[PATCH v2 2/2] sched/idle: Use hrtimer cleanup class in play_idle_precise()

[Hui Su]

Pair on-stack setup with destruction using the hrtimer_on_stack cleanup
class in play_idle_precise().

Keep the cleanup object's scope around timer start and the idle wait. Start
the timer in pinned hard mode, so its callback runs as a hardirq on the
current CPU. The interrupted task observes it.done only after the callback
returns. Since the callback returns HRTIMER_NORESTART, the timer is not
requeued before the cleanup object tears down its on-stack debug object.

Fixes: c1de45ca831a ("sched/idle: Add support for tasks that inject idle")
Signed-off-by: Hui Su <sh_def@xxxxxxx>
---
 kernel/sched/idle.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index eb73b65ce6c4..2880e01368b8 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -429,13 +429,17 @@ void play_idle_precise(u64 duration_ns, u64 latency_ns)
 	cpuidle_use_deepest_state(latency_ns);
 
 	it.done = 0;
-	hrtimer_setup_on_stack(&it.timer, idle_inject_timer_fn, CLOCK_MONOTONIC,
-			       HRTIMER_MODE_REL_HARD);
-	hrtimer_start(&it.timer, ns_to_ktime(duration_ns),
-		      HRTIMER_MODE_REL_PINNED_HARD);
+	{
+		CLASS(hrtimer_on_stack, timer)(&it.timer, idle_inject_timer_fn,
+					       CLOCK_MONOTONIC,
+					       HRTIMER_MODE_REL_HARD);
 
-	while (!READ_ONCE(it.done))
-		do_idle();
+		hrtimer_start(timer, ns_to_ktime(duration_ns),
+			      HRTIMER_MODE_REL_PINNED_HARD);
+
+		while (!READ_ONCE(it.done))
+			do_idle();
+	}
 
 	cpuidle_use_deepest_state(0);
 	current->flags &= ~PF_IDLE;
-- 
2.55.0