Re: [PATCH drm-misc-next v3 6/7] drm/gpuvm: generalize dma_resv/extobj handling and GEM validation

Boris Brezillon
2023-09-11T21:59:41Z

On Sat, 9 Sep 2023 17:31:13 +0200
Danilo Krummrich <dakr@redhat.com> wrote:

> +/**
> + * get_next_vm_bo_from_list() - get the next vm_bo element
> + * @__gpuvm: The GPU VM
> + * @__list_name: The name of the list we're iterating on
> + * @__local_list: A pointer to the local list used to store already iterated items
> + * @__prev_vm_bo: The previous element we got from drm_gpuvm_get_next_cached_vm_bo()
> + *
> + * This helper is here to provide lockless list iteration. Lockless as in, the
> + * iterator releases the lock immediately after picking the first element from
> + * the list, so list insertion deletion can happen concurrently.
> + *
> + * Elements popped from the original list are kept in a local list, so removal
> + * and is_empty checks can still happen while we're iterating the list.
> + */
> +#define get_next_vm_bo_from_list(__gpuvm, __list_name, __local_list, __prev_vm_bo) \
> + ({ \
> + struct drm_gpuvm_bo *__vm_bo; \

Missing NULL assignment here.

> + \
> + drm_gpuvm_bo_put(__prev_vm_bo); \
> + \
> + spin_lock(&(__gpuvm)->__list_name.lock); \
> + while (!list_empty(&(__gpuvm)->__list_name.list)) { \
> + __vm_bo = list_first_entry(&(__gpuvm)->__list_name.list, \
> + struct drm_gpuvm_bo, \
> + list.entry.__list_name); \
> + if (drm_gpuvm_bo_get_unless_zero(__vm_bo)) { \
> + list_move_tail(&(__vm_bo)->list.entry.__list_name, \
> + __local_list); \
> + break; \
> + } else { \
> + list_del_init(&(__vm_bo)->list.entry.__list_name); \
> + __vm_bo = NULL; \
> + } \
> + } \
> + spin_unlock(&(__gpuvm)->__list_name.lock); \
> + \
> + __vm_bo; \
> + })
> +
> +/**
> + * for_each_vm_bo_in_list() - internal vm_bo list iterator
> + *
> + * This helper is here to provide lockless list iteration. Lockless as in, the
> + * iterator releases the lock immediately after picking the first element from the
> + * list, so list insertion and deletion can happen concurrently.
> + *
> + * Typical use:
> + *
> + * struct drm_gpuvm_bo *vm_bo;
> + * LIST_HEAD(my_local_list);
> + *
> + * ret = 0;
> + * drm_gpuvm_for_each_vm_bo(gpuvm, <list_name>, &my_local_list, vm_bo) {
> + * ret = do_something_with_vm_bo(..., vm_bo);
> + * if (ret)
> + * break;
> + * }
> + * drm_gpuvm_bo_put(vm_bo);
> + * drm_gpuvm_restore_vm_bo_list(gpuvm, <list_name>, &my_local_list);

Might be worth mentioning that the vm_bo pointer shouldn't be
re-assigned from inside for loop, otherwise
the next get_next_vm_bo_from_list() will be passed a wrong prev_vm_bo.

> + *
> + *
> + * Only used for internal list iterations, not meant to be exposed to the outside
> + * world.
> + */
> +#define for_each_vm_bo_in_list(__gpuvm, __list_name, __local_list, __vm_bo) \
> + for (__vm_bo = get_next_vm_bo_from_list(__gpuvm, __list_name, \
> + __local_list, NULL); \
> + __vm_bo; \
> + __vm_bo = get_next_vm_bo_from_list(__gpuvm, __list_name, \
> + __local_list, __vm_bo)) \