From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH] virtio_console: allocate inbufs in add_port() only if it is needed Date: Wed, 6 Nov 2019 10:03:02 -0500 Message-ID: <20191106095707-mutt-send-email-mst__15314.5123085537$1573052604$gmane$org@kernel.org> References: <20191018164718.15999-1-lvivier@redhat.com> <20191106085548-mutt-send-email-mst@kernel.org> <83d88904-1626-8dd6-9e5c-7abcee27bcd0@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <83d88904-1626-8dd6-9e5c-7abcee27bcd0@redhat.com> 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: Laurent Vivier 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 Wed, Nov 06, 2019 at 03:02:25PM +0100, Laurent Vivier wrote: > 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 Oh I see. However it's a bit asymmetrical to special case ring full. How about making fill_queue return int and testing return code for -ENOSPC instead? Will also help propagate errors correctly. And I guess CC stable? -- MST