Use read_recursive locks in database (#2417)

beacon_node/store/src/hot_cold_store.rs

@@ -759,7 +759,7 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> HotColdDB<E, Hot, Cold>
         let high_restore_point_idx = low_restore_point_idx + 1;
 
         // Acquire the read lock, so that the split can't change while this is happening.
-        let split = self.split.read();
+        let split = self.split.read_recursive();
 
         let low_restore_timer = metrics::start_timer(&metrics::LOAD_LOW_RESTORE_POINT_TIME);
         let low_restore_point = self.load_restore_point_by_index(low_restore_point_idx)?;
@@ -950,7 +950,7 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> HotColdDB<E, Hot, Cold>
 
     /// Fetch a copy of the current split slot from memory.
     pub fn get_split_slot(&self) -> Slot {
-        self.split.read().slot
+        self.split.read_recursive().slot
     }
 
     /// Fetch the slot of the most recently stored restore point.
@@ -1123,7 +1123,7 @@ pub fn migrate_database<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>>(
     // 0. Check that the migration is sensible.
     // The new frozen head must increase the current split slot, and lie on an epoch
     // boundary (in order for the hot state summary scheme to work).
-    let current_split_slot = store.split.read().slot;
+    let current_split_slot = store.split.read_recursive().slot;
 
     if frozen_head.slot() < current_split_slot {
         return Err(HotColdDBError::FreezeSlotError {