avoid deadlock by sequential iter and collecting then par iter

beacon_node/operation_pool/src/lib.rs

@@ -259,7 +259,7 @@ impl<T: EthSpec> OperationPool<T> {
             return Ok(vec![]);
         };
         let mut cliques_from_aggregates: Vec<_> = aggregate_attestations
-            .into_par_iter()
+            .iter()
             .filter(|(data, _)| {
                 data.slot + spec.min_attestation_inclusion_delay <= state.slot()
                     && state.slot() <= data.slot + T::slots_per_epoch()
@@ -272,6 +272,8 @@ impl<T: EthSpec> OperationPool<T> {
                 num_valid.fetch_add(aggregates.len(), Ordering::Relaxed);
                 (data, aggregates)
             })
+            .collect::<Vec<_>>()
+            .into_par_iter()
             .map(|(data, mut aggregates)| {
                 // Take the N aggregates with the highest number of set bits
                 // This is needed to avoid the bron_kerbosch algorithm generating millions of