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

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Date:	Mon, 4 Nov 2013 15:35:17 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Namhyung Kim <namhyung@...nel.org>
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 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.

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