linux-kernel - Re: [PATCH 2/3] tracing/kprobes: Kill probe_enable

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Date:	Mon, 17 Jun 2013 17:18:41 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	linux-kernel@...r.kernel.org,
	"yrl.pp-manager.tt@...achi.com" <yrl.pp-manager.tt@...achi.com>
Subject: Re: [PATCH 2/3] tracing/kprobes: Kill probe_enable_lock

On 06/17, Masami Hiramatsu wrote:
>
> (2013/06/17 2:21), Oleg Nesterov wrote:
> > enable_trace_probe() and disable_trace_probe() should not worry about
> > serialization, the caller (perf_trace_init or __ftrace_set_clr_event)
> > holds event_mutex.
> >
> > They are also called by kprobe_trace_self_tests_init(), but this __init
> > function can't race with itself or trace_events.c
>
> Right,
> For safety, we should comment this at the caller side,

Which caller do you mean?

The patch adds

	/*
	 * This and enable_trace_probe/disable_trace_probe rely on event_mutex
	 * held by the caller, __ftrace_set_clr_event().
	 */

above trace_probe_nr_files() but the next patch removes this function
with the comment...

Will you agree with this patch if I add something like

	/*
	 * called by perf_trace_init() or __ftrace_set_clr_event() under event_mutex
	 */

above kprobe_register() ? Perhaps it makes sense to add
lockdep_assert_held(&event_mutex) into the body?

And:

> because
> those calls are the reason why I have introduced this lock.

Please do not hesitate to nack this patch if you think that we should
keep probe_enable_lock for safety even if it is not currently needed.
In this case I'd suggest to move lock/unlock into kprobe_register()
but this is minor.

Oleg.

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