Re: [PATCH 5/5] sched: pause KCOV in wake_up_new_task()

[Bradley Morgan]

On 7 August 2026 21:50:27 BST, Karl Mehltretter <kmehltretter@xxxxxxxxx>
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-opus-4-8
>Signed-off-by: Karl Mehltretter <kmehltretter@xxxxxxxxx>

Reviewed-by: Bradley Morgan <include@xxxxxxxxx>


>---
> kernel/sched/core.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
>diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>index 1e562a7ff0afb..cad1b01063450 100644
>--- a/kernel/sched/core.c
>+++ b/kernel/sched/core.c
>@@ -4945,8 +4945,12 @@ void wake_up_new_task(struct task_struct *p)
> {
> 	struct rq_flags rf;
> 	struct rq *rq;
>+	unsigned int kcov_paused;
> 	int wake_flags = WF_FORK;
> 
>+	/* KCOV: sched/ is uninstrumented but the wakeup callees are not. */

I feel this comment is not the best.  I mean, it's more a opinion thing.

/* Instrumented callees would leak into current here... */

could be a good one. What do you think? :)


>+	kcov_paused = kcov_pause(current);
>+
> 	raw_spin_lock_irqsave(&p->pi_lock, rf.flags);
> 	WRITE_ONCE(p->__state, TASK_RUNNING);
> 	/*
>@@ -4976,6 +4980,7 @@ void wake_up_new_task(struct task_struct *p)
> 		rq_repin_lock(rq, &rf);
> 	}
> 	task_rq_unlock(rq, p, &rf);
>+	kcov_resume(current, kcov_paused);
> }
> 
> #ifdef CONFIG_PREEMPT_NOTIFIERS
>

Thanks!