| Message ID | 20240618121958.88673-1-thuth@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | hw/virtio: Fix the de-initialization of vhost-user devices | expand |
On Tue, 18 Jun 2024 15:19, Thomas Huth <thuth@redhat.com> wrote: >The unrealize functions of the various vhost-user devices are >calling the corresponding vhost_*_set_status() functions with a >status of 0 to shut down the device correctly. > >Now these vhost_*_set_status() functions all follow this scheme: > > bool should_start = virtio_device_should_start(vdev, status); > > if (vhost_dev_is_started(&vvc->vhost_dev) == should_start) { > return; > } > > if (should_start) { > /* ... do the initialization stuff ... */ > } else { > /* ... do the cleanup stuff ... */ > } > >The problem here is virtio_device_should_start(vdev, 0) currently >always returns "true" since it internally only looks at vdev->started >instead of looking at the "status" parameter. Thus once the device >got started once, virtio_device_should_start() always returns true virtio_device_should_start() returning true if it's already started and running looks like a code smell to me... it intuitively feels like a ternary state instead of boolean: not startable, startable, already started. >and thus the vhost_*_set_status() functions return early, without >ever doing any clean-up when being called with status == 0. This >causes e.g. problems when trying to hot-plug and hot-unplug a vhost >user devices multiple times since the de-initialization step is >completely skipped during the unplug operation. > >This bug has been introduced in commit 9f6bcfd99f ("hw/virtio: move >vm_running check to virtio_device_started") which replaced > > should_start = status & VIRTIO_CONFIG_S_DRIVER_OK; > >with > > should_start = virtio_device_started(vdev, status); > >which later got replaced by virtio_device_should_start(). This blocked >the possibility to set should_start to false in case the status flag >VIRTIO_CONFIG_S_DRIVER_OK was not set. > >Fix it by adjusting the virtio_device_should_start() function to >only consider the status flag instead of vdev->started. Since this >function is only used in the various vhost_*_set_status() functions >for exactly the same purpose, it should be fine to fix it in this >central place there without any risk to change the behavior of other >code. > >Fixes: 9f6bcfd99f ("hw/virtio: move vm_running check to virtio_device_started") >Buglink: https://issues.redhat.com/browse/RHEL-40708 >Signed-off-by: Thomas Huth <thuth@redhat.com> >--- Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h index 7d5ffdc145..2eafad17b8 100644 --- a/include/hw/virtio/virtio.h +++ b/include/hw/virtio/virtio.h @@ -470,9 +470,9 @@ static inline bool virtio_device_started(VirtIODevice *vdev, uint8_t status) * @vdev - the VirtIO device * @status - the devices status bits * - * This is similar to virtio_device_started() but also encapsulates a - * check on the VM status which would prevent a device starting - * anyway. + * This is similar to virtio_device_started() but ignores vdev->started + * and also encapsulates a check on the VM status which would prevent a + * device from starting anyway. */ static inline bool virtio_device_should_start(VirtIODevice *vdev, uint8_t status) { @@ -480,7 +480,7 @@ static inline bool virtio_device_should_start(VirtIODevice *vdev, uint8_t status return false; } - return virtio_device_started(vdev, status); + return status & VIRTIO_CONFIG_S_DRIVER_OK; } static inline void virtio_set_started(VirtIODevice *vdev, bool started)
The unrealize functions of the various vhost-user devices are calling the corresponding vhost_*_set_status() functions with a status of 0 to shut down the device correctly. Now these vhost_*_set_status() functions all follow this scheme: bool should_start = virtio_device_should_start(vdev, status); if (vhost_dev_is_started(&vvc->vhost_dev) == should_start) { return; } if (should_start) { /* ... do the initialization stuff ... */ } else { /* ... do the cleanup stuff ... */ } The problem here is virtio_device_should_start(vdev, 0) currently always returns "true" since it internally only looks at vdev->started instead of looking at the "status" parameter. Thus once the device got started once, virtio_device_should_start() always returns true and thus the vhost_*_set_status() functions return early, without ever doing any clean-up when being called with status == 0. This causes e.g. problems when trying to hot-plug and hot-unplug a vhost user devices multiple times since the de-initialization step is completely skipped during the unplug operation. This bug has been introduced in commit 9f6bcfd99f ("hw/virtio: move vm_running check to virtio_device_started") which replaced should_start = status & VIRTIO_CONFIG_S_DRIVER_OK; with should_start = virtio_device_started(vdev, status); which later got replaced by virtio_device_should_start(). This blocked the possibility to set should_start to false in case the status flag VIRTIO_CONFIG_S_DRIVER_OK was not set. Fix it by adjusting the virtio_device_should_start() function to only consider the status flag instead of vdev->started. Since this function is only used in the various vhost_*_set_status() functions for exactly the same purpose, it should be fine to fix it in this central place there without any risk to change the behavior of other code. Fixes: 9f6bcfd99f ("hw/virtio: move vm_running check to virtio_device_started") Buglink: https://issues.redhat.com/browse/RHEL-40708 Signed-off-by: Thomas Huth <thuth@redhat.com> --- include/hw/virtio/virtio.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)