Merge tag 'timers-urgent-2025-02-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull timer fixes from Ingo Molnar:
 "Fix a PREEMPT_RT bug in the clocksource verification code that caused
  false positive warnings.

  Also fix a timer migration setup bug when new CPUs are added"

* tag 'timers-urgent-2025-02-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  timers/migration: Fix off-by-one root mis-connection
  clocksource: Use migrate_disable() to avoid calling get_random_u32() in atomic context

Author: torvalds

kernel/time/clocksource.c

@@ -373,17 +373,18 @@ void clocksource_verify_percpu(struct clocksource *cs)
 	cpumask_clear(&cpus_ahead);
 	cpumask_clear(&cpus_behind);
 	cpus_read_lock();
-	preempt_disable();
+	migrate_disable();
 	clocksource_verify_choose_cpus();
 	if (cpumask_empty(&cpus_chosen)) {
-		preempt_enable();
+		migrate_enable();
 		cpus_read_unlock();
 		pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name);
 		return;
 	}
 	testcpu = smp_processor_id();
 	pr_info("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n",
 		cs->name, testcpu, cpumask_pr_args(&cpus_chosen));
+	preempt_disable();
 	for_each_cpu(cpu, &cpus_chosen) {
 		if (cpu == testcpu)
 			continue;
@@ -403,6 +404,7 @@ void clocksource_verify_percpu(struct clocksource *cs)
 			cs_nsec_min = cs_nsec;
 	}
 	preempt_enable();
+	migrate_enable();
 	cpus_read_unlock();
 	if (!cpumask_empty(&cpus_ahead))
 		pr_warn("        CPUs %*pbl ahead of CPU %d for clocksource %s.\n",

kernel/time/timer_migration.c

@@ -1675,6 +1675,9 @@ static int tmigr_setup_groups(unsigned int cpu, unsigned int node)
 
 	} while (i < tmigr_hierarchy_levels);
 
+	/* Assert single root */
+	WARN_ON_ONCE(!err && !group->parent && !list_is_singular(&tmigr_level_list[top]));
+
 	while (i > 0) {
 		group = stack[--i];
 
@@ -1716,7 +1719,12 @@ static int tmigr_setup_groups(unsigned int cpu, unsigned int node)
 		WARN_ON_ONCE(top == 0);
 
 		lvllist = &tmigr_level_list[top];
-		if (group->num_children == 1 && list_is_singular(lvllist)) {
+
+		/*
+		 * Newly created root level should have accounted the upcoming
+		 * CPU's child group and pre-accounted the old root.
+		 */
+		if (group->num_children == 2 && list_is_singular(lvllist)) {
 			/*
 			 * The target CPU must never do the prepare work, except
 			 * on early boot when the boot CPU is the target. Otherwise