1 files changed, 11 insertions, 4 deletions

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 3319e16f31e5..7c7ec4515983 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -290,16 +290,17 @@ static int __init tick_nohz_full_setup(char *str)
 __setup("nohz_full=", tick_nohz_full_setup);
 
 static int tick_nohz_cpu_down_callback(struct notifier_block *nfb,
-                                                 unsigned long action,
-                                                 void *hcpu)
+                                       unsigned long action,
+                                       void *hcpu)
 {
         unsigned int cpu = (unsigned long)hcpu;
 
         switch (action & ~CPU_TASKS_FROZEN) {
         case CPU_DOWN_PREPARE:
                 /*
-                 * If we handle the timekeeping duty for full dynticks CPUs,
-                 * we can't safely shutdown that CPU.
+                 * The boot CPU handles housekeeping duty (unbound timers,
+                 * workqueues, timekeeping, ...) on behalf of full dynticks
+                 * CPUs. It must remain online when nohz full is enabled.
                  */
                 if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
                         return NOTIFY_BAD;
@@ -370,6 +371,12 @@ void __init tick_nohz_init(void)
         cpu_notifier(tick_nohz_cpu_down_callback, 0);
         pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
                 cpumask_pr_args(tick_nohz_full_mask));
+
+        /*
+         * We need at least one CPU to handle housekeeping work such
+         * as timekeeping, unbound timers, workqueues, ...
+         */
+        WARN_ON_ONCE(cpumask_empty(housekeeping_mask));
 }
 #endif