bpf, devmap: Use GFP_KERNEL for xdp bulk queue allocation

The devmap bulk queue is allocated with GFP_ATOMIC and the allocation
may fail if there is no available space in existing percpu pool.

Since commit 75ccae62 ("xdp: Move devmap bulk queue into struct net_device")
moved the bulk queue allocation to NETDEV_REGISTER callback, whose context
is allowed to sleep, use GFP_KERNEL instead of GFP_ATOMIC to let percpu
allocator extend the pool when needed and avoid possible failure of netdev
registration.

As the required alignment is natural, we can simply use alloc_percpu().

Fixes: 75ccae62 ("xdp: Move devmap bulk queue into struct net_device")
Signed-off-by: Jun'ichi Nomura <junichi.nomura@nec.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20210209082451.GA44021@jeru.linux.bs1.fc.nec.co.jp

kernel/bpf/devmap.c

@@ -802,9 +802,7 @@ static int dev_map_notification(struct notifier_block *notifier,
 			break;
 
 		/* will be freed in free_netdev() */
-		netdev->xdp_bulkq =
-			__alloc_percpu_gfp(sizeof(struct xdp_dev_bulk_queue),
-					   sizeof(void *), GFP_ATOMIC);
+		netdev->xdp_bulkq = alloc_percpu(struct xdp_dev_bulk_queue);
 		if (!netdev->xdp_bulkq)
 			return NOTIFY_BAD;