block-map: add __GFP_ZERO flag for alloc_page in function bio_copy_kern

Add __GFP_ZERO flag for alloc_page in function bio_copy_kern to initialize
the buffer of a bio.

Signed-off-by: Haimin Zhang <tcs.kernel@gmail.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220216084038.15635-1-tcs.kernel@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Haimin Zhang

block/blk-map.c

@@ -446,7 +446,7 @@ static struct bio *bio_copy_kern(struct request_queue *q, void *data,
 		if (bytes > len)
 			bytes = len;
 
-		page = alloc_page(GFP_NOIO | gfp_mask);
+		page = alloc_page(GFP_NOIO | __GFP_ZERO | gfp_mask);
 		if (!page)
 			goto cleanup;