Re: [PATCH][GIT PULL] tracing: Fix compile issue fortrace_sched_wakeup.c

[Steven Rostedt]

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



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