3.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Alex Williamson <alex.williamson@xxxxxxxxxx> commit 811642d8d8a82c0cce8dc2debfdaf23c5a144839 upstream. If vfio_iommu_group_notifier() acquires a group reference and that reference becomes the last reference to the group, then vfio_group_put introduces a deadlock code path where we're trying to unregister from the iommu notifier chain from within a callout of that chain. Use a work_struct to release this reference asynchronously. Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx> Reviewed-by: Eric Auger <eric.auger@xxxxxxxxxx> Tested-by: Eric Auger <eric.auger@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/vfio/vfio.c | 37 ++++++++++++++++++++++++++++++++++++- 1 file changed, 36 insertions(+), 1 deletion(-) --- a/drivers/vfio/vfio.c +++ b/drivers/vfio/vfio.c @@ -278,6 +278,34 @@ static void vfio_group_put(struct vfio_g kref_put_mutex(&group->kref, vfio_group_release, &vfio.group_lock); } +struct vfio_group_put_work { + struct work_struct work; + struct vfio_group *group; +}; + +static void vfio_group_put_bg(struct work_struct *work) +{ + struct vfio_group_put_work *do_work; + + do_work = container_of(work, struct vfio_group_put_work, work); + + vfio_group_put(do_work->group); + kfree(do_work); +} + +static void vfio_group_schedule_put(struct vfio_group *group) +{ + struct vfio_group_put_work *do_work; + + do_work = kmalloc(sizeof(*do_work), GFP_KERNEL); + if (WARN_ON(!do_work)) + return; + + INIT_WORK(&do_work->work, vfio_group_put_bg); + do_work->group = group; + schedule_work(&do_work->work); +} + /* Assume group_lock or group reference is held */ static void vfio_group_get(struct vfio_group *group) { @@ -553,7 +581,14 @@ static int vfio_iommu_group_notifier(str break; } - vfio_group_put(group); + /* + * If we're the last reference to the group, the group will be + * released, which includes unregistering the iommu group notifier. + * We hold a read-lock on that notifier list, unregistering needs + * a write-lock... deadlock. Release our reference asynchronously + * to avoid that situation. + */ + vfio_group_schedule_put(group); return NOTIFY_OK; }