NFSv4: Fix a race in nfs_inode_reclaim_delegation()

If we race with a delegreturn before taking the spin lock, we
currently end up dropping the delegation stateid.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Tested-by: NOleg Drokin <green@linuxhacker.ru>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/delegation.c

@@ -195,15 +195,13 @@ void nfs_inode_reclaim_delegation(struct inode *inode, struct rpc_cred *cred,
 			rcu_read_unlock();
 			put_rpccred(oldcred);
 			trace_nfs4_reclaim_delegation(inode, res->delegation_type);
-		} else {
+			return;
+		}
 		/* We appear to have raced with a delegation return. */
 		spin_unlock(&delegation->lock);
-			rcu_read_unlock();
-			nfs_inode_set_delegation(inode, cred, res);
 	}
-	} else {
 	rcu_read_unlock();
-	}
+	nfs_inode_set_delegation(inode, cred, res);
 }
 
 static int nfs_do_return_delegation(struct inode *inode, struct nfs_delegation *delegation, int issync)