[PATCH V2 0/3] handle polling errors in vhost/vhost_net

@@ -64,20 +64,10 @@ enum {
 	VHOST_NET_VQ_MAX = 2,
 };
 
-enum vhost_net_poll_state {
-	VHOST_NET_POLL_DISABLED = 0,
-	VHOST_NET_POLL_STARTED = 1,
-	VHOST_NET_POLL_STOPPED = 2,
-};
-
 struct vhost_net {
 	struct vhost_dev dev;
 	struct vhost_virtqueue vqs[VHOST_NET_VQ_MAX];
 	struct vhost_poll poll[VHOST_NET_VQ_MAX];
-	/* Tells us whether we are polling a socket for TX.
-	 * We only do this when socket buffer fills up.
-	 * Protected by tx vq lock. */
-	enum vhost_net_poll_state tx_poll_state;
 	/* Number of TX recently submitted.
 	 * Protected by tx vq lock. */
 	unsigned tx_packets;

@@ -155,24 +145,6 @@ static void copy_iovec_hdr(const struct iovec *from, struct iovec *to,
 	}
 }
 
-/* Caller must have TX VQ lock */
-static void tx_poll_stop(struct vhost_net *net)
-{
-	if (likely(net->tx_poll_state != VHOST_NET_POLL_STARTED))
-		return;
-	vhost_poll_stop(net->poll + VHOST_NET_VQ_TX);
-	net->tx_poll_state = VHOST_NET_POLL_STOPPED;
-}
-
-/* Caller must have TX VQ lock */
-static void tx_poll_start(struct vhost_net *net, struct socket *sock)
-{
-	if (unlikely(net->tx_poll_state != VHOST_NET_POLL_STOPPED))
-		return;
-	vhost_poll_start(net->poll + VHOST_NET_VQ_TX, sock->file);
-	net->tx_poll_state = VHOST_NET_POLL_STARTED;
-}
-
 /* In case of DMA done not in order in lower device driver for some reason.
  * upend_idx is used to track end of used idx, done_idx is used to track head
  * of used idx. Once lower device DMA done contiguously, we will signal KVM

@@ -227,6 +199,7 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success)
 static void handle_tx(struct vhost_net *net)
 {
 	struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_TX];
+	struct vhost_poll *poll = net->poll + VHOST_NET_VQ_TX;
 	unsigned out, in, s;
 	int head;
 	struct msghdr msg = {

@@ -252,7 +225,8 @@ static void handle_tx(struct vhost_net *net)
 	wmem = atomic_read(&sock->sk->sk_wmem_alloc);
 	if (wmem >= sock->sk->sk_sndbuf) {
 		mutex_lock(&vq->mutex);
-		tx_poll_start(net, sock);
+		if (vhost_poll_start(poll, sock->file))
+			vq_err(vq, "Fail to poll TX\n");
 		mutex_unlock(&vq->mutex);
 		return;
 	}

@@ -261,7 +235,7 @@ static void handle_tx(struct vhost_net *net)
 	vhost_disable_notify(&net->dev, vq);
 
 	if (wmem < sock->sk->sk_sndbuf / 2)
-		tx_poll_stop(net);
+		vhost_poll_stop(poll);
 	hdr_size = vq->vhost_hlen;
 	zcopy = vq->ubufs;
 

@@ -283,7 +257,10 @@ static void handle_tx(struct vhost_net *net)
 
 			wmem = atomic_read(&sock->sk->sk_wmem_alloc);
 			if (wmem >= sock->sk->sk_sndbuf * 3 / 4) {
-				tx_poll_start(net, sock);
+				if (vhost_poll_start(poll, sock->file)) {
+					vq_err(vq, "Fail to poll TX\n");
+					break;
+				}
 				set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
 				break;
 			}

@@ -294,7 +271,10 @@ static void handle_tx(struct vhost_net *net)
 				    (vq->upend_idx - vq->done_idx) :
 				    (vq->upend_idx + UIO_MAXIOV - vq->done_idx);
 			if (unlikely(num_pends > VHOST_MAX_PEND)) {
-				tx_poll_start(net, sock);
+				if (vhost_poll_start(poll, sock->file)) {
+					vq_err(vq, "Fail to poll TX\n");
+					break;
+				}
 				set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
 				break;
 			}

@@ -360,7 +340,8 @@ static void handle_tx(struct vhost_net *net)
 			}
 			vhost_discard_vq_desc(vq, 1);
 			if (err == -EAGAIN || err == -ENOBUFS)
-				tx_poll_start(net, sock);
+				if (vhost_poll_start(poll, sock->file))
+					vq_err(vq, "fail to poll TX\n");
 			break;
 		}
 		if (err != len)

@@ -623,7 +604,6 @@ static int vhost_net_open(struct inode *inode, struct file *f)
 
 	vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT, dev);
 	vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN, dev);
-	n->tx_poll_state = VHOST_NET_POLL_DISABLED;
 
 	f->private_data = n;
 

@@ -633,29 +613,26 @@ static int vhost_net_open(struct inode *inode, struct file *f)
 static void vhost_net_disable_vq(struct vhost_net *n,
 				 struct vhost_virtqueue *vq)
 {
+	int index = vq - n->vqs;
 	if (!vq->private_data)
 		return;
-	if (vq == n->vqs + VHOST_NET_VQ_TX) {
-		tx_poll_stop(n);
-		n->tx_poll_state = VHOST_NET_POLL_DISABLED;
-	} else
-		vhost_poll_stop(n->poll + VHOST_NET_VQ_RX);
+	vhost_poll_stop(n->poll + index);
 }
 
-static void vhost_net_enable_vq(struct vhost_net *n,
-				struct vhost_virtqueue *vq)
+static int vhost_net_enable_vq(struct vhost_net *n,
+			       struct vhost_virtqueue *vq)
 {
+	int err, index = vq - n->vqs;
 	struct socket *sock;
 
 	sock = rcu_dereference_protected(vq->private_data,
 					 lockdep_is_held(&vq->mutex));
 	if (!sock)
-		return;
-	if (vq == n->vqs + VHOST_NET_VQ_TX) {
-		n->tx_poll_state = VHOST_NET_POLL_STOPPED;
-		tx_poll_start(n, sock);
-	} else
-		vhost_poll_start(n->poll + VHOST_NET_VQ_RX, sock->file);
+		return 0;
+
+	n->poll[index].state = VHOST_POLL_STOPPED;
+	err = vhost_poll_start(n->poll + index, sock->file);
+	return err;
 }
 
 static struct socket *vhost_net_stop_vq(struct vhost_net *n,

@@ -833,7 +810,9 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
 		r = vhost_init_used(vq);
 		if (r)
 			goto err_used;
-		vhost_net_enable_vq(n, vq);
+		r = vhost_net_enable_vq(n, vq);
+		if (r)
+			goto err_used;
 
 		oldubufs = vq->ubufs;
 		vq->ubufs = ubufs;

@@ -77,26 +77,39 @@ void vhost_poll_init(struct vhost_poll *poll, vhost_work_fn_t fn,
 	init_poll_funcptr(&poll->table, vhost_poll_func);
 	poll->mask = mask;
 	poll->dev = dev;
+	poll->state = VHOST_POLL_DISABLED;
 
 	vhost_work_init(&poll->work, fn);
 }
 
-/* Start polling a file. We add ourselves to file's wait queue. The caller must
- * keep a reference to a file until after vhost_poll_stop is called. */
-void vhost_poll_start(struct vhost_poll *poll, struct file *file)
+/* Start polling a file. We try to add ourselves to file's wait queue. The
+ * caller must keep a reference to a file until after vhost_poll_stop is
+ * called. The file must guarantee that ourselves were not added to the
+ * waitqueue when POLLERR were returned by poll(), vhost_poll_stop() depends on
+ * this behavior. */
+int vhost_poll_start(struct vhost_poll *poll, struct file *file)
 {
 	unsigned long mask;
+	if (unlikely(poll->state != VHOST_POLL_STOPPED))
+		return 0;
 
 	mask = file->f_op->poll(file, &poll->table);
+	if (mask & POLLERR)
+		return -EINVAL;
 	if (mask)
 		vhost_poll_wakeup(&poll->wait, 0, 0, (void *)mask);
+	poll->state = VHOST_POLL_STARTED;
+	return 0;
 }
 
 /* Stop polling a file. After this function returns, it becomes safe to drop the
  * file reference. You must also flush afterwards. */
 void vhost_poll_stop(struct vhost_poll *poll)
 {
+	if (likely(poll->state != VHOST_POLL_STARTED))
+		return;
 	remove_wait_queue(poll->wqh, &poll->wait);
+	poll->state = VHOST_POLL_STOPPED;
 }
 
 static bool vhost_work_seq_done(struct vhost_dev *dev, struct vhost_work *work,

@@ -791,8 +804,10 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp)
 	if (filep)
 		fput(filep);
 
-	if (pollstart && vq->handle_kick)
-		vhost_poll_start(&vq->poll, vq->kick);
+	if (pollstart && vq->handle_kick) {
+		vq->poll.state = VHOST_POLL_STOPPED;
+		r = vhost_poll_start(&vq->poll, vq->kick);
+	}
 
 	mutex_unlock(&vq->mutex);
 

@@ -26,6 +26,12 @@ struct vhost_work {
 	unsigned		  done_seq;
 };
 
+enum vhost_poll_state {
+	VHOST_POLL_DISABLED = 0,
+	VHOST_POLL_STARTED = 1,
+	VHOST_POLL_STOPPED = 2,
+};
+
 /* Poll a file (eventfd or socket) */
 /* Note: there's nothing vhost specific about this structure. */
 struct vhost_poll {

@@ -35,6 +41,9 @@ struct vhost_poll {
 	struct vhost_work	  work;
 	unsigned long		  mask;
 	struct vhost_dev	 *dev;
+	/* Tells us whether we are polling a file.
+	 * Protected by vq lock. */
+	enum vhost_poll_state	  state;
 };
 
 void vhost_work_init(struct vhost_work *work, vhost_work_fn_t fn);

@@ -42,7 +51,7 @@ void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work);
 
 void vhost_poll_init(struct vhost_poll *poll, vhost_work_fn_t fn,
 		     unsigned long mask, struct vhost_dev *dev);
-void vhost_poll_start(struct vhost_poll *poll, struct file *file);
+int vhost_poll_start(struct vhost_poll *poll, struct file *file);
 void vhost_poll_stop(struct vhost_poll *poll);
 void vhost_poll_flush(struct vhost_poll *poll);
 void vhost_poll_queue(struct vhost_poll *poll);

@@ -886,7 +886,7 @@ static unsigned int tun_chr_poll(struct file *file, poll_table *wait)
 	struct sock *sk;
 	unsigned int mask = 0;
 
-	if (!tun)
+	if (!tun || tun->dev->reg_state != NETREG_REGISTERED)
 		return POLLERR;
 
 	sk = tfile->socket.sk;

@@ -903,9 +903,6 @@ static unsigned int tun_chr_poll(struct file *file, poll_table *wait)
 	     sock_writeable(sk)))
 		mask |= POLLOUT | POLLWRNORM;
 
-	if (tun->dev->reg_state != NETREG_REGISTERED)
-		mask = POLLERR;
-
 	tun_put(tun);
 	return mask;
 }

@@ -827,15 +827,16 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
 			r = PTR_ERR(ubufs);
 			goto err_ubufs;
 		}
-		oldubufs = vq->ubufs;
-		vq->ubufs = ubufs;
+
 		vhost_net_disable_vq(n, vq);
 		rcu_assign_pointer(vq->private_data, sock);
-		vhost_net_enable_vq(n, vq);
-
 		r = vhost_init_used(vq);
 		if (r)
-			goto err_vq;
+			goto err_used;
+		vhost_net_enable_vq(n, vq);
+
+		oldubufs = vq->ubufs;
+		vq->ubufs = ubufs;
 
 		n->tx_packets = 0;
 		n->tx_zcopy_err = 0;

@@ -859,6 +860,11 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
 	mutex_unlock(&n->dev.mutex);
 	return 0;
 
+err_used:
+	rcu_assign_pointer(vq->private_data, oldsock);
+	vhost_net_enable_vq(n, vq);
+	if (ubufs)
+		vhost_ubuf_put_and_wait(ubufs);
 err_ubufs:
 	fput(sock->file);
 err_vq: