Re: [PATCH] trace_branch: use per-cpu counters for correct/incorrect stats

[Steven Rostedt]

On Mon, 29 Jun 2026 16:58:38 +0700
Martin Weiss <martin.githubacc@xxxxxxxxx> wrote:

> Replace per-task counters with per-cpu increments to avoid race
> conditions in the branch profiler fast path.
> 
> Fixes FIXME about atomicity.
> 
> Signed-off-by: Martin Weiss <Martin.weiss2410@xxxxxxxxx>
> ---
>  kernel/trace/trace_branch.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
> index d8e97ad798f0..960bcb3d7dbf 100644
> --- a/kernel/trace/trace_branch.c
> +++ b/kernel/trace/trace_branch.c
> @@ -213,11 +213,11 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
>  	 */
>  	trace_likely_condition(f, val, expect);
>  
> -	/* FIXME: Make this atomic! */
> +	/* use per-cpu counters to avoid contention */
>  	if (val == expect)
> -		f->data.correct++;
> +		this_cpu_inc(f->data.correct);
>  	else
> -		f->data.incorrect++;
> +		this_cpu_inc(f->data.incorrect);

I don't think this does what you think it does.

Did you even test this? I'm guessing it would blow up in some fantastic
ways.

NAK.

-- Steve


>  
>  	user_access_restore(flags);
>  }