From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pankaj Gupta Subject: Re: [PATCH v3 1/2] virtio_console: free unused buffers with port delete Date: Mon, 12 Aug 2019 01:36:48 -0400 (EDT) Message-ID: <361928616.7829318.1565588208467.JavaMail.zimbra@redhat.com> References: <20190809064847.28918-1-pagupta@redhat.com> <20190809064847.28918-2-pagupta@redhat.com> <20190810141019-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190810141019-mutt-send-email-mst@kernel.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "Michael S. Tsirkin" Cc: arnd@arndb.de, amit@kernel.org, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, xiaohli@redhat.com List-Id: virtualization@lists.linuxfoundation.org > > 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 > > Fixes: a7a69ec0d8e4 ("virtio_console: free buffers after reset") > > Cc: stable@vger.kernel.org > > Signed-off-by: Pankaj Gupta > > 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 >