ubifs: read-only if LEB may always be taken in ubifs_garbage_collect

If ubifs_garbage_collect_leb() returns -EAGAIN and ubifs_return_leb
returns error, a LEB will always has a "taken" flag. In this case,
set the ubifs to read-only to prevent a worse situation.
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/ubifs/gc.c

@@ -756,8 +756,17 @@ int ubifs_garbage_collect(struct ubifs_info *c, int anyway)
 				 * caller instead of the original '-EAGAIN'.
 				 */
 				err = ubifs_return_leb(c, lp.lnum);
-				if (err)
+				if (err) {
 					ret = err;
+					/*
+					 * An LEB may always be "taken",
+					 * so setting ubifs to read-only,
+					 * and then executing sync wbuf will
+					 * return -EROFS and enter the "out"
+					 * error branch.
+					 */
+					ubifs_ro_mode(c, ret);
+				}
 				/*  Maybe double return LEB if goto out */
 				lp.lnum = -1;
 				break;