# Re: \[PATCH v6 1/2\] ftrace: disable preemption when recursion locked

- From: 王贇 \<hidden\>
- Date: 2021-10-27 03:09:41 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2021/10/1555156
- Thread: https://ratatoskr.run/linuxppc-dev/2021/10/1555124/t.md

```text


On 2021/10/27 上午10:55, Steven Rostedt wrote:
> On Wed, 27 Oct 2021 10:34:13 +0800
> 王贇 [ref] wrote:
> 
>> +/*
>> + * Preemption will be enabled (if it was previously enabled).
>> + */
>>  static __always_inline void trace_clear_recursion(int bit)
>>  {
>> +	WARN_ON_ONCE(bit < 0);
> 
> Can you send a v7 without the WARN_ON.
> 
> This is an extremely hot path, and this will cause noticeable overhead.
> 
> If something were to call this with bit < 0, then it would crash and
> burn rather quickly.

I see, if the problem will be notified anyway then it's fine, v7 on the way.

Regards,
Michael Wang

> 
> -- Steve
> 
> 
>> +
>> +	preempt_enable_notrace();
>>  	barrier();
>>  	trace_recursion_clear(bit);
>>  }
```