linux-kernel - Re: Re: [PATCH] tracing/uprobes: Support ftrace_event

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Date:	Tue, 18 Jun 2013 10:31:36 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	paulmck@...ux.vnet.ibm.com,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"yrl.pp-manager.tt@...achi.com" <yrl.pp-manager.tt@...achi.com>
Subject: Re: Re: [PATCH] tracing/uprobes: Support ftrace_event_file base
 multibuffer

(2013/06/17 21:33), Steven Rostedt wrote:
> On Mon, 2013-06-17 at 11:54 +0900, Masami Hiramatsu wrote:
> 
>>> It makes a lot of sense to me, at least assuming no issues with the
>>> interrupts being disabled, but the checks not spotting this.  Here
>>> is the check:
>>>
>>> 	preempt_count() != 0 || irqs_disabled()
>>>
>>> (With additional elaboration for if lockdep is enabled.)
>>
>> OK, I see. So I'll convert all the rcu_dereference_raw() to
>> rcu_dereference_sched() except kprobe handler, because in the
>> kprobe handler above check always be true. :)
> 
> I would convert them all to rcu_dereference_sched(), the above check is
> only when CONFIG_DEBUG_LOCK_ALLOC is set. It also annotates what is
> protecting this variable. Please do not avoid a check because "it's
> always true here". You also get people copying that code (like for
> uprobes) and that will skip the check too.
> 
> The only reason ftrace function tracer uses the raw (and now
> raw_notrace) version is because it is extremely invasive, and these
> checks done at *every* function call can actually live lock the system.
> But other places in tracing use the appropriate rcu_dereference_*()
> functions. If they do not, then they need to be fixed too.

Oh, I see.
Anyway, it will be completely replaced by the Oleg's patch.
Or should I fix that before his work?

Thank you,

-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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