Merge branch 'netpoll-make-sure-napi_list-is-safe-for-RCU-traversal'

Jakub Kicinski says:

====================
netpoll: make sure napi_list is safe for RCU traversal

This series is a follow-up to the fix in commit 96e97bc0 ("net:
disable netpoll on fresh napis"). To avoid any latent race conditions
convert dev->napi_list to a proper RCU list. We need minor restructuring
because it looks like netif_napi_del() used to be idempotent, and
it may be quite hard to track down everyone who depends on that.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bnx2x/bnx2x_cmn.h

@@ -825,9 +825,9 @@ static inline void bnx2x_del_all_napi_cnic(struct bnx2x *bp)
 	int i;
 
 	for_each_rx_queue_cnic(bp, i) {
-		napi_hash_del(&bnx2x_fp(bp, i, napi));
-		netif_napi_del(&bnx2x_fp(bp, i, napi));
+		__netif_napi_del(&bnx2x_fp(bp, i, napi));
 	}
+	synchronize_net();
 }
 
 static inline void bnx2x_del_all_napi(struct bnx2x *bp)
@@ -835,9 +835,9 @@ static inline void bnx2x_del_all_napi(struct bnx2x *bp)
 	int i;
 
 	for_each_eth_queue(bp, i) {
-		napi_hash_del(&bnx2x_fp(bp, i, napi));
-		netif_napi_del(&bnx2x_fp(bp, i, napi));
+		__netif_napi_del(&bnx2x_fp(bp, i, napi));
 	}
+	synchronize_net();
 }
 
 int bnx2x_set_int_mode(struct bnx2x *bp);

drivers/net/ethernet/broadcom/bnxt/bnxt.c

@@ -8634,10 +8634,9 @@ static void bnxt_del_napi(struct bnxt *bp)
 	for (i = 0; i < bp->cp_nr_rings; i++) {
 		struct bnxt_napi *bnapi = bp->bnapi[i];
 
-		napi_hash_del(&bnapi->napi);
-		netif_napi_del(&bnapi->napi);
+		__netif_napi_del(&bnapi->napi);
 	}
-	/* We called napi_hash_del() before netif_napi_del(), we need
+	/* We called __netif_napi_del(), we need
 	 * to respect an RCU grace period before freeing napi structures.
 	 */
 	synchronize_net();

drivers/net/ethernet/cisco/enic/enic_main.c

@@ -2529,13 +2529,15 @@ static void enic_dev_deinit(struct enic *enic)
 {
 	unsigned int i;
 
-	for (i = 0; i < enic->rq_count; i++) {
-		napi_hash_del(&enic->napi[i]);
-		netif_napi_del(&enic->napi[i]);
-	}
+	for (i = 0; i < enic->rq_count; i++)
+		__netif_napi_del(&enic->napi[i]);
+
 	if (vnic_dev_get_intr_mode(enic->vdev) == VNIC_DEV_INTR_MODE_MSIX)
 		for (i = 0; i < enic->wq_count; i++)
-			netif_napi_del(&enic->napi[enic_cq_wq(enic, i)]);
+			__netif_napi_del(&enic->napi[enic_cq_wq(enic, i)]);
+
+	/* observe RCU grace period after __netif_napi_del() calls */
+	synchronize_net();
 
 	enic_free_vnic_resources(enic);
 	enic_clear_intr_mode(enic);

drivers/net/ethernet/intel/ixgbe/ixgbe_lib.c

@@ -1029,10 +1029,10 @@ static void ixgbe_free_q_vector(struct ixgbe_adapter *adapter, int v_idx)
 		WRITE_ONCE(adapter->rx_ring[ring->queue_index], NULL);
 
 	adapter->q_vector[v_idx] = NULL;
-	napi_hash_del(&q_vector->napi);
-	netif_napi_del(&q_vector->napi);
+	__netif_napi_del(&q_vector->napi);
 
 	/*
+	 * after a call to __netif_napi_del() napi may still be used and
 	 * ixgbe_get_stats64() might access the rings on this vector,
 	 * we must wait a grace period before freeing it.
 	 */

drivers/net/ethernet/myricom/myri10ge/myri10ge.c

@@ -3543,11 +3543,10 @@ static void myri10ge_free_slices(struct myri10ge_priv *mgp)
 					  ss->fw_stats, ss->fw_stats_bus);
 			ss->fw_stats = NULL;
 		}
-		napi_hash_del(&ss->napi);
-		netif_napi_del(&ss->napi);
+		__netif_napi_del(&ss->napi);
 	}
 	/* Wait till napi structs are no longer used, and then free ss. */
-	synchronize_rcu();
+	synchronize_net();
 	kfree(mgp->ss);
 	mgp->ss = NULL;
 }

drivers/net/veth.c

@@ -897,14 +897,13 @@ static void veth_napi_del(struct net_device *dev)
 		struct veth_rq *rq = &priv->rq[i];
 
 		napi_disable(&rq->xdp_napi);
-		napi_hash_del(&rq->xdp_napi);
+		__netif_napi_del(&rq->xdp_napi);
 	}
 	synchronize_net();
 
 	for (i = 0; i < dev->real_num_rx_queues; i++) {
 		struct veth_rq *rq = &priv->rq[i];
 
-		netif_napi_del(&rq->xdp_napi);
 		rq->rx_notify_masked = false;
 		ptr_ring_cleanup(&rq->xdp_ring, veth_ptr_free);
 	}

drivers/net/virtio_net.c

@@ -2604,12 +2604,11 @@ static void virtnet_free_queues(struct virtnet_info *vi)
 	int i;
 
 	for (i = 0; i < vi->max_queue_pairs; i++) {
-		napi_hash_del(&vi->rq[i].napi);
-		netif_napi_del(&vi->rq[i].napi);
-		netif_napi_del(&vi->sq[i].napi);
+		__netif_napi_del(&vi->rq[i].napi);
+		__netif_napi_del(&vi->sq[i].napi);
 	}
 
-	/* We called napi_hash_del() before netif_napi_del(),
+	/* We called __netif_napi_del(),
 	 * we need to respect an RCU grace period before freeing vi->rq
 	 */
 	synchronize_net();

include/linux/netdevice.h

@@ -70,6 +70,7 @@ struct udp_tunnel_nic;
 struct bpf_prog;
 struct xdp_buff;
 
+void synchronize_net(void);
 void netdev_set_default_ethtool_ops(struct net_device *dev,
 				    const struct ethtool_ops *ops);
 
@@ -354,7 +355,7 @@ enum {
 	NAPI_STATE_MISSED,	/* reschedule a napi */
 	NAPI_STATE_DISABLE,	/* Disable pending */
 	NAPI_STATE_NPSVC,	/* Netpoll - don't dequeue from poll_list */
-	NAPI_STATE_HASHED,	/* In NAPI hash (busy polling possible) */
+	NAPI_STATE_LISTED,	/* NAPI added to system lists */
 	NAPI_STATE_NO_BUSY_POLL,/* Do not add in napi_hash, no busy polling */
 	NAPI_STATE_IN_BUSY_POLL,/* sk_busy_loop() owns this NAPI */
 };
@@ -364,7 +365,7 @@ enum {
 	NAPIF_STATE_MISSED	 = BIT(NAPI_STATE_MISSED),
 	NAPIF_STATE_DISABLE	 = BIT(NAPI_STATE_DISABLE),
 	NAPIF_STATE_NPSVC	 = BIT(NAPI_STATE_NPSVC),
-	NAPIF_STATE_HASHED	 = BIT(NAPI_STATE_HASHED),
+	NAPIF_STATE_LISTED	 = BIT(NAPI_STATE_LISTED),
 	NAPIF_STATE_NO_BUSY_POLL = BIT(NAPI_STATE_NO_BUSY_POLL),
 	NAPIF_STATE_IN_BUSY_POLL = BIT(NAPI_STATE_IN_BUSY_POLL),
 };
@@ -488,20 +489,6 @@ static inline bool napi_complete(struct napi_struct *n)
 	return napi_complete_done(n, 0);
 }
 
-/**
- *	napi_hash_del - remove a NAPI from global table
- *	@napi: NAPI context
- *
- * Warning: caller must observe RCU grace period
- * before freeing memory containing @napi, if
- * this function returns true.
- * Note: core networking stack automatically calls it
- * from netif_napi_del().
- * Drivers might want to call this helper to combine all
- * the needed RCU grace periods into a single one.
- */
-bool napi_hash_del(struct napi_struct *napi);
-
 /**
  *	napi_disable - prevent NAPI from scheduling
  *	@n: NAPI context
@@ -2367,13 +2354,27 @@ static inline void netif_tx_napi_add(struct net_device *dev,
 	netif_napi_add(dev, napi, poll, weight);
 }
 
+/**
+ *  __netif_napi_del - remove a NAPI context
+ *  @napi: NAPI context
+ *
+ * Warning: caller must observe RCU grace period before freeing memory
+ * containing @napi. Drivers might want to call this helper to combine
+ * all the needed RCU grace periods into a single one.
+ */
+void __netif_napi_del(struct napi_struct *napi);
+
 /**
  *  netif_napi_del - remove a NAPI context
  *  @napi: NAPI context
  *
  *  netif_napi_del() removes a NAPI context from the network device NAPI list
  */
-void netif_napi_del(struct napi_struct *napi);
+static inline void netif_napi_del(struct napi_struct *napi)
+{
+	__netif_napi_del(napi);
+	synchronize_net();
+}
 
 struct napi_gro_cb {
 	/* Virtual address of skb_shinfo(skb)->frags[0].page + offset. */
@@ -2797,7 +2798,6 @@ static inline void unregister_netdevice(struct net_device *dev)
 int netdev_refcnt_read(const struct net_device *dev);
 void free_netdev(struct net_device *dev);
 void netdev_freemem(struct net_device *dev);
-void synchronize_net(void);
 int init_dummy_netdev(struct net_device *dev);
 
 struct net_device *netdev_get_xmit_slave(struct net_device *dev,

net/core/dev.c

@@ -6533,8 +6533,7 @@ EXPORT_SYMBOL(napi_busy_loop);
 
 static void napi_hash_add(struct napi_struct *napi)
 {
-	if (test_bit(NAPI_STATE_NO_BUSY_POLL, &napi->state) ||
-	    test_and_set_bit(NAPI_STATE_HASHED, &napi->state))
+	if (test_bit(NAPI_STATE_NO_BUSY_POLL, &napi->state))
 		return;
 
 	spin_lock(&napi_hash_lock);
@@ -6555,20 +6554,14 @@ static void napi_hash_add(struct napi_struct *napi)
 /* Warning : caller is responsible to make sure rcu grace period
  * is respected before freeing memory containing @napi
  */
-bool napi_hash_del(struct napi_struct *napi)
+static void napi_hash_del(struct napi_struct *napi)
 {
-	bool rcu_sync_needed = false;
-
 	spin_lock(&napi_hash_lock);
 
-	if (test_and_clear_bit(NAPI_STATE_HASHED, &napi->state)) {
-		rcu_sync_needed = true;
-		hlist_del_rcu(&napi->napi_hash_node);
-	}
+	hlist_del_init_rcu(&napi->napi_hash_node);
+
 	spin_unlock(&napi_hash_lock);
-	return rcu_sync_needed;
 }
-EXPORT_SYMBOL_GPL(napi_hash_del);
 
 static enum hrtimer_restart napi_watchdog(struct hrtimer *timer)
 {
@@ -6600,7 +6593,11 @@ static void init_gro_hash(struct napi_struct *napi)
 void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
 		    int (*poll)(struct napi_struct *, int), int weight)
 {
+	if (WARN_ON(test_and_set_bit(NAPI_STATE_LISTED, &napi->state)))
+		return;
+
 	INIT_LIST_HEAD(&napi->poll_list);
+	INIT_HLIST_NODE(&napi->napi_hash_node);
 	hrtimer_init(&napi->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_PINNED);
 	napi->timer.function = napi_watchdog;
 	init_gro_hash(napi);
@@ -6653,18 +6650,19 @@ static void flush_gro_hash(struct napi_struct *napi)
 }
 
 /* Must be called in process context */
-void netif_napi_del(struct napi_struct *napi)
+void __netif_napi_del(struct napi_struct *napi)
 {
-	might_sleep();
-	if (napi_hash_del(napi))
-		synchronize_net();
-	list_del_init(&napi->dev_list);
+	if (!test_and_clear_bit(NAPI_STATE_LISTED, &napi->state))
+		return;
+
+	napi_hash_del(napi);
+	list_del_rcu(&napi->dev_list);
 	napi_free_frags(napi);
 
 	flush_gro_hash(napi);
 	napi->gro_bitmask = 0;
 }
-EXPORT_SYMBOL(netif_napi_del);
+EXPORT_SYMBOL(__netif_napi_del);
 
 static int napi_poll(struct napi_struct *n, struct list_head *repoll)
 {

net/core/netpoll.c

@@ -297,7 +297,7 @@ static int netpoll_owner_active(struct net_device *dev)
 {
 	struct napi_struct *napi;
 
-	list_for_each_entry(napi, &dev->napi_list, dev_list) {
+	list_for_each_entry_rcu(napi, &dev->napi_list, dev_list) {
 		if (napi->poll_owner == smp_processor_id())
 			return 1;
 	}