > there's something else I missed?
> > > 
> > 
> > Perhaps you should make the modifying_ftrace_code modification atomic...
> > it seems odd to have it not be atomic when it is clearly accessed across
> > CPUs that way.
> 
> I guess I can make it atomic. Not really a big deal as this (and soon
> one other place) is the only place that changes its value.
> 
> I've found another place that may be causing harm, and I'm currently
> working on fixing it. Hopefully after that's done, this problem will go
> away.

Grumble, still faults, and the notifier that I was tracking down
happened to be for DIE_OOPS :-p


/me continues his search.

-- Steve


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