UBIFS: allow for sync_fs when read-only

sync_fs can be called even if the file system is mounted
read-only.  Ensure the commit is not run in that case.
Reported-by: NZoltan Sogor <weth@inf.u-szeged.hu>
Signed-off-by: NAdrian Hunter <ext-adrian.hunter@nokia.com>

fs/ubifs/super.c

@@ -420,21 +420,22 @@ static int ubifs_sync_fs(struct super_block *sb, int wait)
 	int i, ret = 0, err;
 	long long bud_bytes;
 
-	if (c->jheads)
+	if (c->jheads) {
 		for (i = 0; i < c->jhead_cnt; i++) {
 			err = ubifs_wbuf_sync(&c->jheads[i].wbuf);
 			if (err && !ret)
 				ret = err;
 		}
 
-	/* Commit the journal unless it has too few data */
-	spin_lock(&c->buds_lock);
-	bud_bytes = c->bud_bytes;
-	spin_unlock(&c->buds_lock);
-	if (bud_bytes > c->leb_size) {
-		err = ubifs_run_commit(c);
-		if (err)
-			return err;
+		/* Commit the journal unless it has too little data */
+		spin_lock(&c->buds_lock);
+		bud_bytes = c->bud_bytes;
+		spin_unlock(&c->buds_lock);
+		if (bud_bytes > c->leb_size) {
+			err = ubifs_run_commit(c);
+			if (err)
+				return err;
+		}
 	}
 
 	/*