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Subject: Re: [PATCH][GIT PULL] tracing: Fix compile issue for
 trace_sched_wakeup.c
From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Jason Baron <jbaron@redhat.com>, Ingo Molnar <mingo@elte.hu>,
        LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
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Date: Thu, 21 Oct 2010 07:01:02 -0400
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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.

-- Steve