[PATCH 1/2] ftrace: disable preemption on the testing of recursion

[王贇]

On 2021/10/13 上午10:27, Steven Rostedt wrote:
> On Wed, 13 Oct 2021 09:50:17 +0800
> 王贇 <yun.wang at linux.alibaba.com> wrote:
> 
>>>> -	preempt_enable_notrace();
>>>>  	ftrace_test_recursion_unlock(bit);
>>>>  }  
>>>
>>> I don't like this change much. We have preempt_disable there not because 
>>> of ftrace_test_recursion, but because of RCU. ftrace_test_recursion was 
>>> added later. Yes, it would work with the change, but it would also hide 
>>> things which should not be hidden in my opinion.  
>>
>> Not very sure about the backgroup stories, but just found this in
>> 'Documentation/trace/ftrace-uses.rst':
>>
>>   Note, on success,
>>   ftrace_test_recursion_trylock() will disable preemption, and the
>>   ftrace_test_recursion_unlock() will enable it again (if it was previously
>>   enabled).
> 
> Right that part is to be fixed by what you are adding here.
> 
> The point that Miroslav is complaining about is that the preemption
> disabling is special in this case, and not just from the recursion
> point of view, which is why the comment is still required.

My bad... the title do confusing people, will rewrite it.

Regards,
Michael Wang

> 
> -- Steve
> 
> 
>>
>> Seems like this lock pair was supposed to take care the preemtion itself?