Merge pull request #39 from paritytech/bkchr-safety-violation

Don't finalize the same block multiple times

cumulus/consensus/src/lib.rs

@@ -131,6 +131,8 @@ where
 	type Block = Block;
 
 	fn finalize(&self, hash: <Self::Block as BlockT>::Hash) -> ClientResult<bool> {
+		// don't finalize the same block multiple times.
+		if self.chain_info().finalized_hash != hash {
 			match self.finalize_block(BlockId::hash(hash), None, true) {
 				Ok(()) => Ok(true),
 				Err(e) => match e {
@@ -138,6 +140,9 @@ where
 					_ => Err(e),
 				},
 			}
+		} else {
+			Ok(true)
+		}
 	}
 }