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Date: Mon, 4 Nov 2013 15:35:17 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Namhyung Kim <namhyung@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>, Namhyung Kim <namhyung.kim@lge.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Hyeoncheol Lee <cheol.lee@lge.com>,
        Hemant Kumar <hkshaw@linux.vnet.ibm.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        "zhangwei(Jovi)" <jovi.zhangwei@huawei.com>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Subject: Re: [PATCH 10/13] tracing/uprobes: Fetch args before reserving a
	ring buffer
Message-ID: <20131104143517.GA4440@redhat.com>
References: <1383029621-7384-1-git-send-email-namhyung@kernel.org> <1383029621-7384-11-git-send-email-namhyung@kernel.org> <20131031181654.GA11208@redhat.com> <87y554382a.fsf@sejong.aot.lge.com>
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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.

Oleg.