firmware: arm_sdei: fix double-lock on hibernate with shared events

SDEI has private events that must be registered on each CPU. When
CPUs come and go they must re-register and re-enable their private
events. Each event has flags to indicate whether this should happen
to protect against an event being registered on a CPU coming online,
while all the others are unregistering the event.

These flags are protected by the sdei_list_lock spinlock, because
the cpuhp callbacks can't take the mutex.

Hibernate needs to unregister all events, but keep the in-memory
re-register and re-enable as they are. sdei_unregister_shared()
takes the spinlock to walk the list, then calls _sdei_event_unregister()
on each shared event. _sdei_event_unregister() tries to take the
same spinlock to update re-register and re-enable. This doesn't go
so well.

Push the re-register and re-enable updates out to their callers.
sdei_unregister_shared() doesn't want these values updated, so
doesn't need to do anything.

This also fixes shared events getting lost over hibernate as this
path made them look unregistered.

Fixes: da351827 ("firmware: arm_sdei: Add support for CPU and system power states")
Reported-by: Liguang Zhang <zhangliguang@linux.alibaba.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

drivers/firmware/arm_sdei.c

@@ -491,11 +491,6 @@ static int _sdei_event_unregister(struct sdei_event *event)
 {
 	lockdep_assert_held(&sdei_events_lock);
 
-	spin_lock(&sdei_list_lock);
-	event->reregister = false;
-	event->reenable = false;
-	spin_unlock(&sdei_list_lock);
-
 	if (event->type == SDEI_EVENT_TYPE_SHARED)
 		return sdei_api_event_unregister(event->event_num);
 
@@ -518,6 +513,11 @@ int sdei_event_unregister(u32 event_num)
 			break;
 		}
 
+		spin_lock(&sdei_list_lock);
+		event->reregister = false;
+		event->reenable = false;
+		spin_unlock(&sdei_list_lock);
+
 		err = _sdei_event_unregister(event);
 		if (err)
 			break;
@@ -585,26 +585,15 @@ static int _sdei_event_register(struct sdei_event *event)
 
 	lockdep_assert_held(&sdei_events_lock);
 
-	spin_lock(&sdei_list_lock);
-	event->reregister = true;
-	spin_unlock(&sdei_list_lock);
-
 	if (event->type == SDEI_EVENT_TYPE_SHARED)
 		return sdei_api_event_register(event->event_num,
 					       sdei_entry_point,
 					       event->registered,
 					       SDEI_EVENT_REGISTER_RM_ANY, 0);
 
-
 	err = sdei_do_cross_call(_local_event_register, event);
-	if (err) {
-		spin_lock(&sdei_list_lock);
-		event->reregister = false;
-		event->reenable = false;
-		spin_unlock(&sdei_list_lock);
-
+	if (err)
 		sdei_do_cross_call(_local_event_unregister, event);
-	}
 
 	return err;
 }
@@ -632,8 +621,17 @@ int sdei_event_register(u32 event_num, sdei_event_callback *cb, void *arg)
 			break;
 		}
 
+		spin_lock(&sdei_list_lock);
+		event->reregister = true;
+		spin_unlock(&sdei_list_lock);
+
 		err = _sdei_event_register(event);
 		if (err) {
+			spin_lock(&sdei_list_lock);
+			event->reregister = false;
+			event->reenable = false;
+			spin_unlock(&sdei_list_lock);
+
 			sdei_event_destroy(event);
 			pr_warn("Failed to register event %u: %d\n", event_num,
 				err);