[PATCH v3] hrtimer: select housekeeping CPU during migration

[Costa Shulyupin]

During CPU-down hotplug, hrtimers may migrate to isolated CPUs,
compromising CPU isolation. This commit addresses this issue by
masking valid CPUs for hrtimers using housekeeping_cpumask(HK_TYPE_TIMER).

Suggested-by: Waiman Long <longman@xxxxxxxxxx>
Signed-off-by: Costa Shulyupin <costa.shul@xxxxxxxxxx>
Reviewed-by: Waiman Long <longman@xxxxxxxxxx>
Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
---

Changes in v3:
- fixed compilation errors
Changes in v2:
- [v1] https://lore.kernel.org/all/20240211135213.2518068-1-costa.shul@xxxxxxxxxx/
- reworded and rebased on next

---
 kernel/time/hrtimer.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index edb0f821dcea..6057fe2e179b 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -38,6 +38,7 @@
 #include <linux/sched/deadline.h>
 #include <linux/sched/nohz.h>
 #include <linux/sched/debug.h>
+#include <linux/sched/isolation.h>
 #include <linux/timer.h>
 #include <linux/freezer.h>
 #include <linux/compat.h>
@@ -2223,8 +2224,8 @@ static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
 
 int hrtimers_cpu_dying(unsigned int dying_cpu)
 {
+	int i, ncpu = cpumask_any_and(cpu_active_mask, housekeeping_cpumask(HK_TYPE_TIMER));
 	struct hrtimer_cpu_base *old_base, *new_base;
-	int i, ncpu = cpumask_first(cpu_active_mask);
 
 	tick_cancel_sched_timer(dying_cpu);
 
-- 
2.43.0