Linux Virtualization - Aug 2019 - [PATCH v2 2/2] virtio_ring: packed ring: fix virtqueue_detach_unused_buf

This patch series fixes the issue with unplug/replug of a port in virtio
console device, which fails with an error "Error allocating inbufs\n".

Patch 2 makes virtio packed ring code compatible with virtio split ring.
Tested the packed ring code with the qemu virtio 1.1 device code posted
here [1].

Changes from v1[2]
-----
Make virtio packed ring code compatible with split ring - [Michael]

[1]  https://marc.info/?l=qemu-devel&m=156471883703948&w=2
[2] https://lkml.org/lkml/2019/3/4/517

Pankaj Gupta (2):
  virtio_console: free unused buffers with port delete
  virtio_ring: packed ring: fix virtqueue_detach_unused_buf

 drivers/char/virtio_console.c | 14 +++++++++++---
 drivers/virtio/virtio_ring.c  |  5 +++++
 2 files changed, 16 insertions(+), 3 deletions(-)

-- 
2.21.0

The commit a7a69ec0d8e4 ("virtio_console: free buffers after reset")
  deferred detaching of unused buffer to virtio device unplug time.

  This causes unplug/replug of single port in virtio device with an
  error "Error allocating inbufs\n". As we don't free the unused
buffers
  attached with the port. Re-plug the same port tries to allocate new
  buffers in virtqueue and results in this error if queue is full.

  This patch removes the unused buffers in vq's when we unplug the port.
  This is the best we can do as we cannot call device_reset because virtio
  device is still active.

Reported-by: Xiaohui Li <xiaohli at redhat.com>
Fixes: b3258ff1d6 ("virtio_console: free buffers after reset")
Signed-off-by: Pankaj Gupta <pagupta at redhat.com>
---
 drivers/char/virtio_console.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 7270e7b69262..e8be82f1bae9 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -1494,15 +1494,25 @@ static void remove_port(struct kref *kref)
 	kfree(port);
 }
 
+static void remove_unused_bufs(struct virtqueue *vq)
+{
+	struct port_buffer *buf;
+
+	while ((buf = virtqueue_detach_unused_buf(vq)))
+		free_buf(buf, true);
+}
+
 static void remove_port_data(struct port *port)
 {
 	spin_lock_irq(&port->inbuf_lock);
 	/* Remove unused data this port might have received. */
 	discard_port_data(port);
+	remove_unused_bufs(port->in_vq);
 	spin_unlock_irq(&port->inbuf_lock);
 
 	spin_lock_irq(&port->outvq_lock);
 	reclaim_consumed_buffers(port);
+	remove_unused_bufs(port->out_vq);
 	spin_unlock_irq(&port->outvq_lock);
 }
 
@@ -1938,11 +1948,9 @@ static void remove_vqs(struct ports_device *portdev)
 	struct virtqueue *vq;
 
 	virtio_device_for_each_vq(portdev->vdev, vq) {
-		struct port_buffer *buf;
 
 		flush_bufs(vq, true);
-		while ((buf = virtqueue_detach_unused_buf(vq)))
-			free_buf(buf, true);
+		remove_unused_bufs(vq);
 	}
 	portdev->vdev->config->del_vqs(portdev->vdev);
 	kfree(portdev->in_vqs);
-- 
2.21.0

This patch makes packed ring code compatible with split ring in function
'virtqueue_detach_unused_buf_*'.

Signed-off-by: Pankaj Gupta <pagupta at redhat.com>
---
 drivers/virtio/virtio_ring.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index c8be1c4f5b55..1b98a6777b7e 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1534,6 +1534,11 @@ static void *virtqueue_detach_unused_buf_packed(struct
virtqueue *_vq)
 	for (i = 0; i < vq->packed.vring.num; i++) {
 		if (!vq->packed.desc_state[i].data)
 			continue;
+		vq->packed.next_avail_idx--;
+		if (vq->packed.next_avail_idx < 0) {
+			vq->packed.next_avail_idx = vq->packed.vring.num - 1;
+			vq->packed.avail_wrap_counter ^= 1;
+		}
 		/* detach_buf clears data, so grab it now. */
 		buf = vq->packed.desc_state[i].data;
 		detach_buf_packed(vq, i, NULL);
-- 
2.21.0

On Thu, Aug 08, 2019 at 05:06:05PM +0530, Pankaj Gupta
wrote:
>   The commit a7a69ec0d8e4 ("virtio_console: free buffers after
reset")
>   deferred detaching of unused buffer to virtio device unplug time.
> 
>   This causes unplug/replug of single port in virtio device with an
>   error "Error allocating inbufs\n". As we don't free the
unused buffers
>   attached with the port. Re-plug the same port tries to allocate new
>   buffers in virtqueue and results in this error if queue is full.
> 
>   This patch removes the unused buffers in vq's when we unplug the
port.
>   This is the best we can do as we cannot call device_reset because virtio
>   device is still active.
Why is this indented?
> 
> Reported-by: Xiaohui Li <xiaohli at redhat.com>
> Fixes: b3258ff1d6 ("virtio_console: free buffers after reset")
Fixes: b3258ff1d608 ("virtio: Decrement avail idx on buffer detach")

is the correct format to use.

And given that this is from 2.6.39 (and 2.6.38.5), shouldn't it also be
backported for the stable kernels?

thanks,

greg k-h

On Thu, Aug 08, 2019 at 05:06:06PM +0530, Pankaj Gupta
wrote:
> This patch makes packed ring code compatible with split ring in function
> 'virtqueue_detach_unused_buf_*'.
What does that mean?  What does this "fix"?

thanks,

greg k-h