Make xattr dir truncate and remove in one tx

We need truncate and remove be in the same tx when doing zfs_rmnode on xattr
dir. Otherwise, if we truncate and crash, we'll end up with inconsistent zap
object on the delete queue. We do this by skipping dmu_free_long_range and let
zfs_znode_delete to do the work.

Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #4114
Issue #4052
Issue #4006
Issue #3018
Issue #2861

Author: tuxoko

module/zfs/zfs_dir.c

@@ -632,15 +632,22 @@ zfs_rmnode(znode_t *zp)
 	}
 
 	/*
-	 * Free up all the data in the file.
+	 * Free up all the data in the file.  We don't do this for directories
+	 * because we need truncate and remove to be in the same tx, like in
+	 * zfs_znode_delete(). Otherwise, if we crash here we'll end up with
+	 * an inconsistent truncated zap object in the delete queue.  Note a
+	 * truncated file is harmless since it only contains user data.
 	 */
-	error = dmu_free_long_range(os, zp->z_id, 0, DMU_OBJECT_END);
-	if (error) {
-		/*
-		 * Not enough space.  Leave the file in the unlinked set.
-		 */
-		zfs_znode_dmu_fini(zp);
-		return;
+	if (S_ISREG(ZTOI(zp)->i_mode)) {
+		error = dmu_free_long_range(os, zp->z_id, 0, DMU_OBJECT_END);
+		if (error) {
+			/*
+			 * Not enough space.  Leave the file in the unlinked
+			 * set.
+			 */
+			zfs_znode_dmu_fini(zp);
+			return;
+		}
 	}
 
 	/*