perf/core: Document some hotplug bits

[deliverable/linux.git] / kernel / cpu.c

diff --git a/kernel/cpu.c b/kernel/cpu.c
index ff8059b76a853a28e1514ad3d45b8ded23590156..6ea42e8da861b05077d01a23e15bb140afffa605 100644 (file)
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -706,8 +706,9 @@ static int takedown_cpu(unsigned int cpu)
        else
                synchronize_rcu();
 
-       /* Park the hotplug thread */
+       /* Park the smpboot threads */
        kthread_park(per_cpu_ptr(&cpuhp_state, cpu)->thread);
+       smpboot_park_threads(cpu);
 
        /*
         * Prevent irq alloc/free while the dying cpu reorganizes the
@@ -755,14 +756,26 @@ static int notify_dead(unsigned int cpu)
        return 0;
 }
 
+static void cpuhp_complete_idle_dead(void *arg)
+{
+       struct cpuhp_cpu_state *st = arg;
+
+       complete(&st->done);
+}
+
 void cpuhp_report_idle_dead(void)
 {
        struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
 
        BUG_ON(st->state != CPUHP_AP_OFFLINE);
-       st->state = CPUHP_AP_IDLE_DEAD;
-       complete(&st->done);
        rcu_report_dead(smp_processor_id());
+       st->state = CPUHP_AP_IDLE_DEAD;
+       /*
+        * We cannot call complete after rcu_report_dead() so we delegate it
+        * to an online cpu.
+        */
+       smp_call_function_single(cpumask_first(cpu_online_mask),
+                                cpuhp_complete_idle_dead, st, 0);
 }
 
 #else
@@ -1159,6 +1172,10 @@ static struct cpuhp_step cpuhp_bp_states[] = {
                .teardown               = NULL,
                .cant_stop              = true,
        },
+       /*
+        * Preparatory and dead notifiers. Will be replaced once the notifiers
+        * are converted to states.
+        */
        [CPUHP_NOTIFY_PREPARE] = {
                .name                   = "notify:prepare",
                .startup                = notify_prepare,
@@ -1166,12 +1183,17 @@ static struct cpuhp_step cpuhp_bp_states[] = {
                .skip_onerr             = true,
                .cant_stop              = true,
        },
+       /* Kicks the plugged cpu into life */
        [CPUHP_BRINGUP_CPU] = {
                .name                   = "cpu:bringup",
                .startup                = bringup_cpu,
                .teardown               = NULL,
                .cant_stop              = true,
        },
+       /*
+        * Handled on controll processor until the plugged processor manages
+        * this itself.
+        */
        [CPUHP_TEARDOWN_CPU] = {
                .name                   = "cpu:teardown",
                .startup                = NULL,
@@ -1184,6 +1206,23 @@ static struct cpuhp_step cpuhp_bp_states[] = {
 /* Application processor state steps */
 static struct cpuhp_step cpuhp_ap_states[] = {
 #ifdef CONFIG_SMP
+       /* Final state before CPU kills itself */
+       [CPUHP_AP_IDLE_DEAD] = {
+               .name                   = "idle:dead",
+       },
+       /*
+        * Last state before CPU enters the idle loop to die. Transient state
+        * for synchronization.
+        */
+       [CPUHP_AP_OFFLINE] = {
+               .name                   = "ap:offline",
+               .cant_stop              = true,
+       },
+       /*
+        * Low level startup/teardown notifiers. Run with interrupts
+        * disabled. Will be removed once the notifiers are converted to
+        * states.
+        */
        [CPUHP_AP_NOTIFY_STARTING] = {
                .name                   = "notify:starting",
                .startup                = notify_starting,
@@ -1191,17 +1230,32 @@ static struct cpuhp_step cpuhp_ap_states[] = {
                .skip_onerr             = true,
                .cant_stop              = true,
        },
+       /* Entry state on starting. Interrupts enabled from here on. Transient
+        * state for synchronsization */
+       [CPUHP_AP_ONLINE] = {
+               .name                   = "ap:online",
+       },
+       /* Handle smpboot threads park/unpark */
        [CPUHP_AP_SMPBOOT_THREADS] = {
                .name                   = "smpboot:threads",
                .startup                = smpboot_unpark_threads,
-               .teardown               = smpboot_park_threads,
+               .teardown               = NULL,
        },
+       /*
+        * Online/down_prepare notifiers. Will be removed once the notifiers
+        * are converted to states.
+        */
        [CPUHP_AP_NOTIFY_ONLINE] = {
                .name                   = "notify:online",
                .startup                = notify_online,
                .teardown               = notify_down_prepare,
        },
 #endif
+       /*
+        * The dynamically registered state space is here
+        */
+
+       /* CPU is fully up and running. */
        [CPUHP_ONLINE] = {
                .name                   = "online",
                .startup                = NULL,
@@ -1219,9 +1273,11 @@ static int cpuhp_cb_check(enum cpuhp_state state)
 
 static bool cpuhp_is_ap_state(enum cpuhp_state state)
 {
-       if (state >= CPUHP_AP_OFFLINE && state <= CPUHP_AP_ONLINE)
-               return true;
-       return state > CPUHP_BRINGUP_CPU;
+       /*
+        * The extra check for CPUHP_TEARDOWN_CPU is only for documentation
+        * purposes as that state is handled explicitely in cpu_down.
+        */
+       return state > CPUHP_BRINGUP_CPU && state != CPUHP_TEARDOWN_CPU;
 }
 
 static struct cpuhp_step *cpuhp_get_step(enum cpuhp_state state)