UBI: Fix double free after do_sync_erase()

If the erase worker is unable to erase a PEB it will
free the ubi_wl_entry itself.
The failing ubi_wl_entry must not free()'d again after
do_sync_erase() returns.

Cc: <stable@vger.kernel.org>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

drivers/mtd/ubi/wl.c

@@ -1216,7 +1216,6 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
 
 	err = do_sync_erase(ubi, e1, vol_id, lnum, 0);
 	if (err) {
-		kmem_cache_free(ubi_wl_entry_slab, e1);
 		if (e2)
 			kmem_cache_free(ubi_wl_entry_slab, e2);
 		goto out_ro;
@@ -1230,10 +1229,8 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
 		dbg_wl("PEB %d (LEB %d:%d) was put meanwhile, erase",
 		       e2->pnum, vol_id, lnum);
 		err = do_sync_erase(ubi, e2, vol_id, lnum, 0);
-		if (err) {
-			kmem_cache_free(ubi_wl_entry_slab, e2);
+		if (err)
 			goto out_ro;
-		}
 	}
 
 	dbg_wl("done");
@@ -1269,10 +1266,9 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
 
 	ubi_free_vid_hdr(ubi, vid_hdr);
 	err = do_sync_erase(ubi, e2, vol_id, lnum, torture);
-	if (err) {
-		kmem_cache_free(ubi_wl_entry_slab, e2);
+	if (err)
 		goto out_ro;
-	}
+
 	mutex_unlock(&ubi->move_mutex);
 	return 0;