timers/migration: Add mask for CPUs available in the hierarchy

Keep track of the CPUs available for timer migration in a cpumask. This
prepares the ground to generalise the concept of unavailable CPUs.

Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://patch.msgid.link/20251120145653.296659-3-gmonaco@redhat.com

diff --git a/kernel/time/timer_migration.c b/kernel/time/timer_migration.c
index 2cfebed35e225eb6ea861422982fceab739b9ed9..3325ca7989b3c0b49903e7c20a524208bdb1e33e 100644 (file)
--- a/kernel/time/timer_migration.c
+++ b/kernel/time/timer_migration.c
@@ -424,6 +424,12 @@ static struct tmigr_group *tmigr_root;
 
 static DEFINE_PER_CPU(struct tmigr_cpu, tmigr_cpu);
 
+/*
+ * CPUs available for timer migration.
+ * Protected by cpuset_mutex (with cpus_read_lock held) or cpus_write_lock.
+ */
+static cpumask_var_t tmigr_available_cpumask;
+
 #define TMIGR_NONE     0xFF
 #define BIT_CNT                8
 
@@ -1433,6 +1439,7 @@ static int tmigr_clear_cpu_available(unsigned int cpu)
        int migrator;
        u64 firstexp;
 
+       cpumask_clear_cpu(cpu, tmigr_available_cpumask);
        raw_spin_lock_irq(&tmc->lock);
        tmc->available = false;
        WRITE_ONCE(tmc->wakeup, KTIME_MAX);
@@ -1446,7 +1453,7 @@ static int tmigr_clear_cpu_available(unsigned int cpu)
        raw_spin_unlock_irq(&tmc->lock);
 
        if (firstexp != KTIME_MAX) {
-               migrator = cpumask_any_but(cpu_online_mask, cpu);
+               migrator = cpumask_any(tmigr_available_cpumask);
                work_on_cpu(migrator, tmigr_trigger_active, NULL);
        }
 
@@ -1461,6 +1468,7 @@ static int tmigr_set_cpu_available(unsigned int cpu)
        if (WARN_ON_ONCE(!tmc->tmgroup))
                return -EINVAL;
 
+       cpumask_set_cpu(cpu, tmigr_available_cpumask);
        raw_spin_lock_irq(&tmc->lock);
        trace_tmigr_cpu_available(tmc);
        tmc->idle = timer_base_is_idle();
@@ -1805,6 +1813,11 @@ static int __init tmigr_init(void)
        if (ncpus == 1)
                return 0;
 
+       if (!zalloc_cpumask_var(&tmigr_available_cpumask, GFP_KERNEL)) {
+               ret = -ENOMEM;
+               goto err;
+       }
+
        /*
         * Calculate the required hierarchy levels. Unfortunately there is no
         * reliable information available, unless all possible CPUs have been