drbd: Null pointer deref fix to the large "multi bio rewrite"

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 461d9872d4d3..bc9ab7fb2cc7 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -98,6 +98,10 @@ static struct page *page_chain_del(struct page **head, int n)
         BUG_ON(!head);
 
         page = *head;
+
+        if (!page)
+                return NULL;
+
         while (page) {
                 tmp = page_chain_next(page);
                 if (--n == 0)