smp/hotplug: Differentiate the AP completion between up and down

With lockdep-crossrelease we get deadlock reports that span cpu-up and
cpu-down chains. Such deadlocks cannot possibly happen because cpu-up
and cpu-down are globally serialized.

  takedown_cpu()
    irq_lock_sparse()
    wait_for_completion(&st->done)

                                cpuhp_thread_fun
                                  cpuhp_up_callback
                                    cpuhp_invoke_callback
                                      irq_affinity_online_cpu
                                        irq_local_spare()
                                        irq_unlock_sparse()
                                  complete(&st->done)

Now that we have consistent AP state, we can trivially separate the
AP completion between up and down using st->bringup.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: max.byungchul.park@gmail.com
Cc: bigeasy@linutronix.de
Cc: efault@gmx.de
Cc: rostedt@goodmis.org
Link: https://lkml.kernel.org/r/20170920170546.872472799@infradead.org

diff --git a/kernel/cpu.c b/kernel/cpu.c
index d5c0998..6bbe261 100644 (file)
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -46,7 +46,8 @@
  * @bringup:   Single callback bringup or teardown selector
  * @cb_state:  The state for a single callback (install/uninstall)
  * @result:    Result of the operation
- * @done:      Signal completion to the issuer of the task
+ * @done_up:   Signal completion to the issuer of the task for cpu-up
+ * @done_down: Signal completion to the issuer of the task for cpu-down
  */
 struct cpuhp_cpu_state {
        enum cpuhp_state        state;
@@ -61,7 +62,8 @@ struct cpuhp_cpu_state {
        struct hlist_node       *last;
        enum cpuhp_state        cb_state;
        int                     result;
-       struct completion       done;
+       struct completion       done_up;
+       struct completion       done_down;
 #endif
 };
 
@@ -130,14 +132,6 @@ static bool cpuhp_is_ap_state(enum cpuhp_state state)
        return state > CPUHP_BRINGUP_CPU && state != CPUHP_TEARDOWN_CPU;
 }
 
-/*
- * The former STARTING/DYING states, ran with IRQs disabled and must not fail.
- */
-static bool cpuhp_is_atomic_state(enum cpuhp_state state)
-{
-       return CPUHP_AP_IDLE_DEAD <= state && state < CPUHP_AP_ONLINE;
-}
-
 static struct cpuhp_step *cpuhp_get_step(enum cpuhp_state state)
 {
        struct cpuhp_step *sp;
@@ -232,6 +226,26 @@ err:
 }
 
 #ifdef CONFIG_SMP
+static inline void wait_for_ap_thread(struct cpuhp_cpu_state *st, bool bringup)
+{
+       struct completion *done = bringup ? &st->done_up : &st->done_down;
+       wait_for_completion(done);
+}
+
+static inline void complete_ap_thread(struct cpuhp_cpu_state *st, bool bringup)
+{
+       struct completion *done = bringup ? &st->done_up : &st->done_down;
+       complete(done);
+}
+
+/*
+ * The former STARTING/DYING states, ran with IRQs disabled and must not fail.
+ */
+static bool cpuhp_is_atomic_state(enum cpuhp_state state)
+{
+       return CPUHP_AP_IDLE_DEAD <= state && state < CPUHP_AP_ONLINE;
+}
+
 /* Serializes the updates to cpu_online_mask, cpu_present_mask */
 static DEFINE_MUTEX(cpu_add_remove_lock);
 bool cpuhp_tasks_frozen;
@@ -368,7 +382,7 @@ static void __cpuhp_kick_ap(struct cpuhp_cpu_state *st)
        smp_mb();
        st->should_run = true;
        wake_up_process(st->thread);
-       wait_for_completion(&st->done);
+       wait_for_ap_thread(st, st->bringup);
 }
 
 static int cpuhp_kick_ap(struct cpuhp_cpu_state *st, enum cpuhp_state target)
@@ -391,7 +405,7 @@ static int bringup_wait_for_ap(unsigned int cpu)
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
 
        /* Wait for the CPU to reach CPUHP_AP_ONLINE_IDLE */
-       wait_for_completion(&st->done);
+       wait_for_ap_thread(st, true);
        if (WARN_ON_ONCE((!cpu_online(cpu))))
                return -ECANCELED;
 
@@ -464,7 +478,8 @@ static void cpuhp_create(unsigned int cpu)
 {
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
 
-       init_completion(&st->done);
+       init_completion(&st->done_up);
+       init_completion(&st->done_down);
 }
 
 static int cpuhp_should_run(unsigned int cpu)
@@ -557,7 +572,7 @@ next:
        cpuhp_lock_release(bringup);
 
        if (!st->should_run)
-               complete(&st->done);
+               complete_ap_thread(st, bringup);
 }
 
 /* Invoke a single callback on a remote cpu */
@@ -753,7 +768,7 @@ static int takedown_cpu(unsigned int cpu)
         *
         * Wait for the stop thread to go away.
         */
-       wait_for_completion(&st->done);
+       wait_for_ap_thread(st, false);
        BUG_ON(st->state != CPUHP_AP_IDLE_DEAD);
 
        /* Interrupts are moved away from the dying cpu, reenable alloc/free */
@@ -772,7 +787,7 @@ static void cpuhp_complete_idle_dead(void *arg)
 {
        struct cpuhp_cpu_state *st = arg;
 
-       complete(&st->done);
+       complete_ap_thread(st, false);
 }
 
 void cpuhp_report_idle_dead(void)
@@ -939,7 +954,7 @@ void cpuhp_online_idle(enum cpuhp_state state)
                return;
 
        st->state = CPUHP_AP_ONLINE_IDLE;
-       complete(&st->done);
+       complete_ap_thread(st, true);
 }
 
 /* Requires cpu_add_remove_lock to be held */