nohz: Assert existing housekeepers when nohz full enabled

[deliverable/linux.git] / kernel / time / tick-sched.c

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 3319e16f31e58ed69534ab2fa7e5cd05d7b90d8f..7c7ec45159834a1b25576fbed037c9951f3c076f 100644 (file)
--- 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