linux-kernel - Re: Re: [RFC PATCH] tracing/kprobe: Wait for disabling all running kprobe handlers

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Message-ID: <20130709082149.GK25631@dyad.programming.kicks-ass.net>
Date:	Tue, 9 Jul 2013 10:21:49 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	jovi.zhangwei@...wei.com, Jiri Olsa <jolsa@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Subject: Re: Re: [RFC PATCH] tracing/kprobe: Wait for disabling all running
 kprobe handlers

On Tue, Jul 09, 2013 at 05:20:17PM +0900, Masami Hiramatsu wrote:
> (2013/07/09 17:07), Peter Zijlstra wrote:
> > On Tue, Jul 09, 2013 at 05:01:45PM +0900, Masami Hiramatsu wrote:
> >> +	if (wait) {
> >> +		/*
> >> +		 * synchronize with kprobe_trace_func/kretprobe_trace_func
> >> +		 * to ensure disabled (all running handlers are finished)
> >> +		 */
> >> +		synchronize_sched();
> >> +		kfree(link);	/* Ignored if link == NULL */
> >> +	}
> > 
> > What's not clear to me from this comment is if we're only waiting for kfree()?
> > In that case shouldn't we use call_rcu() to free the thing? Or do we need the
> > sync_sched() for other purposes as well?
> 
> No, this is not only for kfree, but also to ensure completing
> disabling process, because trace_remove_event_call() supposes
> that for releasing event_call related objects (Those objects
> will be accessed in the handlers).

Then may I kindly suggest you clarify this in the comment? :-)
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