Subject: Re: [PATCH v3 2/4] VSOCK: Introduce virtio-vsock.ko

From: Alex Bennée <[email-masked]>
Date: Thu, 10 Dec 2015 21:23:25 +0000

Stefan Hajnoczi <[email-masked]> writes:

> From: Asias He <[email-masked]>
>
> VM sockets virtio transport implementation. This module runs in guest
> kernel.

checkpatch warns on a bunch of whitespace/tab issues.

>
> Signed-off-by: Asias He <[email-masked]>
> Signed-off-by: Stefan Hajnoczi <[email-masked]>
> ---
> v2:
>  * Fix total_tx_buf accounting
>  * Add virtio_transport global mutex to prevent races
> ---
>  net/vmw_vsock/virtio_transport.c | 466 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 466 insertions(+)
>  create mode 100644 net/vmw_vsock/virtio_transport.c
>
> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> new file mode 100644
> index 0000000..df65dca
> --- /dev/null
> +++ b/net/vmw_vsock/virtio_transport.c
> @@ -0,0 +1,466 @@
> +/*
> + * virtio transport for vsock
> + *
> + * Copyright (C) 2013-2015 Red Hat, Inc.
> + * Author: Asias He <[email-masked]>
> + *         Stefan Hajnoczi <[email-masked]>
> + *
> + * Some of the code is take from Gerd Hoffmann <[email-masked]>'s
> + * early virtio-vsock proof-of-concept bits.
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2.
> + */
> +#include <linux/spinlock.h>
> +#include <linux/module.h>
> +#include <linux/list.h>
> +#include <linux/virtio.h>
> +#include <linux/virtio_ids.h>
> +#include <linux/virtio_config.h>
> +#include <linux/virtio_vsock.h>
> +#include <net/sock.h>
> +#include <linux/mutex.h>
> +#include <net/af_vsock.h>
> +
> +static struct workqueue_struct *virtio_vsock_workqueue;
> +static struct virtio_vsock *the_virtio_vsock;
> +static DEFINE_MUTEX(the_virtio_vsock_mutex); /* protects the_virtio_vsock */
> +static void virtio_vsock_rx_fill(struct virtio_vsock *vsock);
> +
> +struct virtio_vsock {
> +	/* Virtio device */
> +	struct virtio_device *vdev;
> +	/* Virtio virtqueue */
> +	struct virtqueue *vqs[VSOCK_VQ_MAX];
> +	/* Wait queue for send pkt */
> +	wait_queue_head_t queue_wait;
> +	/* Work item to send pkt */
> +	struct work_struct tx_work;
> +	/* Work item to recv pkt */
> +	struct work_struct rx_work;
> +	/* Mutex to protect send pkt*/
> +	struct mutex tx_lock;
> +	/* Mutex to protect recv pkt*/
> +	struct mutex rx_lock;

Further down I got confused by what lock was what and exactly what was
being protected. If the receive and transmit paths touch separate things
it might be worth re-arranging the structure to make it clearer, eg:

   /* The transmit path is protected by tx_lock */
   struct mutex tx_lock;
   struct work_struct tx_work;
   ..
   ..

   /* The receive path is protected by rx_lock */
   wait_queue_head_t queue_wait;
   ..
   ..

 Which might make things a little clearer. Then all the redundant
 information in the comments can be removed. I don't need to know what
 is a Virtio device, virtqueue or wait_queue etc as they are implicit in
 the structure name.

> +	/* Number of recv buffers */
> +	int rx_buf_nr;
> +	/* Number of max recv buffers */
> +	int rx_buf_max_nr;
> +	/* Used for global tx buf limitation */
> +	u32 total_tx_buf;
> +	/* Guest context id, just like guest ip address */
> +	u32 guest_cid;
> +};
> +
> +static struct virtio_vsock *virtio_vsock_get(void)
> +{
> +	return the_virtio_vsock;
> +}
> +
> +static u32 virtio_transport_get_local_cid(void)
> +{
> +	struct virtio_vsock *vsock = virtio_vsock_get();
> +
> +	return vsock->guest_cid;
> +}
> +
> +static int
> +virtio_transport_send_pkt(struct vsock_sock *vsk,
> +			  struct virtio_vsock_pkt_info *info)
> +{
> +	u32 src_cid, src_port, dst_cid, dst_port;
> +	int ret, in_sg = 0, out_sg = 0;
> +	struct virtio_transport *trans;
> +	struct virtio_vsock_pkt *pkt;
> +	struct virtio_vsock *vsock;
> +	struct scatterlist hdr, buf, *sgs[2];
> +	struct virtqueue *vq;
> +	u32 pkt_len = info->pkt_len;
> +	DEFINE_WAIT(wait);
> +
> +	vsock = virtio_vsock_get();
> +	if (!vsock)
> +		return -ENODEV;
> +
> +	src_cid	= virtio_transport_get_local_cid();
> +	src_port = vsk->local_addr.svm_port;
> +	if (!info->remote_cid) {
> +		dst_cid	= vsk->remote_addr.svm_cid;
> +		dst_port = vsk->remote_addr.svm_port;
> +	} else {
> +		dst_cid = info->remote_cid;
> +		dst_port = info->remote_port;
> +	}
> +
> +	trans = vsk->trans;
> +	vq = vsock->vqs[VSOCK_VQ_TX];
> +
> +	if (pkt_len > VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE)
> +		pkt_len = VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE;
> +	pkt_len = virtio_transport_get_credit(trans, pkt_len);
> +	/* Do not send zero length OP_RW pkt*/
> +	if (pkt_len == 0 && info->op == VIRTIO_VSOCK_OP_RW)
> +		return pkt_len;
> +
> +	/* Respect global tx buf limitation */
> +	mutex_lock(&vsock->tx_lock);
> +	while (pkt_len + vsock->total_tx_buf > VIRTIO_VSOCK_MAX_TX_BUF_SIZE) {
> +		prepare_to_wait_exclusive(&vsock->queue_wait, &wait,
> +					  TASK_UNINTERRUPTIBLE);
> +		mutex_unlock(&vsock->tx_lock);
> +		schedule();
> +		mutex_lock(&vsock->tx_lock);
> +		finish_wait(&vsock->queue_wait, &wait);
> +	}
> +	vsock->total_tx_buf += pkt_len;
> +	mutex_unlock(&vsock->tx_lock);
> +
> +	pkt = virtio_transport_alloc_pkt(vsk, info, pkt_len,
> +					 src_cid, src_port,
> +					 dst_cid, dst_port);
> +	if (!pkt) {
> +		mutex_lock(&vsock->tx_lock);
> +		vsock->total_tx_buf -= pkt_len;
> +		mutex_unlock(&vsock->tx_lock);
> +		virtio_transport_put_credit(trans, pkt_len);
> +		return -ENOMEM;
> +	}
> +
> +	pr_debug("%s:info->pkt_len= %d\n", __func__, info->pkt_len);
> +
> +	/* Will be released in virtio_transport_send_pkt_work */
> +	sock_hold(&trans->vsk->sk);
> +	virtio_transport_inc_tx_pkt(pkt);
> +
> +	/* Put pkt in the virtqueue */
> +	sg_init_one(&hdr, &pkt->hdr, sizeof(pkt->hdr));
> +	sgs[out_sg++] = &hdr;
> +	if (info->msg && info->pkt_len > 0) {
> +		sg_init_one(&buf, pkt->buf, pkt->len);
> +	        sgs[out_sg++] = &buf;
> +	}
> +
> +	mutex_lock(&vsock->tx_lock);
> +	while ((ret = virtqueue_add_sgs(vq, sgs, out_sg, in_sg, pkt,
> +					GFP_KERNEL)) < 0) {
> +		prepare_to_wait_exclusive(&vsock->queue_wait, &wait,
> +					  TASK_UNINTERRUPTIBLE);
> +		mutex_unlock(&vsock->tx_lock);
> +		schedule();
> +		mutex_lock(&vsock->tx_lock);
> +		finish_wait(&vsock->queue_wait, &wait);
> +	}
> +	virtqueue_kick(vq);
> +	mutex_unlock(&vsock->tx_lock);

What are we protecting with tx_lock here? See comments above about
making the lock usage semantics clearer.

> +
> +	return pkt_len;
> +}
> +
> +static struct virtio_transport_pkt_ops virtio_ops = {
> +	.send_pkt = virtio_transport_send_pkt,
> +};
> +
> +static void virtio_vsock_rx_fill(struct virtio_vsock *vsock)
> +{
> +	int buf_len = VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE;
> +	struct virtio_vsock_pkt *pkt;
> +	struct scatterlist hdr, buf, *sgs[2];
> +	struct virtqueue *vq;
> +	int ret;
> +
> +	vq = vsock->vqs[VSOCK_VQ_RX];
> +
> +	do {
> +		pkt = kzalloc(sizeof(*pkt), GFP_KERNEL);
> +		if (!pkt) {
> +			pr_debug("%s: fail to allocate pkt\n", __func__);
> +			goto out;
> +		}
> +
> +		/* TODO: use mergeable rx buffer */

TODO's should end up in merged code.

> +		pkt->buf = kmalloc(buf_len, GFP_KERNEL);
> +		if (!pkt->buf) {
> +			pr_debug("%s: fail to allocate pkt->buf\n", __func__);
> +			goto err;
> +		}
> +
> +		sg_init_one(&hdr, &pkt->hdr, sizeof(pkt->hdr));
> +		sgs[0] = &hdr;
> +
> +		sg_init_one(&buf, pkt->buf, buf_len);
> +	        sgs[1] = &buf;
> +		ret = virtqueue_add_sgs(vq, sgs, 0, 2, pkt, GFP_KERNEL);
> +		if (ret)
> +			goto err;
> +		vsock->rx_buf_nr++;
> +	} while (vq->num_free);
> +	if (vsock->rx_buf_nr > vsock->rx_buf_max_nr)
> +		vsock->rx_buf_max_nr = vsock->rx_buf_nr;
> +out:
> +	virtqueue_kick(vq);
> +	return;
> +err:
> +	virtqueue_kick(vq);
> +	virtio_transport_free_pkt(pkt);

You could free the pkt memory at the fail site and just have one exit path.

> +	return;
> +}
> +
> +static void virtio_transport_send_pkt_work(struct work_struct *work)
> +{
> +	struct virtio_vsock *vsock =
> +		container_of(work, struct virtio_vsock, tx_work);
> +	struct virtio_vsock_pkt *pkt;
> +	bool added = false;
> +	struct virtqueue *vq;
> +	unsigned int len;
> +	struct sock *sk;
> +
> +	vq = vsock->vqs[VSOCK_VQ_TX];
> +	mutex_lock(&vsock->tx_lock);
> +	do {

You can move the declarations of pkt/len into the do block.

> +		virtqueue_disable_cb(vq);
> +		while ((pkt = virtqueue_get_buf(vq, &len)) != NULL) {

And the sk declaration here

> +			sk = &pkt->trans->vsk->sk;
> +			virtio_transport_dec_tx_pkt(pkt);
> +			/* Release refcnt taken in virtio_transport_send_pkt */
> +			sock_put(sk);
> +			vsock->total_tx_buf -= pkt->len;
> +			virtio_transport_free_pkt(pkt);
> +			added = true;
> +		}
> +	} while (!virtqueue_enable_cb(vq));
> +	mutex_unlock(&vsock->tx_lock);
> +
> +	if (added)
> +		wake_up(&vsock->queue_wait);
> +}
> +
> +static void virtio_transport_recv_pkt_work(struct work_struct *work)
> +{
> +	struct virtio_vsock *vsock =
> +		container_of(work, struct virtio_vsock, rx_work);
> +	struct virtio_vsock_pkt *pkt;
> +	struct virtqueue *vq;
> +	unsigned int len;

Same as above for pkt, len.

> +
> +	vq = vsock->vqs[VSOCK_VQ_RX];
> +	mutex_lock(&vsock->rx_lock);
> +	do {
> +		virtqueue_disable_cb(vq);
> +		while ((pkt = virtqueue_get_buf(vq, &len)) != NULL) {
> +			pkt->len = len;
> +			virtio_transport_recv_pkt(pkt);
> +			vsock->rx_buf_nr--;
> +		}
> +	} while (!virtqueue_enable_cb(vq));
> +
> +	if (vsock->rx_buf_nr < vsock->rx_buf_max_nr / 2)
> +		virtio_vsock_rx_fill(vsock);
> +	mutex_unlock(&vsock->rx_lock);
> +}
> +
> +static void virtio_vsock_ctrl_done(struct virtqueue *vq)
> +{
> +}
> +
> +static void virtio_vsock_tx_done(struct virtqueue *vq)
> +{
> +	struct virtio_vsock *vsock = vq->vdev->priv;
> +
> +	if (!vsock)
> +		return;
> +	queue_work(virtio_vsock_workqueue, &vsock->tx_work);
> +}
> +
> +static void virtio_vsock_rx_done(struct virtqueue *vq)
> +{
> +	struct virtio_vsock *vsock = vq->vdev->priv;
> +
> +	if (!vsock)
> +		return;
> +	queue_work(virtio_vsock_workqueue, &vsock->rx_work);
> +}
> +
> +static int
> +virtio_transport_socket_init(struct vsock_sock *vsk, struct vsock_sock *psk)
> +{
> +	struct virtio_transport *trans;
> +	int ret;
> +
> +	ret = virtio_transport_do_socket_init(vsk, psk);
> +	if (ret)
> +		return ret;
> +
> +	trans = vsk->trans;
> +	trans->ops = &virtio_ops;
> +	return ret;
> +}
> +
> +static struct vsock_transport virtio_transport = {
> +	.get_local_cid            = virtio_transport_get_local_cid,
> +
> +	.init                     = virtio_transport_socket_init,
> +	.destruct                 = virtio_transport_destruct,
> +	.release                  = virtio_transport_release,
> +	.connect                  = virtio_transport_connect,
> +	.shutdown                 = virtio_transport_shutdown,
> +
> +	.dgram_bind               = virtio_transport_dgram_bind,
> +	.dgram_dequeue            = virtio_transport_dgram_dequeue,
> +	.dgram_enqueue            = virtio_transport_dgram_enqueue,
> +	.dgram_allow              = virtio_transport_dgram_allow,
> +
> +	.stream_dequeue           = virtio_transport_stream_dequeue,
> +	.stream_enqueue           = virtio_transport_stream_enqueue,
> +	.stream_has_data          = virtio_transport_stream_has_data,
> +	.stream_has_space         = virtio_transport_stream_has_space,
> +	.stream_rcvhiwat          = virtio_transport_stream_rcvhiwat,
> +	.stream_is_active         = virtio_transport_stream_is_active,
> +	.stream_allow             = virtio_transport_stream_allow,
> +
> +	.notify_poll_in           = virtio_transport_notify_poll_in,
> +	.notify_poll_out          = virtio_transport_notify_poll_out,
> +	.notify_recv_init         = virtio_transport_notify_recv_init,
> +	.notify_recv_pre_block    = virtio_transport_notify_recv_pre_block,
> +	.notify_recv_pre_dequeue  = virtio_transport_notify_recv_pre_dequeue,
> +	.notify_recv_post_dequeue = virtio_transport_notify_recv_post_dequeue,
> +	.notify_send_init         = virtio_transport_notify_send_init,
> +	.notify_send_pre_block    = virtio_transport_notify_send_pre_block,
> +	.notify_send_pre_enqueue  = virtio_transport_notify_send_pre_enqueue,
> +	.notify_send_post_enqueue = virtio_transport_notify_send_post_enqueue,
> +
> +	.set_buffer_size          = virtio_transport_set_buffer_size,
> +	.set_min_buffer_size      = virtio_transport_set_min_buffer_size,
> +	.set_max_buffer_size      = virtio_transport_set_max_buffer_size,
> +	.get_buffer_size          = virtio_transport_get_buffer_size,
> +	.get_min_buffer_size      = virtio_transport_get_min_buffer_size,
> +	.get_max_buffer_size      = virtio_transport_get_max_buffer_size,
> +};
> +
> +static int virtio_vsock_probe(struct virtio_device *vdev)
> +{
> +	vq_callback_t *callbacks[] = {
> +		virtio_vsock_ctrl_done,
> +		virtio_vsock_rx_done,
> +		virtio_vsock_tx_done,
> +	};
> +	const char *names[] = {
> +		"ctrl",
> +		"rx",
> +		"tx",
> +	};
> +	struct virtio_vsock *vsock = NULL;
> +	u32 guest_cid;
> +	int ret;
> +
> +	ret = mutex_lock_interruptible(&the_virtio_vsock_mutex);
> +	if (ret)
> +		return ret;
> +
> +	/* Only one virtio-vsock device per guest is supported */
> +	if (the_virtio_vsock) {
> +		ret = -EBUSY;
> +		goto out;
> +	}
> +
> +	vsock = kzalloc(sizeof(*vsock), GFP_KERNEL);
> +	if (!vsock) {
> +		ret = -ENOMEM;
> +		goto out;

Won't this attempt to kfree a NULL vsock?

> +	}
> +
> +	vsock->vdev = vdev;
> +
> +	ret = vsock->vdev->config->find_vqs(vsock->vdev, VSOCK_VQ_MAX,
> +					    vsock->vqs, callbacks, names);
> +	if (ret < 0)
> +		goto out;
> +
> +	vdev->config->get(vdev, offsetof(struct virtio_vsock_config, guest_cid),
> +			  &guest_cid, sizeof(guest_cid));
> +	vsock->guest_cid = le32_to_cpu(guest_cid);
> +	pr_debug("%s:guest_cid=%d\n", __func__, vsock->guest_cid);
> +
> +	ret = vsock_core_init(&virtio_transport);
> +	if (ret < 0)
> +		goto out_vqs;
> +
> +	vsock->rx_buf_nr = 0;
> +	vsock->rx_buf_max_nr = 0;
> +
> +	vdev->priv = the_virtio_vsock = vsock;
> +	init_waitqueue_head(&vsock->queue_wait);
> +	mutex_init(&vsock->tx_lock);
> +	mutex_init(&vsock->rx_lock);
> +	INIT_WORK(&vsock->rx_work, virtio_transport_recv_pkt_work);
> +	INIT_WORK(&vsock->tx_work, virtio_transport_send_pkt_work);
> +
> +	mutex_lock(&vsock->rx_lock);
> +	virtio_vsock_rx_fill(vsock);
> +	mutex_unlock(&vsock->rx_lock);
> +
> +	mutex_unlock(&the_virtio_vsock_mutex);
> +	return 0;
> +
> +out_vqs:
> +	vsock->vdev->config->del_vqs(vsock->vdev);
> +out:
> +	kfree(vsock);
> +	mutex_unlock(&the_virtio_vsock_mutex);
> +	return ret;
> +}
> +
> +static void virtio_vsock_remove(struct virtio_device *vdev)
> +{
> +	struct virtio_vsock *vsock = vdev->priv;
> +
> +	mutex_lock(&the_virtio_vsock_mutex);
> +	the_virtio_vsock = NULL;
> +	vsock_core_exit();
> +	mutex_unlock(&the_virtio_vsock_mutex);
> +
> +	kfree(vsock);
> +}
> +
> +static struct virtio_device_id id_table[] = {
> +	{ VIRTIO_ID_VSOCK, VIRTIO_DEV_ANY_ID },
> +	{ 0 },
> +};
> +
> +static unsigned int features[] = {
> +};
> +
> +static struct virtio_driver virtio_vsock_driver = {
> +	.feature_table = features,
> +	.feature_table_size = ARRAY_SIZE(features),
> +	.driver.name = KBUILD_MODNAME,
> +	.driver.owner = THIS_MODULE,
> +	.id_table = id_table,
> +	.probe = virtio_vsock_probe,
> +	.remove = virtio_vsock_remove,
> +};
> +
> +static int __init virtio_vsock_init(void)
> +{
> +	int ret;
> +
> +	virtio_vsock_workqueue = alloc_workqueue("virtio_vsock", 0, 0);
> +	if (!virtio_vsock_workqueue)
> +		return -ENOMEM;
> +	ret = register_virtio_driver(&virtio_vsock_driver);
> +	if (ret)
> +		destroy_workqueue(virtio_vsock_workqueue);
> +	return ret;
> +}
> +
> +static void __exit virtio_vsock_exit(void)
> +{
> +	unregister_virtio_driver(&virtio_vsock_driver);
> +	destroy_workqueue(virtio_vsock_workqueue);
> +}
> +
> +module_init(virtio_vsock_init);
> +module_exit(virtio_vsock_exit);
> +MODULE_LICENSE("GPL v2");
> +MODULE_AUTHOR("Asias He");
> +MODULE_DESCRIPTION("virtio transport for vsock");
> +MODULE_DEVICE_TABLE(virtio, id_table);

--
Alex Bennée
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