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Date: Tue, 09 Jul 2013 17:20:17 +0900
From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Organization: Hitachi, Ltd., Japan
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To: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Andrew Morton <akpm@linux-foundation.org>, jovi.zhangwei@huawei.com,
        Jiri Olsa <jolsa@redhat.com>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Subject: Re: Re: [RFC PATCH] tracing/kprobe: Wait for disabling all running
 kprobe handlers
References: <20130708142533.GA23749@redhat.com> <20130709080145.7975.83164.stgit@mhiramat-M0-7522> <20130709080744.GH25631@dyad.programming.kicks-ass.net>
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(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).

Thank you,

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