After used bitmap freeng s->used_bmap points to the freed memory. If we try
to free used bitmap one more time it leads to double free error.

Set s->used_bmap to NULL to exclude double free error.

Signed-off-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
Reviewed-by: Denis V. Lunev <den@openvz.org>
---
 block/parallels.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/block/parallels.c b/block/parallels.c
index 9205a0864f..072b1efd78 100644
--- a/block/parallels.c
+++ b/block/parallels.c
@@ -245,6 +245,7 @@ static void parallels_free_used_bitmap(BlockDriverState *bs)
     BDRVParallelsState *s = bs->opaque;
     s->used_bmap_size = 0;
     g_free(s->used_bmap);
+    s->used_bmap = NULL;
 }
 
 static int64_t coroutine_fn GRAPH_RDLOCK
-- 
2.40.1