drivers/md/dm-ioctl.c: use kvmalloc rather than opencoded variant

copy_params uses kmalloc with vmalloc fallback.  We already have a
helper for that - kvmalloc.  This caller requires GFP_NOIO semantic so
it hasn't been converted with many others by previous patches.  All we
need to achieve this semantic is to use the scope
memalloc_noio_{save,restore} around kvmalloc.

Link: http://lkml.kernel.org/r/20170306103327.2766-4-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/md/dm-ioctl.c

@@ -1691,6 +1691,7 @@ static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl *param_kern
 	struct dm_ioctl *dmi;
 	int secure_data;
 	const size_t minimum_data_size = offsetof(struct dm_ioctl, data);
+	unsigned noio_flag;
 
 	if (copy_from_user(param_kernel, user, minimum_data_size))
 		return -EFAULT;
@@ -1713,15 +1714,9 @@ static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl *param_kern
 	 * Use kmalloc() rather than vmalloc() when we can.
 	 */
 	dmi = NULL;
-	if (param_kernel->data_size <= KMALLOC_MAX_SIZE)
-		dmi = kmalloc(param_kernel->data_size, GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
-
-	if (!dmi) {
-		unsigned noio_flag;
-		noio_flag = memalloc_noio_save();
-		dmi = __vmalloc(param_kernel->data_size, GFP_NOIO | __GFP_HIGH | __GFP_HIGHMEM, PAGE_KERNEL);
-		memalloc_noio_restore(noio_flag);
-	}
+	noio_flag = memalloc_noio_save();
+	dmi = kvmalloc(param_kernel->data_size, GFP_KERNEL);
+	memalloc_noio_restore(noio_flag);
 
 	if (!dmi) {
 		if (secure_data && clear_user(user, param_kernel->data_size))