During CPU-down hotplug, hrtimers may migrate to isolated CPUs,
compromising CPU isolation.

Address this issue by masking valid CPUs for hrtimers using
housekeeping_cpumask(HK_TYPE_TIMER).

Suggested-by: Waiman Long <longman@redhat.com>
Signed-off-by: Costa Shulyupin <costa.shul@redhat.com>
Reviewed-by: Waiman Long <longman@redhat.com>
---

Changes in v4:
- fixed description
Changes in v3:
- fixed compilation errors
Changes in v2:
- [v1] https://lore.kernel.org/all/20240211135213.2518068-1-costa.shul@redhat.com/
- 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 5a98b35b0576..1fd106af747d 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>
@@ -2225,8 +2226,8 @@ 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

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     56c2cb10120894be40c40a9bf0ce798da14c50f6
Gitweb:        https://git.kernel.org/tip/56c2cb10120894be40c40a9bf0ce798da14c50f6
Author:        Costa Shulyupin <costa.shul@redhat.com>
AuthorDate:    Thu, 22 Feb 2024 22:08:56 +02:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Thu, 22 Feb 2024 22:18:21 +01:00

hrtimer: Select housekeeping CPU during migration

During CPU-down hotplug, hrtimers may migrate to isolated CPUs,
compromising CPU isolation.

Address this issue by masking valid CPUs for hrtimers using
housekeeping_cpumask(HK_TYPE_TIMER).

Suggested-by: Waiman Long <longman@redhat.com>
Signed-off-by: Costa Shulyupin <costa.shul@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20240222200856.569036-1-costa.shul@redhat.com
---
 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 5a98b35..1fd106a 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>
@@ -2225,8 +2226,8 @@ 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);