linux-kernel - Re: [PATCH 3/3] ftrace: Do not call stub functions in control loop

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Date:	Tue, 9 Apr 2013 10:41:50 +0800
From:	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	<linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	WANG Chao <chaowang@...hat.com>,
	Greg KH <gregkh@...uxfoundation.org>, <stable@...r.kernel.org>
Subject: Re: [PATCH 3/3] ftrace: Do not call stub functions in control loop

On 2013/4/9 10:16, Steven Rostedt wrote:
> On Tue, 2013-04-09 at 10:08 +0800, zhangwei(Jovi) wrote:
>> On 2013/4/9 4:49, Steven Rostedt wrote:
>>> From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>
>>>
>>> The function tracing control loop used by perf spits out a warning
>>> if the called function is not a control function. This is because
>>> the control function references a per cpu allocated data structure
>>> on struct ftrace_ops that is not allocated for other types of
>>> functions.
>>>
>>> commit 0a016409e42 "ftrace: Optimize the function tracer list loop"
>>>
>>> Had an optimization done to all function tracing loops to optimize
>>> for a single registered ops. Unfortunately, this allows for a slight
>>> race when tracing starts or ends, where the stub function might be
>>> called after the current registered ops is removed. In this case we
>>> get the following dump:
>>>
> 
>> Involve stable? 3.8 kernel user would need this fix.
> 
> Why? commit 0a016409e42 "ftrace: Optimize the function tracer list loop"
> was added for 3.9. 3.8 has:
> 
>         op = rcu_dereference_raw(ftrace_control_list);
>         while (op != &ftrace_list_end) {
>                 if (!ftrace_function_local_disabled(op) &&
>                     ftrace_ops_test(op, ip))
>                         op->func(ip, parent_ip, op, regs);
> 
>                 op = rcu_dereference_raw(op->next);
>         };
> 
> The stub function will never get called.
> 
> -- Steve
Hmm, You are right, I misunderstand tag info got by git describe in my local box

[root@...i linux]# git describe 0a016409e42
trace-3.8-rc4-fix-19-g0a01640

> 
> 
> 
> 
> .
> 


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