linux-kernel - Re: [PATCH][GIT PULL] tracing: Fix compile issue for trace_sched

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Message-ID: <20101021135041.GA2920@redhat.com>
Date:	Thu, 21 Oct 2010 09:50:41 -0400
From:	Jason Baron <jbaron@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	2nddept-manager@....hitachi.co.jp
Subject: Re: [PATCH][GIT PULL] tracing: Fix compile issue for
	trace_sched_wakeup.c

On Thu, Oct 21, 2010 at 01:03:28PM +0200, Peter Zijlstra wrote:
> On Thu, 2010-10-21 at 07:01 -0400, Steven Rostedt wrote:
> > On Thu, 2010-10-21 at 09:22 +0200, Peter Zijlstra wrote:
> > > On Thu, 2010-10-21 at 11:58 +0900, Masami Hiramatsu wrote:
> > > 
> > > > It seems there can be a bug in stop_machine() routine under
> > > > heavy use. usually that is called just once at a time, but jump
> > > > label and optprobe might call it heavily (thousands times?).
> > > > So some racy situation can be happen easily.
> > > 
> > > There are people doing hotplug stress testing, that too results in heavy
> > > stop_machine usage.
> > 
> > But with hotplug, isn't there a bit more time between stop machine
> > calls? That is, you need to do a bit of work to bring down or up a CPU,
> > and that will slow down the number of stop machine calls together.
> > 
> > Here, we do a simple change and call stop machine() several times.
> > 
> > Although, I agree, I do not think the bug is in stop machine itself, but
> > perhaps the way we are using it might have some niche anomaly that we
> > are hitting.
> 
> Possibly, but wouldn't it make sense to batch up the work and simply
> call stop_machine only once? I mean, if you already know you're going to
> do this...
> 

it would. I know Masami is working on text_poke_smp_batch(), and I was
planning to move to it when it was ready...nonetheless there is still a
bug here...

thanks,

-Jason

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