On Fri, 20 Jun 2025 16:50:51 -0700
Chia-I Wu <olva...@gmail.com> wrote:
> We would like to access panthor_file from panthor_group on gpu errors.
> Because panthour_group can outlive drm_file, add refcount to
> panthor_file to ensure its lifetime.
I'm not a huge fan of refcounting panthor_file because people tend to
put resource they expect to be released when the last handle goes away,
and if we don't refcount these sub-resources they might live longer
than they are meant to. Also not a huge fan of the circular referencing
that exists between file and groups after this change.
How about we move the process info to a sub-object that's refcounted
and let both panthor_file and panthor_group take a ref on this object
instead?
>
> Signed-off-by: Chia-I Wu <olva...@gmail.com>
> ---
> drivers/gpu/drm/panthor/panthor_device.h | 16 ++++++++++++++++
> drivers/gpu/drm/panthor/panthor_drv.c | 15 ++++++++++++++-
> drivers/gpu/drm/panthor/panthor_mmu.c | 1 +
> drivers/gpu/drm/panthor/panthor_sched.c | 6 ++++++
> 4 files changed, 37 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/panthor/panthor_device.h
> b/drivers/gpu/drm/panthor/panthor_device.h
> index 4fc7cf2aeed57..75ae6fd3a5128 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.h
> +++ b/drivers/gpu/drm/panthor/panthor_device.h
> @@ -256,8 +256,24 @@ struct panthor_file {
>
> /** @stats: cycle and timestamp measures for job execution. */
> struct panthor_gpu_usage stats;
> +
> + /** @refcount: ref count of this file */
> + struct kref refcount;
> };
>
> +static inline struct panthor_file *panthor_file_get(struct panthor_file
> *pfile)
> +{
> + kref_get(&pfile->refcount);
> + return pfile;
> +}
> +
> +void panthor_file_release(struct kref *kref);
> +
> +static inline void panthor_file_put(struct panthor_file *pfile)
> +{
> + kref_put(&pfile->refcount, panthor_file_release);
> +}
> +
> int panthor_device_init(struct panthor_device *ptdev);
> void panthor_device_unplug(struct panthor_device *ptdev);
>
> diff --git a/drivers/gpu/drm/panthor/panthor_drv.c
> b/drivers/gpu/drm/panthor/panthor_drv.c
> index 775a66c394544..aea9609684b77 100644
> --- a/drivers/gpu/drm/panthor/panthor_drv.c
> +++ b/drivers/gpu/drm/panthor/panthor_drv.c
> @@ -1393,6 +1393,16 @@ static int panthor_ioctl_set_user_mmio_offset(struct
> drm_device *ddev,
> return 0;
> }
>
> +void panthor_file_release(struct kref *kref)
> +{
> + struct panthor_file *pfile =
> + container_of(kref, struct panthor_file, refcount);
> +
> + WARN_ON(pfile->vms || pfile->groups);
> +
> + kfree(pfile);
> +}
> +
> static int
> panthor_open(struct drm_device *ddev, struct drm_file *file)
> {
> @@ -1426,6 +1436,8 @@ panthor_open(struct drm_device *ddev, struct drm_file
> *file)
> if (ret)
> goto err_destroy_vm_pool;
>
> + kref_init(&pfile->refcount);
> +
> file->driver_priv = pfile;
> return 0;
>
> @@ -1442,10 +1454,11 @@ panthor_postclose(struct drm_device *ddev, struct
> drm_file *file)
> {
> struct panthor_file *pfile = file->driver_priv;
>
> + /* destroy vm and group handles now to avoid circular references */
> panthor_group_pool_destroy(pfile);
> panthor_vm_pool_destroy(pfile);
>
> - kfree(pfile);
> + panthor_file_put(pfile);
> }
>
> static const struct drm_ioctl_desc panthor_drm_driver_ioctls[] = {
> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c
> b/drivers/gpu/drm/panthor/panthor_mmu.c
> index b39ea6acc6a96..ccbcfe11420ac 100644
> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> @@ -1604,6 +1604,7 @@ void panthor_vm_pool_destroy(struct panthor_file *pfile)
>
> xa_destroy(&pfile->vms->xa);
> kfree(pfile->vms);
> + pfile->vms = NULL;
> }
>
> /**
> diff --git a/drivers/gpu/drm/panthor/panthor_sched.c
> b/drivers/gpu/drm/panthor/panthor_sched.c
> index a2248f692a030..485072904cd7d 100644
> --- a/drivers/gpu/drm/panthor/panthor_sched.c
> +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> @@ -535,6 +535,9 @@ struct panthor_group {
> /** @ptdev: Device. */
> struct panthor_device *ptdev;
>
> + /** @pfile: File this group is created from. */
> + struct panthor_file *pfile;
> +
> /** @vm: VM bound to the group. */
> struct panthor_vm *vm;
>
> @@ -919,6 +922,7 @@ static void group_release_work(struct work_struct *work)
> panthor_kernel_bo_destroy(group->syncobjs);
>
> panthor_vm_put(group->vm);
> + panthor_file_put(group->pfile);
> kfree(group);
> }
>
> @@ -3467,6 +3471,8 @@ int panthor_group_create(struct panthor_file *pfile,
> INIT_WORK(&group->tiler_oom_work, group_tiler_oom_work);
> INIT_WORK(&group->release_work, group_release_work);
>
> + group->pfile = panthor_file_get(pfile);
> +
> group->vm = panthor_vm_pool_get_vm(pfile->vms, group_args->vm_id);
> if (!group->vm) {
> ret = -EINVAL;
