[PATCH v3 0/2] virtio_console: fix replug of virtio console port

[PATCH v3 0/2] virtio_console: fix replug of virtio console port

[Pankaj Gupta]

This patch series fixes the issue with unplug/replug of a port in virtio
console driver which fails with an error "Error allocating inbufs\n".
Patch 1 makes use of 'virtqueue_detach_unused_buf' function to detach
the unused buffers during port hotunplug time.
Patch 2 updates the next avail index for packed ring code.
Tested the packed ring code with the qemu virtio 1.1 device code posted
here [1].

Changes from v2
 Better change log in patch2 - [Greg]
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: decrement avail idx with buffer detach for packed ring

 char/virtio_console.c |   14 +++++++++++---
 virtio/virtio_ring.c  |    6 ++++++
 2 files changed, 17 insertions(+), 3 deletions(-)
-- 
2.21.0

[PATCH v3 1/2] virtio_console: free unused buffers with port delete

[Pankaj Gupta]

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@redhat.com>
Fixes: a7a69ec0d8e4 ("virtio_console: free buffers after reset")
Cc: stable@vger.kernel.org
Signed-off-by: Pankaj Gupta <pagupta@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

[PATCH v3 2/2] virtio: decrement avail idx with buffer detach for packed ring

[Pankaj Gupta]

This patch decrements 'next_avail_idx' count when detaching a buffer
from vq for packed ring code. Split ring code already does this in
virtqueue_detach_unused_buf_split function. This updates the
'next_avail_idx' to the previous correct index after an unused buffer
is detatched from the vq.

Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
---
 drivers/virtio/virtio_ring.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index c8be1c4f5b55..7c69181113e2 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1537,6 +1537,12 @@ static void *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq)
 		/* detach_buf clears data, so grab it now. */
 		buf = vq->packed.desc_state[i].data;
 		detach_buf_packed(vq, i, NULL);
+		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;
+		}
+
 		END_USE(vq);
 		return buf;
 	}
-- 
2.20.1

Re: [PATCH v3 2/2] virtio: decrement avail idx with buffer detach for packed ring

[Michael S. Tsirkin]

On Fri, Aug 09, 2019 at 12:18:47PM +0530, Pankaj Gupta wrote:
> This patch decrements 'next_avail_idx' count when detaching a buffer
> from vq for packed ring code. Split ring code already does this in
> virtqueue_detach_unused_buf_split function. This updates the
> 'next_avail_idx' to the previous correct index after an unused buffer
> is detatched from the vq.
> 
> Signed-off-by: Pankaj Gupta <pagupta@redhat.com>

I would make this patch 1, not patch 2, otherwise
patch 1 corrupts the ring.


> ---
>  drivers/virtio/virtio_ring.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index c8be1c4f5b55..7c69181113e2 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -1537,6 +1537,12 @@ static void *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq)
>  		/* detach_buf clears data, so grab it now. */
>  		buf = vq->packed.desc_state[i].data;
>  		detach_buf_packed(vq, i, NULL);
> +		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;
> +		}
> +
>  		END_USE(vq);
>  		return buf;
>  	}
> -- 
> 2.20.1

Re: [PATCH v3 2/2] virtio: decrement avail idx with buffer detach for packed ring

[Pankaj Gupta]

> On Fri, Aug 09, 2019 at 12:18:47PM +0530, Pankaj Gupta wrote:
> > This patch decrements 'next_avail_idx' count when detaching a buffer
> > from vq for packed ring code. Split ring code already does this in
> > virtqueue_detach_unused_buf_split function. This updates the
> > 'next_avail_idx' to the previous correct index after an unused buffer
> > is detatched from the vq.
> > 
> > Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
> 
> I would make this patch 1, not patch 2, otherwise
> patch 1 corrupts the ring.

Sure. Will post this patch as patch 1 in next version.

Thanks,
Pankaj 

> 
> 
> > ---
> >  drivers/virtio/virtio_ring.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index c8be1c4f5b55..7c69181113e2 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -1537,6 +1537,12 @@ static void
> > *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq)
> >  		/* detach_buf clears data, so grab it now. */
> >  		buf = vq->packed.desc_state[i].data;
> >  		detach_buf_packed(vq, i, NULL);
> > +		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;
> > +		}
> > +
> >  		END_USE(vq);
> >  		return buf;
> >  	}
> > --
> > 2.20.1
> 

Re: [PATCH v3 2/2] virtio: decrement avail idx with buffer detach for packed ring

[Jason Wang]

On 2019/8/9 下午2:48, Pankaj Gupta wrote:
> This patch decrements 'next_avail_idx' count when detaching a buffer
> from vq for packed ring code. Split ring code already does this in
> virtqueue_detach_unused_buf_split function. This updates the
> 'next_avail_idx' to the previous correct index after an unused buffer
> is detatched from the vq.
>
> Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
> ---
>   drivers/virtio/virtio_ring.c | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index c8be1c4f5b55..7c69181113e2 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -1537,6 +1537,12 @@ static void *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq)
>   		/* detach_buf clears data, so grab it now. */
>   		buf = vq->packed.desc_state[i].data;
>   		detach_buf_packed(vq, i, NULL);
> +		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;
> +		}
> +
>   		END_USE(vq);
>   		return buf;
>   	}


Acked-by: Jason Wang <jasowang@redhat.com>


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Re: [PATCH v3 2/2] virtio: decrement avail idx with buffer detach for packed ring

[Pankaj Gupta]

> 
> On 2019/8/9 下午2:48, Pankaj Gupta wrote:
> > This patch decrements 'next_avail_idx' count when detaching a buffer
> > from vq for packed ring code. Split ring code already does this in
> > virtqueue_detach_unused_buf_split function. This updates the
> > 'next_avail_idx' to the previous correct index after an unused buffer
> > is detatched from the vq.
> >
> > Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
> > ---
> >   drivers/virtio/virtio_ring.c | 6 ++++++
> >   1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index c8be1c4f5b55..7c69181113e2 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -1537,6 +1537,12 @@ static void
> > *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq)
> >   		/* detach_buf clears data, so grab it now. */
> >   		buf = vq->packed.desc_state[i].data;
> >   		detach_buf_packed(vq, i, NULL);
> > +		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;
> > +		}
> > +
> >   		END_USE(vq);
> >   		return buf;
> >   	}
> 
> 
> Acked-by: Jason Wang <jasowang@redhat.com>

Thank you, Jason.

Best regards,
Pankaj

> 
> 
> 
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Re: [PATCH v3 1/2] virtio_console: free unused buffers with port delete

[Michael S. Tsirkin]

On Fri, Aug 09, 2019 at 12:18:46PM +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.

So why not reuse the buffers that are already there in this case?
Seems quite possible.

> 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@redhat.com>
> Fixes: a7a69ec0d8e4 ("virtio_console: free buffers after reset")
> Cc: stable@vger.kernel.org
> Signed-off-by: Pankaj Gupta <pagupta@redhat.com>

This is really a revert of a7a69ec0d8e4, just tagged confusingly.

And the original is also supposed to be a bugfix.
So how will the original bug be fixed?

"this is the best we can do" is rarely the case.

I am not necessarily against the revert. But if we go that way then what
we need to do is specify the behaviour in the spec, since strict spec
compliance is exactly what the original patch was addressing.

In particular, we'd document that console has a special property that
when port is detached virtqueue is considered stopped, device must not
use any buffers, and it is legal to take buffers out of the device.



> ---
>  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

Re: [PATCH v3 1/2] virtio_console: free unused buffers with port delete

[Pankaj Gupta]

> 
> On Fri, Aug 09, 2019 at 12:18:46PM +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.
> 
> So why not reuse the buffers that are already there in this case?
> Seems quite possible.

I took this approach because reusing the buffers will involve tweaking
the existing core functionality like managing the the virt queue indexes.
Compared to that deleting the buffers while hot-unplugging port is simple
and was working fine before. It seems logically correct as well.   

I agree we need a spec change for this.

> 
> > 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@redhat.com>
> > Fixes: a7a69ec0d8e4 ("virtio_console: free buffers after reset")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
> 
> This is really a revert of a7a69ec0d8e4, just tagged confusingly.
> 
> And the original is also supposed to be a bugfix.
> So how will the original bug be fixed?

Yes, Even I was confused while adding this tag.
I will remove remove 'fixes' tag completely for this patch?
because its a revert to original behavior which also is a bugfix.

> 
> "this is the best we can do" is rarely the case.
> 
> I am not necessarily against the revert. But if we go that way then what
> we need to do is specify the behaviour in the spec, since strict spec
> compliance is exactly what the original patch was addressing.

Agree.

> 
> In particular, we'd document that console has a special property that
> when port is detached virtqueue is considered stopped, device must not
> use any buffers, and it is legal to take buffers out of the device.

Yes. This documents the exact scenario. Thanks.
You want me to send a patch for the spec change?

Best regards,
Pankaj
 
> 
> 
> 
> > ---
> >  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
> 

Re: [PATCH v3 1/2] virtio_console: free unused buffers with port delete

[Michael S. Tsirkin]

On Mon, Aug 12, 2019 at 01:36:48AM -0400, Pankaj Gupta wrote:
> 
> > 
> > On Fri, Aug 09, 2019 at 12:18:46PM +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.
> > 
> > So why not reuse the buffers that are already there in this case?
> > Seems quite possible.
> 
> I took this approach because reusing the buffers will involve tweaking
> the existing core functionality like managing the the virt queue indexes.

I don't see why frankly, if you keep a list of outstanding
buffers on plug you can assume they have been added.

> Compared to that deleting the buffers while hot-unplugging port is simple
> and was working fine before. It seems logically correct as well.   
> 
> I agree we need a spec change for this.
> 
> > 
> > > 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@redhat.com>
> > > Fixes: a7a69ec0d8e4 ("virtio_console: free buffers after reset")
> > > Cc: stable@vger.kernel.org
> > > Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
> > 
> > This is really a revert of a7a69ec0d8e4, just tagged confusingly.
> > 
> > And the original is also supposed to be a bugfix.
> > So how will the original bug be fixed?
> 
> Yes, Even I was confused while adding this tag.
> I will remove remove 'fixes' tag completely for this patch?
> because its a revert to original behavior which also is a bugfix.
> 
> > 
> > "this is the best we can do" is rarely the case.
> > 
> > I am not necessarily against the revert. But if we go that way then what
> > we need to do is specify the behaviour in the spec, since strict spec
> > compliance is exactly what the original patch was addressing.
> 
> Agree.
> 
> > 
> > In particular, we'd document that console has a special property that
> > when port is detached virtqueue is considered stopped, device must not
> > use any buffers, and it is legal to take buffers out of the device.
> 
> Yes. This documents the exact scenario. Thanks.
> You want me to send a patch for the spec change?
> 
> Best regards,
> Pankaj

Go ahead.

> > 
> > 
> > 
> > > ---
> > >  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
> >