# Re: \[PATCH v13 10/14\] unwind: Clear unwind\_mask on exit back to user space

- From: Steven Rostedt \<rostedt@goodmis.org\>
- Date: 2025-07-15 17:20:30 
- List: linux-trace-kernel
- Page: https://ratatoskr.run/linux-trace-kernel/2025/07/3135785
- Thread: https://ratatoskr.run/linux-trace-kernel/2025/07/3124621/t.md

```text
On Tue, 15 Jul 2025 12:29:12 +0200
Peter Zijlstra [ref] wrote:

> @@ -170,41 +193,62 @@ static void unwind_deferred_task_work(st
>  int unwind_deferred_request(struct unwind_work *work, u64 *cookie)
>  {
>  	struct unwind_task_info *info = &current->unwind_info;
> -	int ret;
> +	unsigned long bits, mask;
> +	int bit, ret;
>  
>  	*cookie = 0;
>  
> -	if (WARN_ON_ONCE(in_nmi()))
> -		return -EINVAL;
> -
>  	if ((current->flags & (PF_KTHREAD | PF_EXITING)) ||
>  	    !user_mode(task_pt_regs(current)))
>  		return -EINVAL;
>  
> +	/* NMI requires having safe cmpxchg operations */
> +	if (WARN_ON_ONCE(!UNWIND_NMI_SAFE && in_nmi()))
> +		return -EINVAL;

I don't think we want to have a WARN_ON() here as the perf series tries
to first do the deferred unwinding and if that fails, it will go back
to it's old method.

By having a WARN_ON(), we need to make perf aware of this limitation
too. Do we want to do that?

-- Steve
```