diff mbox series

[4.19,07/38] vsock/virtio: stop workers during the .remove()

Message ID 20201005142109.015282314@linuxfoundation.org
State New
Headers show
Series None | expand

Commit Message

Greg KH Oct. 5, 2020, 3:26 p.m. UTC 
From: Stefano Garzarella <sgarzare@redhat.com>

[ Upstream commit 17dd1367389cfe7f150790c83247b68e0c19d106 ]

Before to call vdev->config->reset(vdev) we need to be sure that
no one is accessing the device, for this reason, we add new variables
in the struct virtio_vsock to stop the workers during the .remove().

This patch also add few comments before vdev->config->reset(vdev)
and vdev->config->del_vqs(vdev).

Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/vmw_vsock/virtio_transport.c | 51 +++++++++++++++++++++++++++++++-
 1 file changed, 50 insertions(+), 1 deletion(-)

Comments

Pavel Machek Oct. 6, 2020, 7:34 p.m. UTC | #1 
Hi!

> [ Upstream commit 17dd1367389cfe7f150790c83247b68e0c19d106 ]
> 
> Before to call vdev->config->reset(vdev) we need to be sure that
> no one is accessing the device, for this reason, we add new variables
> in the struct virtio_vsock to stop the workers during the .remove().
> 
> This patch also add few comments before vdev->config->reset(vdev)
> and vdev->config->del_vqs(vdev).


> @@ -621,12 +645,18 @@ static int virtio_vsock_probe(struct virtio_device *vdev)
>  	INIT_WORK(&vsock->send_pkt_work, virtio_transport_send_pkt_work);
>  	INIT_WORK(&vsock->loopback_work, virtio_transport_loopback_work);
>  
> +	mutex_lock(&vsock->tx_lock);
> +	vsock->tx_run = true;
> +	mutex_unlock(&vsock->tx_lock);
> +
>  	mutex_lock(&vsock->rx_lock);
>  	virtio_vsock_rx_fill(vsock);
> +	vsock->rx_run = true;
>  	mutex_unlock(&vsock->rx_lock);
>  
>  	mutex_lock(&vsock->event_lock);
>  	virtio_vsock_event_fill(vsock);
> +	vsock->event_run = true;
>  	mutex_unlock(&vsock->event_lock);
>

This looks like some kind of voodoo code. Locks are just being
allocated few lines above, so there are no other threads accessing
*vsock. That means we don't need to take the locks... right?

At least taking the tx_lock is unneccessary, but probably the others,
too...

Best regards,
									Pavel
Stefano Garzarella Oct. 7, 2020, 7:13 a.m. UTC | #2 
On Tue, Oct 06, 2020 at 09:34:32PM +0200, Pavel Machek wrote:
> Hi!

> 

> > [ Upstream commit 17dd1367389cfe7f150790c83247b68e0c19d106 ]

> > 

> > Before to call vdev->config->reset(vdev) we need to be sure that

> > no one is accessing the device, for this reason, we add new variables

> > in the struct virtio_vsock to stop the workers during the .remove().

> > 

> > This patch also add few comments before vdev->config->reset(vdev)

> > and vdev->config->del_vqs(vdev).

> 

> 

> > @@ -621,12 +645,18 @@ static int virtio_vsock_probe(struct virtio_device *vdev)

> >  	INIT_WORK(&vsock->send_pkt_work, virtio_transport_send_pkt_work);

> >  	INIT_WORK(&vsock->loopback_work, virtio_transport_loopback_work);

> >  

> > +	mutex_lock(&vsock->tx_lock);

> > +	vsock->tx_run = true;

> > +	mutex_unlock(&vsock->tx_lock);

> > +

> >  	mutex_lock(&vsock->rx_lock);

> >  	virtio_vsock_rx_fill(vsock);

> > +	vsock->rx_run = true;

> >  	mutex_unlock(&vsock->rx_lock);

> >  

> >  	mutex_lock(&vsock->event_lock);

> >  	virtio_vsock_event_fill(vsock);

> > +	vsock->event_run = true;

> >  	mutex_unlock(&vsock->event_lock);

> >

> 

> This looks like some kind of voodoo code. Locks are just being

> allocated few lines above, so there are no other threads accessing

> *vsock. That means we don't need to take the locks... right?

> 

> At least taking the tx_lock is unneccessary, but probably the others,

> too...


Before commit 0deab087b16a ("vsock/virtio: use RCU to avoid use-after-free
on the_virtio_vsock") we assigned 'the_virtio_vsock pointer' before this
section, so this should be the reason of these locks.

Now that we moved the assignment at the end of the probe(), we can clean
a bit, especially the tx_lock.

I'll take a look.

Thanks,
Stefano
diff mbox series

Patch

diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index 68186419c445f..4bc217ef56945 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -39,6 +39,7 @@  struct virtio_vsock {
 	 * must be accessed with tx_lock held.
 	 */
 	struct mutex tx_lock;
+	bool tx_run;
 
 	struct work_struct send_pkt_work;
 	spinlock_t send_pkt_list_lock;
@@ -54,6 +55,7 @@  struct virtio_vsock {
 	 * must be accessed with rx_lock held.
 	 */
 	struct mutex rx_lock;
+	bool rx_run;
 	int rx_buf_nr;
 	int rx_buf_max_nr;
 
@@ -61,6 +63,7 @@  struct virtio_vsock {
 	 * vqs[VSOCK_VQ_EVENT] must be accessed with event_lock held.
 	 */
 	struct mutex event_lock;
+	bool event_run;
 	struct virtio_vsock_event event_list[8];
 
 	u32 guest_cid;
@@ -95,6 +98,10 @@  static void virtio_transport_loopback_work(struct work_struct *work)
 	spin_unlock_bh(&vsock->loopback_list_lock);
 
 	mutex_lock(&vsock->rx_lock);
+
+	if (!vsock->rx_run)
+		goto out;
+
 	while (!list_empty(&pkts)) {
 		struct virtio_vsock_pkt *pkt;
 
@@ -103,6 +110,7 @@  static void virtio_transport_loopback_work(struct work_struct *work)
 
 		virtio_transport_recv_pkt(pkt);
 	}
+out:
 	mutex_unlock(&vsock->rx_lock);
 }
 
@@ -131,6 +139,9 @@  virtio_transport_send_pkt_work(struct work_struct *work)
 
 	mutex_lock(&vsock->tx_lock);
 
+	if (!vsock->tx_run)
+		goto out;
+
 	vq = vsock->vqs[VSOCK_VQ_TX];
 
 	for (;;) {
@@ -189,6 +200,7 @@  virtio_transport_send_pkt_work(struct work_struct *work)
 	if (added)
 		virtqueue_kick(vq);
 
+out:
 	mutex_unlock(&vsock->tx_lock);
 
 	if (restart_rx)
@@ -324,6 +336,10 @@  static void virtio_transport_tx_work(struct work_struct *work)
 
 	vq = vsock->vqs[VSOCK_VQ_TX];
 	mutex_lock(&vsock->tx_lock);
+
+	if (!vsock->tx_run)
+		goto out;
+
 	do {
 		struct virtio_vsock_pkt *pkt;
 		unsigned int len;
@@ -334,6 +350,8 @@  static void virtio_transport_tx_work(struct work_struct *work)
 			added = true;
 		}
 	} while (!virtqueue_enable_cb(vq));
+
+out:
 	mutex_unlock(&vsock->tx_lock);
 
 	if (added)
@@ -362,6 +380,9 @@  static void virtio_transport_rx_work(struct work_struct *work)
 
 	mutex_lock(&vsock->rx_lock);
 
+	if (!vsock->rx_run)
+		goto out;
+
 	do {
 		virtqueue_disable_cb(vq);
 		for (;;) {
@@ -471,6 +492,9 @@  static void virtio_transport_event_work(struct work_struct *work)
 
 	mutex_lock(&vsock->event_lock);
 
+	if (!vsock->event_run)
+		goto out;
+
 	do {
 		struct virtio_vsock_event *event;
 		unsigned int len;
@@ -485,7 +509,7 @@  static void virtio_transport_event_work(struct work_struct *work)
 	} while (!virtqueue_enable_cb(vq));
 
 	virtqueue_kick(vsock->vqs[VSOCK_VQ_EVENT]);
-
+out:
 	mutex_unlock(&vsock->event_lock);
 }
 
@@ -621,12 +645,18 @@  static int virtio_vsock_probe(struct virtio_device *vdev)
 	INIT_WORK(&vsock->send_pkt_work, virtio_transport_send_pkt_work);
 	INIT_WORK(&vsock->loopback_work, virtio_transport_loopback_work);
 
+	mutex_lock(&vsock->tx_lock);
+	vsock->tx_run = true;
+	mutex_unlock(&vsock->tx_lock);
+
 	mutex_lock(&vsock->rx_lock);
 	virtio_vsock_rx_fill(vsock);
+	vsock->rx_run = true;
 	mutex_unlock(&vsock->rx_lock);
 
 	mutex_lock(&vsock->event_lock);
 	virtio_vsock_event_fill(vsock);
+	vsock->event_run = true;
 	mutex_unlock(&vsock->event_lock);
 
 	vdev->priv = vsock;
@@ -661,6 +691,24 @@  static void virtio_vsock_remove(struct virtio_device *vdev)
 	/* Reset all connected sockets when the device disappear */
 	vsock_for_each_connected_socket(virtio_vsock_reset_sock);
 
+	/* Stop all work handlers to make sure no one is accessing the device,
+	 * so we can safely call vdev->config->reset().
+	 */
+	mutex_lock(&vsock->rx_lock);
+	vsock->rx_run = false;
+	mutex_unlock(&vsock->rx_lock);
+
+	mutex_lock(&vsock->tx_lock);
+	vsock->tx_run = false;
+	mutex_unlock(&vsock->tx_lock);
+
+	mutex_lock(&vsock->event_lock);
+	vsock->event_run = false;
+	mutex_unlock(&vsock->event_lock);
+
+	/* Flush all device writes and interrupts, device will not use any
+	 * more buffers.
+	 */
 	vdev->config->reset(vdev);
 
 	mutex_lock(&vsock->rx_lock);
@@ -691,6 +739,7 @@  static void virtio_vsock_remove(struct virtio_device *vdev)
 	}
 	spin_unlock_bh(&vsock->loopback_list_lock);
 
+	/* Delete virtqueues and flush outstanding callbacks if any */
 	vdev->config->del_vqs(vdev);
 
 	mutex_unlock(&the_virtio_vsock_mutex);