lightnvm: add check after mempool allocation

The mempool allocation might fail. Make sure to return error when it
does, instead of causing a kernel panic.

Signed-off-by: Javier Gonzalez <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/drivers/lightnvm/rrpc.c b/drivers/lightnvm/rrpc.c
index a1e7488..f4bc986 100644
--- a/drivers/lightnvm/rrpc.c
+++ b/drivers/lightnvm/rrpc.c
@@ -287,6 +287,8 @@
 	}
 
 	page = mempool_alloc(rrpc->page_pool, GFP_NOIO);
+	if (!page)
+		return -ENOMEM;
 
 	while ((slot = find_first_zero_bit(rblk->invalid_pages,
 					    nr_pgs_per_blk)) < nr_pgs_per_blk) {