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

- From: Steven Rostedt \<rostedt@goodmis.org\>
- Date: 2021-10-27 02:56:03 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2021/10/1555149
- Thread: https://ratatoskr.run/linuxppc-dev/2021/10/1555124/t.md

```text
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.

-- Steve


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