linux-kernel - [GIT PULL] timer fixes

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Message-ID: <Z6cjnBOBUxOq__Ni@gmail.com>
Date: Sat, 8 Feb 2025 10:27:56 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Frederic Weisbecker <frederic@...nel.org>,
	Waiman Long <longman@...hat.com>
Subject: [GIT PULL] timer fixes

Linus,

Please pull the latest timers/urgent Git tree from:

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

   # HEAD: 868c9037df626b3c245ee26a290a03ae1f9f58d3 timers/migration: Fix off-by-one root mis-connection

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.

 Thanks,

	Ingo

------------------>
Frederic Weisbecker (1):
      timers/migration: Fix off-by-one root mis-connection

Waiman Long (1):
      clocksource: Use migrate_disable() to avoid calling get_random_u32() in atomic context


 kernel/time/clocksource.c     |  6 ++++--
 kernel/time/timer_migration.c | 10 +++++++++-
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 77d9566d3aa6..2a7802ec480c 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -373,10 +373,10 @@ 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;
@@ -384,6 +384,7 @@ void clocksource_verify_percpu(struct clocksource *cs)
 	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",
diff --git a/kernel/time/timer_migration.c b/kernel/time/timer_migration.c
index 9cb9b6584ea1..2f6330831f08 100644
--- a/kernel/time/timer_migration.c
+++ b/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