> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Friday, May 6, 2022 8:25 AM
>
> Now that everything is fully locked there is no need for container_users
> to remain as an atomic, change it to an unsigned int.
>
> Use 'if (group->container)' as the test to determine if the container is
> present or not instead of using container_users.
>
> Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> ---
> drivers/vfio/vfio.c | 28 +++++++++++++---------------
> 1 file changed, 13 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index 94ab415190011d..5c9f56d05f9dfa 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -66,7 +66,7 @@ struct vfio_group {
> struct device dev;
> struct cdev cdev;
> refcount_t users;
> - atomic_t container_users;
> + unsigned int container_users;
> struct iommu_group *iommu_group;
> struct vfio_container *container;
> struct list_head device_list;
> @@ -431,7 +431,7 @@ static void vfio_group_put(struct vfio_group *group)
> * properly hold the group reference.
> */
> WARN_ON(!list_empty(&group->device_list));
> - WARN_ON(atomic_read(&group->container_users));
> + WARN_ON(group->container || group->container_users);
> WARN_ON(group->notifier.head);
>
> list_del(&group->vfio_next);
> @@ -949,6 +949,7 @@ static void __vfio_group_unset_container(struct
> vfio_group *group)
> iommu_group_release_dma_owner(group->iommu_group);
>
> group->container = NULL;
> + group->container_users = 0;
> wake_up(&group->container_q);
> list_del(&group->container_next);
>
> @@ -973,17 +974,13 @@ static void __vfio_group_unset_container(struct
> vfio_group *group)
> */
> static int vfio_group_unset_container(struct vfio_group *group)
> {
> - int users = atomic_cmpxchg(&group->container_users, 1, 0);
> -
> lockdep_assert_held_write(&group->group_rwsem);
>
> - if (!users)
> + if (!group->container)
> return -EINVAL;
> - if (users != 1)
> + if (group->container_users != 1)
> return -EBUSY;
> -
> __vfio_group_unset_container(group);
> -
> return 0;
> }
>
> @@ -996,7 +993,7 @@ static int vfio_group_set_container(struct vfio_group
> *group, int container_fd)
>
> lockdep_assert_held_write(&group->group_rwsem);
>
> - if (atomic_read(&group->container_users))
> + if (group->container || WARN_ON(group->container_users))
> return -EINVAL;
>
> if (group->type == VFIO_NO_IOMMU && !capable(CAP_SYS_RAWIO))
> @@ -1040,12 +1037,12 @@ static int vfio_group_set_container(struct
> vfio_group *group, int container_fd)
> }
>
> group->container = container;
> + group->container_users = 1;
> container->noiommu = (group->type == VFIO_NO_IOMMU);
> list_add(&group->container_next, &container->group_list);
>
> /* Get a reference on the container and mark a user within the group
> */
> vfio_container_get(container);
> - atomic_inc(&group->container_users);
>
> unlock_out:
> up_write(&container->group_lock);
> @@ -1067,8 +1064,8 @@ static int vfio_device_assign_container(struct
> vfio_device *device)
>
> lockdep_assert_held_write(&group->group_rwsem);
>
> - if (0 == atomic_read(&group->container_users) ||
> - !group->container->iommu_driver)
> + if (!group->container || !group->container->iommu_driver ||
> + WARN_ON(!group->container_users))
> return -EINVAL;
>
> if (group->type == VFIO_NO_IOMMU) {
> @@ -1080,14 +1077,15 @@ static int vfio_device_assign_container(struct
> vfio_device *device)
> }
>
> get_file(group->singleton_file);
> - atomic_inc(&group->container_users);
> + group->container_users++;
> return 0;
> }
>
> static void vfio_device_unassign_container(struct vfio_device *device)
> {
> down_write(&device->group->group_rwsem);
> - atomic_dec(&device->group->container_users);
> + WARN_ON(device->group->container_users <= 1);
> + device->group->container_users--;
> fput(device->group->singleton_file);
> up_write(&device->group->group_rwsem);
> }
> @@ -1308,7 +1306,7 @@ static int vfio_group_fops_release(struct inode
> *inode, struct file *filep)
> /* All device FDs must be released before the group fd releases. */
> WARN_ON(group->notifier.head);
> if (group->container) {
> - WARN_ON(atomic_read(&group->container_users) != 1);
> + WARN_ON(group->container_users != 1);
> __vfio_group_unset_container(group);
> }
> group->singleton_file = NULL;
> --
> 2.36.0
