linux-kernel - [PATCH] hrtimer: select housekeeping CPU during migration

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Date: Sun, 11 Feb 2024 15:52:13 +0200
From: Costa Shulyupin <costa.shul@...hat.com>
To: Waiman Long <longman@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Cc: Costa Shulyupin <costa.shul@...hat.com>
Subject: [PATCH] hrtimer: select housekeeping CPU during migration

because during CPU deactivation a timer can migrate
to isolated CPU and break CPU isolation.

For reference see function get_nohz_timer_target,
which selects CPU for new timers from housekeeping_cpumask(HK_TYPE_TIMER)

Inspired by Waiman Long <longman@...hat.com>

Signed-off-by: Costa Shulyupin <costa.shul@...hat.com>
---
 kernel/time/hrtimer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index f82997cf53b6..460d916e24b7 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -2227,7 +2227,7 @@ static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
 int hrtimers_cpu_dying(unsigned int dying_cpu)
 {
 	struct hrtimer_cpu_base *old_base, *new_base;
-	int i, ncpu = cpumask_first(cpu_active_mask);
+	int i, ncpu = cpumask_any_and(cpu_active_mask, housekeeping(HK_TYPE_TIMER));
 	pr_debug("ncpu=%d, dying_cpu=%d\n", ncpu, dying_cpu);
 
 	tick_cancel_sched_timer(dying_cpu);
-- 
2.43.0