linux-kernel - Re: [PATCH 10/13] tracing/uprobes: Fetch args before reserving a ring buffer

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Date:	Tue, 05 Nov 2013 10:12:46 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Namhyung Kim <namhyung.kim@....com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hyeoncheol Lee <cheol.lee@....com>,
	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	"zhangwei\(Jovi\)" <jovi.zhangwei@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH 10/13] tracing/uprobes: Fetch args before reserving a ring buffer

Hi Oleg,

On Mon, 4 Nov 2013 15:35:17 +0100, Oleg Nesterov wrote:
> Hi Namhyung,
>
> On 11/04, Namhyung Kim wrote:
>>
>> >>
>> >> +	if (atomic_dec_and_test(&uprobe_buffer_ref)) {
>> >> +		free_percpu(uprobe_cpu_buffer);
>> >> +		uprobe_cpu_buffer = NULL;
>> >> +	}
>> >> +
>> >>  	WARN_ON(!uprobe_filter_is_empty(&tu->filter));
>> >
>> > Do we really need atomic_t? probe_event_enable/disable is called under
>> > event_mutex and we rely on this fact anyway.
>>
>> Looking at the code, it seems probe_event_enable/disable() is called
>> without event_mutex when it called from sys_perf_event_open().
>
> Where?
>
> __ftrace_set_clr_event(), perf_trace_init() or perf_trace_destroy()
> hold event_mutex. We rely on this fact anyway.

Ah, you're right.  My eyes simply missed it. ;-)

Thanks,
Namhyung
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