[PATCH 2/2] smp/hotplug,lockdep: Annotate cpuhp_state

[Peter Zijlstra]

After the st->done annotation, lockdep cross-release now complains
about:

  CPU0                  CPU1                    CPU2
  cpuhp_up_callbacks:	takedown_cpu:		cpuhp_thread_fun:

  cpuhp_state
                        irq_lock_sparse()
    irq_lock_sparse()
                        wait_for_completion()
                                                cpuhp_state
                                                complete()

which again spells deadlock, because CPU0 needs to wait for CPU1's
irq_lock_sparse which will wait for CPU2's completion, which in turn
waits for CPU0's cpuhp_state.

Now, this again mixes up and down chains, but now on cpuhp_state.

Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Byungchul Park <max.byungchul.park@xxxxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Reported-by: Mike Galbraith <efault@xxxxxx>
Tested-by: Mike Galbraith <efault@xxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 kernel/cpu.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -67,11 +67,14 @@ struct cpuhp_cpu_state {
 static DEFINE_PER_CPU(struct cpuhp_cpu_state, cpuhp_state);
 
 #if defined(CONFIG_LOCKDEP) && defined(CONFIG_SMP)
-static struct lock_class_key cpuhp_state_key;
+static struct lock_class_key cpuhp_state_up_key;
+#ifdef CONFIG_HOTPLUG_CPU
+static struct lock_class_key cpuhp_state_down_key;
+#endif
 static struct lockdep_map cpuhp_state_lock_map =
-	STATIC_LOCKDEP_MAP_INIT("cpuhp_state", &cpuhp_state_key);
+	STATIC_LOCKDEP_MAP_INIT("cpuhp_state-up", &cpuhp_state_up_key);
 #endif
 
 /**
  * cpuhp_step - Hotplug state machine step
  * @name:	Name of the step
@@ -714,6 +718,8 @@ static int __ref _cpu_down(unsigned int
 	cpus_write_lock();
 
 	lockdep_reinit_st_done();
+	lockdep_init_map(&cpuhp_state_lock_map, "cpuhp_state-down",
+			 &cpuhp_state_down_key, 0);
 
 	cpuhp_tasks_frozen = tasks_frozen;
 
@@ -828,6 +834,8 @@ static int _cpu_up(unsigned int cpu, int
 	cpus_write_lock();
 
 	lockdep_reinit_st_done();
+	lockdep_init_map(&cpuhp_state_lock_map, "cpuhp_state-up",
+			 &cpuhp_state_up_key, 0);
 
 	if (!cpu_present(cpu)) {
 		ret = -EINVAL;