dm-flakey: error all IOs when num_features is absent

dm-flakey would error all IOs if num_features was 0, but if it was
absent, dm-flakey would never error any IO. Fix this so that no
num_features works the same as num_features set to 0.

Fixes: aa7d7bc ("dm flakey: add an "error_reads" option")
Reported-by: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

Author: bmarzins

drivers/md/dm-flakey.c

@@ -53,8 +53,8 @@ struct per_bio_data {
 static int parse_features(struct dm_arg_set *as, struct flakey_c *fc,
 			  struct dm_target *ti)
 {
-	int r;
-	unsigned int argc;
+	int r = 0;
+	unsigned int argc = 0;
 	const char *arg_name;
 
 	static const struct dm_arg _args[] = {
@@ -65,14 +65,13 @@ static int parse_features(struct dm_arg_set *as, struct flakey_c *fc,
 		{0, PROBABILITY_BASE, "Invalid random corrupt argument"},
 	};
 
-	/* No feature arguments supplied. */
-	if (!as->argc)
-		return 0;
-
-	r = dm_read_arg_group(_args, as, &argc, &ti->error);
-	if (r)
+	if (as->argc && (r = dm_read_arg_group(_args, as, &argc, &ti->error)))
 		return r;
 
+	/* No feature arguments supplied. */
+	if (!argc)
+		goto error_all_io;
+
 	while (argc) {
 		arg_name = dm_shift_arg(as);
 		argc--;
@@ -232,6 +231,7 @@ static int parse_features(struct dm_arg_set *as, struct flakey_c *fc,
 	if (!fc->corrupt_bio_byte && !test_bit(ERROR_READS, &fc->flags) &&
 	    !test_bit(DROP_WRITES, &fc->flags) && !test_bit(ERROR_WRITES, &fc->flags) &&
 	    !fc->random_read_corrupt && !fc->random_write_corrupt) {
+error_all_io:
 		set_bit(ERROR_WRITES, &fc->flags);
 		set_bit(ERROR_READS, &fc->flags);
 	}