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

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Message-ID: <51DBCEBF.7010608@hitachi.com>
Date:	Tue, 09 Jul 2013 17:50:07 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Peter Zijlstra <peterz@...radead.org>
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: [RFC PATCH] tracing/kprobe: Wait for disabling all running kprobe
 handlers

(2013/07/09 17:21), Peter Zijlstra wrote:
> 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? :-)
> 

Ah, right! I'll update it :)

Thank you!

-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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