[PATCH v3 0/3] virtio: fix callback synchronization and avq cleanup on reset

["Michael S. Tsirkin" <mst@redhat.com>]

Two issues with virtio device reset:

1. Karl Mehltretter reported that virtio_reset_device() promises
   callbacks are not in progress after reset, but only PCI transports
   actually synchronize callbacks - other transports leave a window
   where a handler already executing keeps running while the driver
   tears down state.

2. sashiko reported a race in virtio_pci_modern: the avq interrupt
   handler calls virtqueue_get_buf concurrently with
   virtqueue_detach_unused_buf in vp_modern_avq_cleanup, and there
   is no synchronize_irq between reset and cleanup.

Fix 1 by adding virtio_synchronize_cbs in the core after reset,
then dropping the now-redundant per-transport sync calls. Fix 2 by
moving avq cleanup from vp_reset to vp_del_vqs, which runs after
callbacks have been synchronized - and is where buffer teardown
conceptually belongs.

Changes v2->v3:
    patch 1: unchanged
    patch 2: split from v2 patch 2 - legacy part only
    patch 3: new - v2 just dropped the sync from modern vp_reset,
        leaving avq_cleanup there before the removed sync. v3
        moves avq_cleanup out of vp_reset entirely into vp_del_vqs,
        fixing the race. Adds NULL check for admin_vq.info needed
        because find_vqs error paths call vp_del_vqs before it is
        allocated.

Michael S. Tsirkin (3):
  virtio: synchronize callbacks after device reset
  virtio_pci_legacy: drop callback sync on reset
  virtio_pci_modern: move avq cleanup from reset to del_vqs

 drivers/virtio/virtio.c            |  2 ++
 drivers/virtio/virtio_pci_common.c |  2 ++
 drivers/virtio/virtio_pci_common.h |  1 +
 drivers/virtio/virtio_pci_legacy.c |  2 --
 drivers/virtio/virtio_pci_modern.c | 10 ++++------
 5 files changed, 9 insertions(+), 8 deletions(-)

-- 
MST