Date: Tue, 9 Jul 2013 10:21:49 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
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
Message-ID: <20130709082149.GK25631@dyad.programming.kicks-ass.net>
References: <20130708142533.GA23749@redhat.com>
 <20130709080145.7975.83164.stgit@mhiramat-M0-7522>
 <20130709080744.GH25631@dyad.programming.kicks-ass.net>
 <51DBC7C1.9000601@hitachi.com>
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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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