f2fs: don't issue discard commands in online discard is on

Actually, we don't need to issue discard commands, if discard is on, as
mentioned in the comment.
Reviewed-by: NChao Yu <yuchao0@huawei.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -2469,23 +2469,24 @@ int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range)
 	if (err)
 		goto out;
 
-	start_block = START_BLOCK(sbi, start_segno);
-	end_block = START_BLOCK(sbi, end_segno + 1);
-
-	__init_discard_policy(sbi, &dpolicy, DPOLICY_FSTRIM, cpc.trim_minlen);
-	__issue_discard_cmd_range(sbi, &dpolicy, start_block, end_block);
-
 	/*
 	 * We filed discard candidates, but actually we don't need to wait for
 	 * all of them, since they'll be issued in idle time along with runtime
 	 * discard option. User configuration looks like using runtime discard
 	 * or periodic fstrim instead of it.
 	 */
-	if (!test_opt(sbi, DISCARD)) {
+	if (test_opt(sbi, DISCARD))
+		goto out;
+
+	start_block = START_BLOCK(sbi, start_segno);
+	end_block = START_BLOCK(sbi, end_segno + 1);
+
+	__init_discard_policy(sbi, &dpolicy, DPOLICY_FSTRIM, cpc.trim_minlen);
+	__issue_discard_cmd_range(sbi, &dpolicy, start_block, end_block);
+
 	trimmed = __wait_discard_cmd_range(sbi, &dpolicy,
 					start_block, end_block);
 	range->len = F2FS_BLK_TO_BYTES(trimmed);
-	}
 out:
 	return err;
 }