Merge branch 'af_xdp-fixes'

Magnus Karlsson says:

====================
This patch set fixes three bugs in the SKB TX path of AF_XDP.
Details in the individual commits.

The structure of the patch set is as follows:

Patch 1: Fix for lost completion message
Patch 2-3: Fix for possible multiple completions of single packet
Patch 4: Fix potential race during error

Changes from v1:

* Added explanation of race in commit message of patch 4.
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

4 files changed, 14 insertions, 11 deletions

diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
index 9fe472f2ac95..7161856bcf9c 100644
--- a/include/net/xdp_sock.h
+++ b/include/net/xdp_sock.h
@@ -60,6 +60,10 @@ struct xdp_sock {
 	bool zc;
 	/* Protects multiple processes in the control path */
 	struct mutex mutex;
+	/* Mutual exclusion of NAPI TX thread and sendmsg error paths
+	 * in the SKB destructor callback.
+	 */
+	spinlock_t tx_completion_lock;
 	u64 rx_dropped;
 };
 
diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 59fb7d3c36a3..7d220cbd09b6 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -199,8 +199,11 @@ static void xsk_destruct_skb(struct sk_buff *skb)
 {
 	u64 addr = (u64)(long)skb_shinfo(skb)->destructor_arg;
 	struct xdp_sock *xs = xdp_sk(skb->sk);
+	unsigned long flags;
 
+	spin_lock_irqsave(&xs->tx_completion_lock, flags);
 	WARN_ON_ONCE(xskq_produce_addr(xs->umem->cq, addr));
+	spin_unlock_irqrestore(&xs->tx_completion_lock, flags);
 
 	sock_wfree(skb);
 }
@@ -268,15 +271,15 @@ static int xsk_generic_xmit(struct sock *sk, struct msghdr *m,
 		skb->destructor = xsk_destruct_skb;
 
 		err = dev_direct_xmit(skb, xs->queue_id);
+		xskq_discard_desc(xs->tx);
 		/* Ignore NET_XMIT_CN as packet might have been sent */
 		if (err == NET_XMIT_DROP || err == NETDEV_TX_BUSY) {
-			err = -EAGAIN;
-			/* SKB consumed by dev_direct_xmit() */
+			/* SKB completed but not sent */
+			err = -EBUSY;
 			goto out;
 		}
 
 		sent_frame = true;
-		xskq_discard_desc(xs->tx);
 	}
 
 out:
@@ -755,6 +758,7 @@ static int xsk_create(struct net *net, struct socket *sock, int protocol,
 
 	xs = xdp_sk(sk);
 	mutex_init(&xs->mutex);
+	spin_lock_init(&xs->tx_completion_lock);
 
 	local_bh_disable();
 	sock_prot_inuse_add(net, &xsk_proto, 1);
diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
index ef6a6f0ec949..52ecaf770642 100644
--- a/net/xdp/xsk_queue.h
+++ b/net/xdp/xsk_queue.h
@@ -62,14 +62,9 @@ static inline u32 xskq_nb_avail(struct xsk_queue *q, u32 dcnt)
 	return (entries > dcnt) ? dcnt : entries;
 }
 
-static inline u32 xskq_nb_free_lazy(struct xsk_queue *q, u32 producer)
-{
-	return q->nentries - (producer - q->cons_tail);
-}
-
 static inline u32 xskq_nb_free(struct xsk_queue *q, u32 producer, u32 dcnt)
 {
-	u32 free_entries = xskq_nb_free_lazy(q, producer);
+	u32 free_entries = q->nentries - (producer - q->cons_tail);
 
 	if (free_entries >= dcnt)
 		return free_entries;
@@ -129,7 +124,7 @@ static inline int xskq_produce_addr(struct xsk_queue *q, u64 addr)
 {
 	struct xdp_umem_ring *ring = (struct xdp_umem_ring *)q->ring;
 
-	if (xskq_nb_free(q, q->prod_tail, LAZY_UPDATE_THRESHOLD) == 0)
+	if (xskq_nb_free(q, q->prod_tail, 1) == 0)
 		return -ENOSPC;
 
 	ring->desc[q->prod_tail++ & q->ring_mask] = addr;
diff --git a/samples/bpf/xdpsock_user.c b/samples/bpf/xdpsock_user.c
index d69c8d78d3fd..5904b1543831 100644
--- a/samples/bpf/xdpsock_user.c
+++ b/samples/bpf/xdpsock_user.c
@@ -729,7 +729,7 @@ static void kick_tx(int fd)
 	int ret;
 
 	ret = sendto(fd, NULL, 0, MSG_DONTWAIT, NULL, 0);
-	if (ret >= 0 || errno == ENOBUFS || errno == EAGAIN)
+	if (ret >= 0 || errno == ENOBUFS || errno == EAGAIN || errno == EBUSY)
 		return;
 	lassert(0);
 }