cpu/hotplug: Create hotplug threads

In order to let the hotplugged cpu take care of the setup/teardown, we need a
seperate hotplug thread.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: Rik van Riel <riel@redhat.com>
Cc: Rafael Wysocki <rafael.j.wysocki@intel.com>
Cc: "Srivatsa S. Bhat" <srivatsa@mit.edu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Turner <pjt@google.com>
Link: http://lkml.kernel.org/r/20160226182341.454541272@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 9572ca0..9048c33 100644 (file)
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -22,6 +22,7 @@
 #include <linux/lockdep.h>
 #include <linux/tick.h>
 #include <linux/irq.h>
+#include <linux/smpboot.h>
 
 #include <trace/events/power.h>
 #define CREATE_TRACE_POINTS
@@ -33,10 +34,24 @@
  * cpuhp_cpu_state - Per cpu hotplug state storage
  * @state:     The current cpu state
  * @target:    The target state
+ * @thread:    Pointer to the hotplug thread
+ * @should_run:        Thread should execute
+ * @cb_stat:   The state for a single callback (install/uninstall)
+ * @cb:                Single callback function (install/uninstall)
+ * @result:    Result of the operation
+ * @done:      Signal completion to the issuer of the task
  */
 struct cpuhp_cpu_state {
        enum cpuhp_state        state;
        enum cpuhp_state        target;
+#ifdef CONFIG_SMP
+       struct task_struct      *thread;
+       bool                    should_run;
+       enum cpuhp_state        cb_state;
+       int                     (*cb)(unsigned int cpu);
+       int                     result;
+       struct completion       done;
+#endif
 };
 
 static DEFINE_PER_CPU(struct cpuhp_cpu_state, cpuhp_state);
@@ -394,6 +409,134 @@ static int cpuhp_up_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
        return ret;
 }
 
+/*
+ * The cpu hotplug threads manage the bringup and teardown of the cpus
+ */
+static void cpuhp_create(unsigned int cpu)
+{
+       struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
+
+       init_completion(&st->done);
+}
+
+static int cpuhp_should_run(unsigned int cpu)
+{
+       struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
+
+       return st->should_run;
+}
+
+/* Execute the teardown callbacks. Used to be CPU_DOWN_PREPARE */
+static int cpuhp_ap_offline(unsigned int cpu, struct cpuhp_cpu_state *st)
+{
+       enum cpuhp_state target = max((int)st->target, CPUHP_AP_ONLINE);
+
+       return cpuhp_down_callbacks(cpu, st, cpuhp_ap_states, target);
+}
+
+/* Execute the online startup callbacks. Used to be CPU_ONLINE */
+static int cpuhp_ap_online(unsigned int cpu, struct cpuhp_cpu_state *st)
+{
+       return cpuhp_up_callbacks(cpu, st, cpuhp_ap_states, st->target);
+}
+
+/*
+ * Execute teardown/startup callbacks on the plugged cpu. Also used to invoke
+ * callbacks when a state gets [un]installed at runtime.
+ */
+static void cpuhp_thread_fun(unsigned int cpu)
+{
+       struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
+       int ret = 0;
+
+       /*
+        * Paired with the mb() in cpuhp_kick_ap_work and
+        * cpuhp_invoke_ap_callback, so the work set is consistent visible.
+        */
+       smp_mb();
+       if (!st->should_run)
+               return;
+
+       st->should_run = false;
+
+       /* Single callback invocation for [un]install ? */
+       if (st->cb) {
+               if (st->cb_state < CPUHP_AP_ONLINE) {
+                       local_irq_disable();
+                       ret = cpuhp_invoke_callback(cpu, st->cb_state, st->cb);
+                       local_irq_enable();
+               } else {
+                       ret = cpuhp_invoke_callback(cpu, st->cb_state, st->cb);
+               }
+       } else {
+               /* Regular hotplug work */
+               if (st->state < st->target)
+                       ret = cpuhp_ap_online(cpu, st);
+               else if (st->state > st->target)
+                       ret = cpuhp_ap_offline(cpu, st);
+       }
+       st->result = ret;
+       complete(&st->done);
+}
+
+/* Invoke a single callback on a remote cpu */
+static int cpuhp_invoke_ap_callback(int cpu, enum cpuhp_state state,
+                                   int (*cb)(unsigned int))
+{
+       struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
+
+       if (!cpu_online(cpu))
+               return 0;
+
+       st->cb_state = state;
+       st->cb = cb;
+       /*
+        * Make sure the above stores are visible before should_run becomes
+        * true. Paired with the mb() above in cpuhp_thread_fun()
+        */
+       smp_mb();
+       st->should_run = true;
+       wake_up_process(st->thread);
+       wait_for_completion(&st->done);
+       return st->result;
+}
+
+/* Regular hotplug invocation of the AP hotplug thread */
+static int cpuhp_kick_ap_work(unsigned int cpu)
+{
+       struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
+       enum cpuhp_state state = st->state;
+
+       trace_cpuhp_enter(cpu, st->target, state, cpuhp_kick_ap_work);
+       st->result = 0;
+       st->cb = NULL;
+       /*
+        * Make sure the above stores are visible before should_run becomes
+        * true. Paired with the mb() above in cpuhp_thread_fun()
+        */
+       smp_mb();
+       st->should_run = true;
+       wake_up_process(st->thread);
+       wait_for_completion(&st->done);
+       trace_cpuhp_exit(cpu, st->state, state, st->result);
+       return st->result;
+}
+
+static struct smp_hotplug_thread cpuhp_threads = {
+       .store                  = &cpuhp_state.thread,
+       .create                 = &cpuhp_create,
+       .thread_should_run      = cpuhp_should_run,
+       .thread_fn              = cpuhp_thread_fun,
+       .thread_comm            = "cpuhp/%u",
+       .selfparking            = true,
+};
+
+void __init cpuhp_threads_init(void)
+{
+       BUG_ON(smpboot_register_percpu_thread(&cpuhp_threads));
+       kthread_unpark(this_cpu_read(cpuhp_state.thread));
+}
+
 #ifdef CONFIG_HOTPLUG_CPU
 EXPORT_SYMBOL(register_cpu_notifier);
 EXPORT_SYMBOL(__register_cpu_notifier);
@@ -997,7 +1140,7 @@ static int cpuhp_cb_check(enum cpuhp_state state)
 
 static bool cpuhp_is_ap_state(enum cpuhp_state state)
 {
-       return (state > CPUHP_AP_OFFLINE && state < CPUHP_AP_ONLINE);
+       return (state >= CPUHP_AP_OFFLINE && state <= CPUHP_AP_ONLINE);
 }
 
 static struct cpuhp_step *cpuhp_get_step(enum cpuhp_state state)

diff --git a/kernel/smp.c b/kernel/smp.c
index d903c02..822ffb1 100644 (file)
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -569,6 +569,7 @@ void __init smp_init(void)
        unsigned int cpu;
 
        idle_threads_init();
+       cpuhp_threads_init();
 
        /* FIXME: This should be done in userspace --RR */
        for_each_present_cpu(cpu) {

diff --git a/kernel/smpboot.h b/kernel/smpboot.h
index 6b5f020..485b81c 100644 (file)
--- a/kernel/smpboot.h
+++ b/kernel/smpboot.h
@@ -17,4 +17,6 @@ int smpboot_create_threads(unsigned int cpu);
 int smpboot_park_threads(unsigned int cpu);
 int smpboot_unpark_threads(unsigned int cpu);
 
+void __init cpuhp_threads_init(void);
+
 #endif