From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34960) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZHQGD-0005J5-BL for qemu-devel@nongnu.org; Tue, 21 Jul 2015 01:38:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZHQG9-0002yF-AM for qemu-devel@nongnu.org; Tue, 21 Jul 2015 01:38:37 -0400 Received: from smtp2.provo.novell.com ([137.65.250.81]:49624) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZHQG9-0002xj-4Z for qemu-devel@nongnu.org; Tue, 21 Jul 2015 01:38:33 -0400 Message-ID: <55ADDA91.6030405@suse.com> Date: Tue, 21 Jul 2015 13:37:21 +0800 From: Lin Ma MIME-Version: 1.0 References: <55AD1072.7030706@suse.com> <20150720183524-mutt-send-email-mst@redhat.com> In-Reply-To: <20150720183524-mutt-send-email-mst@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [RFC PATCH] Fix hotplug/hotunplug issue about virtio 1.0 devices Reply-To: lma@suse.com List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: "kraxel@redhat.com >> Gerd Hoffmann" , "qemu-devel@nongnu.org Developers" 在 2015年07月20日 23:36, Michael S. Tsirkin 写道: > 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. After removing the device from qmp, The DEVICE_DELETED async event was shown. So the guest already acked, Then add a device with same id, It always reports 'Duplicate ID ...'. The device was completely removed from guest, But still in object list of qemu. > > >> (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 >