linux-kernel - Re: [PATCH tracing/kprobes] kprobes: Disable booster when CONFIG

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Date:	Fri, 29 Jan 2010 12:08:17 -0500
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Fr??d??ric Weisbecker" <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>
Subject: Re: [PATCH tracing/kprobes] kprobes: Disable booster when
	CONFIG_PREEMPT=y

* Masami Hiramatsu (mhiramat@...hat.com) wrote:
> Ingo Molnar wrote:
> > 
> > * Masami Hiramatsu <mhiramat@...hat.com> wrote:
> > 
> >> Disable kprobe booster when CONFIG_PREEMPT=y, because it can't ensure that 
> >> all kernel threads preempted on kprobe's boosted slot run out from the slot 
> >> even using freeze_processes().
> > 
> > hm, this really sucks as it makes preemptible kernels perform worse. Is there 
> > no better solution?
> > 
> >> The booster on preemptive kernel will be resumed if synchronize_tasks() or 
> >> something like that is introduced.
> > 
> > such as this one?
> 
> Yes, I think this synchronize_tasks(), which just (sleeping) wait until
> all currently preempted tasks are wake up and scheduled, can ensure safety

If a task is set as stopped, and the preempted before calling schedule,
can this result in a preempted task staying in that state for an
arbitrary long period of time ? Or is there some mechanism prohibiting
that in the scheduler ?

Thanks,

Mathieu

> 
> Thank you,
> 
> -- 
> Masami Hiramatsu
> 
> Software Engineer
> Hitachi Computer Products (America), Inc.
> Software Solutions Division
> 
> e-mail: mhiramat@...hat.com
> 

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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