Re: [PATCH V2] drm/buddy: Integrate lockdep annotations for gpu buddy manager

[Arunpravin Paneer Selvam <arunpravin.paneerselvam@amd.com>]

I merged this patch into drm-misc-next branch.

Thanks,
Arun.

On 5/8/2026 12:25 PM, Tejas Upadhyay wrote:
> gpu_buddy APIs are expected to be called with the driver-provided lock
> held, but there is no runtime enforcement of this contract. Add lockdep
> annotations to catch locking violations early.
>
> Introduce gpu_buddy_driver_set_lock() for the driver to register the
> lock that protects the buddy manager. Add gpu_buddy_driver_lock_held()
> assertions to all exported gpu_buddy and drm_buddy APIs that
> access/modify the manager state. The lock_dep_map field is only compiled
> in when CONFIG_LOCKDEP is enabled, adding zero overhead to production
> builds.
>
> Wire up xe_ttm_vram_mgr to register its mutex with the buddy manager
> after initialization.
>
> Assisted-by: Copilot:claude-opus-4.6
> Suggested-by: Matthew Brost <matthew.brost@intel.com>
> Signed-off-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
> Reviewed-by: Matthew Auld <matthew.auld@intel.com>
> ---
>   drivers/gpu/buddy.c                  | 11 ++++++++
>   drivers/gpu/drm/drm_buddy.c          |  1 +
>   drivers/gpu/drm/xe/xe_ttm_vram_mgr.c |  1 +
>   include/linux/gpu_buddy.h            | 41 ++++++++++++++++++++++++++++
>   4 files changed, 54 insertions(+)
>
> diff --git a/drivers/gpu/buddy.c b/drivers/gpu/buddy.c
> index 52686672e99f..eb1457376307 100644
> --- a/drivers/gpu/buddy.c
> +++ b/drivers/gpu/buddy.c
> @@ -437,6 +437,9 @@ int gpu_buddy_init(struct gpu_buddy *mm, u64 size, u64 chunk_size)
>   		root_count++;
>   	} while (size);
>   
> +#ifdef CONFIG_LOCKDEP
> +	mm->lock_dep_map = NULL;
> +#endif
>   	return 0;
>   
>   out_free_roots:
> @@ -538,6 +541,7 @@ void gpu_buddy_reset_clear(struct gpu_buddy *mm, bool is_clear)
>   	unsigned int order;
>   	int i;
>   
> +	gpu_buddy_driver_lock_held(mm);
>   	size = mm->size;
>   	for (i = 0; i < mm->n_roots; ++i) {
>   		order = ilog2(size) - ilog2(mm->chunk_size);
> @@ -580,6 +584,7 @@ EXPORT_SYMBOL(gpu_buddy_reset_clear);
>   void gpu_buddy_free_block(struct gpu_buddy *mm,
>   			  struct gpu_buddy_block *block)
>   {
> +	gpu_buddy_driver_lock_held(mm);
>   	BUG_ON(!gpu_buddy_block_is_allocated(block));
>   	mm->avail += gpu_buddy_block_size(mm, block);
>   	if (gpu_buddy_block_is_clear(block))
> @@ -633,6 +638,7 @@ void gpu_buddy_free_list(struct gpu_buddy *mm,
>   {
>   	bool mark_clear = flags & GPU_BUDDY_CLEARED;
>   
> +	gpu_buddy_driver_lock_held(mm);
>   	__gpu_buddy_free_list(mm, objects, mark_clear, !mark_clear);
>   }
>   EXPORT_SYMBOL(gpu_buddy_free_list);
> @@ -1172,6 +1178,8 @@ int gpu_buddy_block_trim(struct gpu_buddy *mm,
>   	u64 new_start;
>   	int err;
>   
> +	gpu_buddy_driver_lock_held(mm);
> +
>   	if (!list_is_singular(blocks))
>   		return -EINVAL;
>   
> @@ -1287,6 +1295,8 @@ int gpu_buddy_alloc_blocks(struct gpu_buddy *mm,
>   	unsigned long pages;
>   	int err;
>   
> +	gpu_buddy_driver_lock_held(mm);
> +
>   	if (size < mm->chunk_size)
>   		return -EINVAL;
>   
> @@ -1475,6 +1485,7 @@ void gpu_buddy_print(struct gpu_buddy *mm)
>   {
>   	int order;
>   
> +	gpu_buddy_driver_lock_held(mm);
>   	pr_info("chunk_size: %lluKiB, total: %lluMiB, free: %lluMiB, clear_free: %lluMiB\n",
>   		mm->chunk_size >> 10, mm->size >> 20, mm->avail >> 20, mm->clear_avail >> 20);
>   
> diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
> index 841f3de5f307..faa025498de4 100644
> --- a/drivers/gpu/drm/drm_buddy.c
> +++ b/drivers/gpu/drm/drm_buddy.c
> @@ -42,6 +42,7 @@ void drm_buddy_print(struct gpu_buddy *mm, struct drm_printer *p)
>   {
>   	int order;
>   
> +	gpu_buddy_driver_lock_held(mm);
>   	drm_printf(p, "chunk_size: %lluKiB, total: %lluMiB, free: %lluMiB, clear_free: %lluMiB\n",
>   		   mm->chunk_size >> 10, mm->size >> 20, mm->avail >> 20, mm->clear_avail >> 20);
>   
> diff --git a/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c b/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c
> index 6ba47996bc7c..9f67df646955 100644
> --- a/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c
> +++ b/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c
> @@ -322,6 +322,7 @@ int __xe_ttm_vram_mgr_init(struct xe_device *xe, struct xe_ttm_vram_mgr *mgr,
>   	if (err)
>   		return err;
>   
> +	gpu_buddy_driver_set_lock(&mgr->mm, &mgr->lock);
>   	ttm_set_driver_manager(&xe->ttm, mem_type, &mgr->manager);
>   	ttm_resource_manager_set_used(&mgr->manager, true);
>   
> diff --git a/include/linux/gpu_buddy.h b/include/linux/gpu_buddy.h
> index 5fa917ba5450..71941a039648 100644
> --- a/include/linux/gpu_buddy.h
> +++ b/include/linux/gpu_buddy.h
> @@ -154,6 +154,7 @@ struct gpu_buddy_block {
>    * @avail: Total free space currently available for allocation in bytes.
>    * @clear_avail: Free space available in the clear tree (zeroed memory) in bytes.
>    *               This is a subset of @avail.
> + * @lock_dep_map: Annotates gpu_buddy API with a driver provided lock.
>    */
>   struct gpu_buddy {
>   /* private: */
> @@ -179,8 +180,48 @@ struct gpu_buddy {
>   	u64 size;
>   	u64 avail;
>   	u64 clear_avail;
> +#ifdef CONFIG_LOCKDEP
> +	struct lockdep_map *lock_dep_map;
> +#endif
>   };
>   
> +#ifdef CONFIG_LOCKDEP
> +/**
> + * gpu_buddy_driver_set_lock() - Set the lock protecting accesses to GPU BUDDY
> + * @mm: Pointer to GPU buddy structure.
> + * @lock: the lock used to protect the gpu buddy. The locking primitive
> + * must contain a dep_map field.
> + *
> + * Call this to annotate gpu_buddy APIs which access/modify gpu_buddy manager
> + */
> +#define gpu_buddy_driver_set_lock(mm, lock) \
> +	do { \
> +		struct gpu_buddy *__mm = (mm); \
> +		if (!WARN(__mm->lock_dep_map, "GPU BUDDY MM lock should be set only once.")) \
> +			__mm->lock_dep_map = &(lock)->dep_map; \
> +	} while (0)
> +#else
> +#define gpu_buddy_driver_set_lock(mm, lock) do { (void)(mm); (void)(lock); } while (0)
> +#endif
> +
> +#ifdef CONFIG_LOCKDEP
> +/**
> + * gpu_buddy_driver_lock_held() - Assert GPU BUDDY manager lock is held
> + * @mm: Pointer to the GPU BUDDY structure.
> + *
> + * Ensure driver lock is held.
> + */
> +static inline void gpu_buddy_driver_lock_held(struct gpu_buddy *mm)
> +{
> +	if (mm->lock_dep_map)
> +		lockdep_assert(lock_is_held_type(mm->lock_dep_map, 0));
> +}
> +#else
> +static inline void gpu_buddy_driver_lock_held(struct gpu_buddy *mm)
> +{
> +}
> +#endif
> +
>   static inline u64
>   gpu_buddy_block_offset(const struct gpu_buddy_block *block)
>   {