Re: [PATCH v2 6/6] sched/core: Pause KCOV in wake_up_new_task()

[Peter Zijlstra]

On Tue, Aug 11, 2026 at 05:41:11PM +0200, Karl Mehltretter wrote:
> wake_up_new_task() is uninstrumented, but CPU selection and enqueue call
> instrumented helpers. During a KCOV-enabled fork, they can record
> scheduler, hrtimer and clockevent coverage into the parent.
> 
> The paths depend on runqueue and CPU state, so coverage varies between
> identical forks. Pause KCOV for the whole function, extending the
> scheduler exclusion to new-task wakeups.
> 
> Fixes: 5c9a8750a640 ("kernel: add kcov code coverage")
> Assisted-by: Claude:claude-fable-5
> Signed-off-by: Karl Mehltretter <kmehltretter@xxxxxxxxx>
> ---
> Notes:
>     v2:
>      - take guard(kcov_pause)()
>      - reword the pause comment
> 
>  kernel/sched/core.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index e863fac02e38f..f7ddfbbb5a494 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4947,6 +4947,9 @@ void wake_up_new_task(struct task_struct *p)
>  	struct rq *rq;
>  	int wake_flags = WF_FORK;
>  
> +	/* Instrumented callees would leak coverage into current. */
> +	guard(kcov_pause)();

I'm sure you know what I'm about to say now, right?