From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43461) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZHD7k-000777-2F for qemu-devel@nongnu.org; Mon, 20 Jul 2015 11:37:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZHD7i-0003ep-WD for qemu-devel@nongnu.org; Mon, 20 Jul 2015 11:37:00 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38575) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZHD7i-0003el-Qx for qemu-devel@nongnu.org; Mon, 20 Jul 2015 11:36:58 -0400 Date: Mon, 20 Jul 2015 18:36:54 +0300 From: "Michael S. Tsirkin" Message-ID: <20150720183524-mutt-send-email-mst@redhat.com> References: <55AD1072.7030706@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55AD1072.7030706@suse.com> Subject: Re: [Qemu-devel] [RFC PATCH] Fix hotplug/hotunplug issue about virtio 1.0 devices List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Lin Ma Cc: "kraxel@redhat.com >> Gerd Hoffmann" , "qemu-devel@nongnu.org Developers" On Mon, Jul 20, 2015 at 11:14:58PM +0800, Lin Ma wrote: > Hi Michael and Gerd, > > I found an hotplug/hotunplug issue about virtio 1.0 devices and trying to > fix it. > The bug description is: > (qemu) device_add virtio-gpu-pci,id=gpu0 > (qemu) device_del gpu0 At this point, you must wait for guest to ack device removal. > (qemu) device_add virtio-gpu-pci,id=gpu0 > Duplicate ID 'gpu0' for device > Try "help device_add" for more information > > My fix looks like this: > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c > index 283401a..098fc83 100644 > --- a/hw/virtio/virtio-pci.c > +++ b/hw/virtio/virtio-pci.c > @@ -1413,6 +1413,12 @@ static void > virtio_pci_modern_region_map(VirtIOPCIProxy *proxy, > virtio_pci_add_mem_cap(proxy, cap); > } > > +static void virtio_pci_modern_region_unmap(VirtIOPCIProxy *proxy, > + VirtIOPCIRegion *region) > +{ > + memory_region_del_subregion(&proxy->modern_bar, ®ion->mr); > +} > + > /* This is called by virtio-bus just after the device is plugged. */ > static void virtio_pci_device_plugged(DeviceState *d, Error **errp) > { > @@ -1584,6 +1590,16 @@ static void virtio_pci_exit(PCIDevice *pci_dev) > > msix_uninit_exclusive_bar(pci_dev); > address_space_destroy(&proxy->modern_as); > + object_unparent(OBJECT(&proxy->modern_cfg)); > + > + bool modern = !(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_MODERN); > + if (modern) { > + virtio_pci_modern_region_unmap(proxy, &proxy->common); > + virtio_pci_modern_region_unmap(proxy, &proxy->isr); > + virtio_pci_modern_region_unmap(proxy, &proxy->device); > + virtio_pci_modern_region_unmap(proxy, &proxy->notify); > + } > + memory_region_unref(&proxy->modern_bar); > } > > static void virtio_pci_reset(DeviceState *qdev) > > > > But after applying the fix, I got the following errors: > (qemu) device_add virtio-gpu-pci,id=gpu0 > (qemu) device_del gpu0 > (qemu) ** > ERROR:qom/object.c:825:object_unref: assertion failed: (obj->ref > 0) > ...... > > > I think because of the grace period of rcu, the function > memory_region_unref(as->root) in do_address_space_destroy isn't performed > immediately, > The do_address_space_destroy is always performed after virtio_pci_exit, That > caused 'assertion failed: (obj->ref > 0)'. > I have no idea whether my guess is correct or in correct, and don't know how > to avoid this assertion failure in this situation. > Does my fix make sense ? May I have your ideas or suggestions? > > Thanks! > Lin