From mboxrd@z Thu Jan 1 00:00:00 1970 From: Laurent Vivier Subject: Re: [PATCH] virtio_console: allocate inbufs in add_port() only if it is needed Date: Wed, 6 Nov 2019 15:02:25 +0100 Message-ID: <83d88904-1626-8dd6-9e5c-7abcee27bcd0__24330.2077915118$1573048977$gmane$org@redhat.com> References: <20191018164718.15999-1-lvivier@redhat.com> <20191106085548-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: <20191106085548-mutt-send-email-mst@kernel.org> Content-Language: en-US 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: Greg Kroah-Hartman , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Arnd Bergmann , Amit Shah List-Id: virtualization@lists.linuxfoundation.org On 06/11/2019 14:56, Michael S. Tsirkin wrote: > On Fri, Oct 18, 2019 at 06:47:18PM +0200, Laurent Vivier wrote: >> When we hot unplug a virtserialport and then try to hot plug again, >> it fails: >> >> (qemu) chardev-add socket,id=serial0,path=/tmp/serial0,server,nowait >> (qemu) device_add virtserialport,bus=virtio-serial0.0,nr=2,\ >> chardev=serial0,id=serial0,name=serial0 >> (qemu) device_del serial0 >> (qemu) device_add virtserialport,bus=virtio-serial0.0,nr=2,\ >> chardev=serial0,id=serial0,name=serial0 >> kernel error: >> virtio-ports vport2p2: Error allocating inbufs >> qemu error: >> virtio-serial-bus: Guest failure in adding port 2 for device \ >> virtio-serial0.0 >> >> This happens because buffers for the in_vq are allocated when the port is >> added but are not released when the port is unplugged. >> >> They are only released when virtconsole is removed (see a7a69ec0d8e4) >> >> To avoid the problem and to be symmetric, we could allocate all the buffers >> in init_vqs() as they are released in remove_vqs(), but it sounds like >> a waste of memory. >> >> Rather than that, this patch changes add_port() logic to only allocate the >> buffers if the in_vq has available free slots. >> >> Fixes: a7a69ec0d8e4 ("virtio_console: free buffers after reset") >> Cc: mst@redhat.com >> Signed-off-by: Laurent Vivier >> --- >> drivers/char/virtio_console.c | 17 +++++++++++------ >> 1 file changed, 11 insertions(+), 6 deletions(-) >> >> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c >> index 7270e7b69262..77105166fe01 100644 >> --- a/drivers/char/virtio_console.c >> +++ b/drivers/char/virtio_console.c >> @@ -1421,12 +1421,17 @@ static int add_port(struct ports_device *portdev, u32 id) >> spin_lock_init(&port->outvq_lock); >> init_waitqueue_head(&port->waitqueue); >> >> - /* Fill the in_vq with buffers so the host can send us data. */ >> - nr_added_bufs = fill_queue(port->in_vq, &port->inbuf_lock); >> - if (!nr_added_bufs) { >> - dev_err(port->dev, "Error allocating inbufs\n"); >> - err = -ENOMEM; >> - goto free_device; >> + /* if the in_vq has not already been filled (the port has already been >> + * used and unplugged), fill the in_vq with buffers so the host can >> + * send us data. >> + */ >> + if (port->in_vq->num_free != 0) { >> + nr_added_bufs = fill_queue(port->in_vq, &port->inbuf_lock); >> + if (!nr_added_bufs) { >> + dev_err(port->dev, "Error allocating inbufs\n"); >> + err = -ENOMEM; >> + goto free_device; >> + } >> } >> >> if (is_rproc_serial(port->portdev->vdev)) > > Well fill_queue will just add slots as long as it can. > So on a full queue it does nothing. How does this patch help? Yes, but in this case it returns 0 and so add_port() fails and exits with -ENOMEM and the device is freed. It's what this patch tries to avoid. Thanks, Laurent