Revert "xsk: Fix race condition in AF_XDP generic RX path"

This reverts commit 65d3c57061 which is
commit a1356ac7749cafc4e27aa62c0c4604b5dca4983e upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I15acb18ebd9dd5a0d2fb0bf4153c5ced269f978a
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

include/net/xdp_sock.h

@@ -71,6 +71,9 @@ struct xdp_sock {
 	 */
 	u32 tx_budget_spent;
 
+	/* Protects generic receive. */
+	spinlock_t rx_lock;
+
 	/* Statistics */
 	u64 rx_dropped;
 	u64 rx_queue_full;

include/net/xsk_buff_pool.h

@@ -55,8 +55,6 @@ struct xsk_buff_pool {
 	refcount_t users;
 	struct xdp_umem *umem;
 	struct work_struct work;
-	/* Protects generic receive in shared and non-shared umem mode. */
-	spinlock_t rx_lock;
 	struct list_head free_list;
 	struct list_head xskb_list;
 	u32 heads_cnt;

net/xdp/xsk.c

@@ -338,14 +338,13 @@ int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
 	u32 len = xdp_get_buff_len(xdp);
 	int err;
 
+	spin_lock_bh(&xs->rx_lock);
 	err = xsk_rcv_check(xs, xdp, len);
 	if (!err) {
-		spin_lock_bh(&xs->pool->rx_lock);
 		err = __xsk_rcv(xs, xdp, len);
 		xsk_flush(xs);
-		spin_unlock_bh(&xs->pool->rx_lock);
 	}
-
+	spin_unlock_bh(&xs->rx_lock);
 	return err;
 }
 
@@ -1721,6 +1720,7 @@ static int xsk_create(struct net *net, struct socket *sock, int protocol,
 	xs = xdp_sk(sk);
 	xs->state = XSK_READY;
 	mutex_init(&xs->mutex);
+	spin_lock_init(&xs->rx_lock);
 
 	INIT_LIST_HEAD(&xs->map_list);
 	spin_lock_init(&xs->map_list_lock);

net/xdp/xsk_buff_pool.c

@@ -87,7 +87,6 @@ struct xsk_buff_pool *xp_create_and_assign_umem(struct xdp_sock *xs,
 	pool->addrs = umem->addrs;
 	pool->tx_metadata_len = umem->tx_metadata_len;
 	pool->tx_sw_csum = umem->flags & XDP_UMEM_TX_SW_CSUM;
-	spin_lock_init(&pool->rx_lock);
 	INIT_LIST_HEAD(&pool->free_list);
 	INIT_LIST_HEAD(&pool->xskb_list);
 	INIT_LIST_HEAD(&pool->xsk_tx_list);