From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
To: paulmck@linux.vnet.ibm.com
Cc: Steven Rostedt <rostedt@goodmis.org>,
"zhangwei(Jovi)" <jovi.zhangwei@huawei.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
Ingo Molnar <mingo@redhat.com>, Oleg Nesterov <oleg@redhat.com>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"yrl.pp-manager.tt@hitachi.com" <yrl.pp-manager.tt@hitachi.com>
Subject: Re: [PATCH] tracing/uprobes: Support ftrace_event_file base multibuffer
Date: Mon, 17 Jun 2013 11:54:59 +0900 [thread overview]
Message-ID: <51BE7A83.9060802@hitachi.com> (raw)
In-Reply-To: <20130614172516.GP5146@linux.vnet.ibm.com>
(2013/06/15 2:25), Paul E. McKenney wrote:
> On Fri, Jun 14, 2013 at 12:33:27PM -0400, Steven Rostedt wrote:
>> On Fri, 2013-06-14 at 09:21 -0700, Paul E. McKenney wrote:
>>
>>>>>> @@ -548,15 +556,35 @@ static void uprobe_trace_print(struct trace_uprobe *tu,
>>>>>> /* uprobe handler */
>>>>>> static int uprobe_trace_func(struct trace_uprobe *tu, struct pt_regs *regs)
>>>>>> {
>>>>>> - if (!is_ret_probe(tu))
>>>>>> - uprobe_trace_print(tu, 0, regs);
>>>>>> + struct ftrace_event_file **file;
>>>>>> +
>>>>>> + if (is_ret_probe(tu))
>>>>>> + return 0;
>>>>>> +
>>>>>> + file = rcu_dereference_raw(tu->files);
>>>>
>>>> Why are you using rcu_dereference_raw() and not rcu_dereference(). The
>>>> _raw() is a bit special, and unless you know what you are doing with RCU
>>>> here, don't use it.
>>>>
>>>> As I see you using rcu_dereference_raw() all over this patch, along with
>>>> mutexes, I believe that you are not using RCU correctly here.
>>>
>>> If irqs and preempt are disabled, I suggest using rcu_dereference_sched().
>>> That is what it is there for. ;-)
>>
>> I believe this just copied what kprobes did, where irqs and preemption
>> is disabled. I don't believe that these probes have that same luxury.
>>
>> But that begs the question. Should we convert the rcu_dereference_raw()
>> in the kprobe code to rcu_dereference_sched()?
>
> 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. :)
Thank you,
--
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com
next prev parent reply other threads:[~2013-06-17 2:55 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-14 1:44 [PATCH] tracing/uprobes: Support ftrace_event_file base multibuffer zhangwei(Jovi)
2013-06-14 13:21 ` Masami Hiramatsu
2013-06-14 13:51 ` Oleg Nesterov
2013-06-14 14:09 ` Oleg Nesterov
2013-06-14 15:31 ` Steven Rostedt
2013-06-14 16:21 ` Paul E. McKenney
2013-06-14 16:33 ` Steven Rostedt
2013-06-14 17:25 ` Paul E. McKenney
2013-06-17 2:54 ` Masami Hiramatsu [this message]
2013-06-17 12:33 ` Steven Rostedt
2013-06-18 1:31 ` Masami Hiramatsu
2013-06-18 2:02 ` Steven Rostedt
2013-06-14 14:44 ` Oleg Nesterov
2013-06-14 16:04 ` ftrace multibuffer && rcu (Was: tracing/uprobes: Support ftrace_event_file base multibuffer) Oleg Nesterov
2013-06-14 16:18 ` Oleg Nesterov
2013-06-14 16:26 ` Steven Rostedt
2013-06-14 17:02 ` Oleg Nesterov
2013-06-20 16:43 ` [PATCH] tracing/uprobes: Support ftrace_event_file base multibuffer Oleg Nesterov
2013-06-21 8:17 ` zhangwei(Jovi)
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