Re: [PATCH 3/4] drm/panthor: show device-wide list of DRM GEM objects over DebugFS

[Boris Brezillon <boris.brezillon@collabora.com>]

On Sun, 16 Mar 2025 21:51:34 +0000
Adrián Larumbe <adrian.larumbe@collabora.com> wrote:

> Add a device DebugFS file that displays a complete list of all the DRM GEM
> objects that are exposed to UM through a DRM handle.
> 
> Since leaking object identifiers that might belong to a different NS is
> inadmissible, this functionality is only made available in debug builds
> with DEBUGFS support enabled.
> 
> File format is that of a table, with each entry displaying a variety of
> fields with information about each GEM object.
> 
> Each GEM object entry in the file displays the following information
> fields: Client PID, BO's global name, reference count, BO virtual size, BO
> resize size, VM address in its DRM-managed range, BO label and a flag
> bitmask.
> 
> Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> ---
>  drivers/gpu/drm/panthor/panthor_device.c |   5 ++
>  drivers/gpu/drm/panthor/panthor_device.h |   8 ++
>  drivers/gpu/drm/panthor/panthor_drv.c    |  26 ++++++
>  drivers/gpu/drm/panthor/panthor_gem.c    | 101 +++++++++++++++++++++++
>  drivers/gpu/drm/panthor/panthor_gem.h    |  22 +++++
>  5 files changed, 162 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_device.c b/drivers/gpu/drm/panthor/panthor_device.c
> index a9da1d1eeb70..7df12eefc39f 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.c
> +++ b/drivers/gpu/drm/panthor/panthor_device.c
> @@ -263,6 +263,11 @@ int panthor_device_init(struct panthor_device *ptdev)
>  	pm_runtime_set_autosuspend_delay(ptdev->base.dev, 50);
>  	pm_runtime_use_autosuspend(ptdev->base.dev);
>  
> +#ifdef CONFIG_DEBUG_FS
> +	drmm_mutex_init(&ptdev->base, &ptdev->gems_lock);
> +	INIT_LIST_HEAD(&ptdev->gems);
> +#endif
> +
>  	ret = drm_dev_register(&ptdev->base, 0);
>  	if (ret)
>  		goto err_disable_autosuspend;
> diff --git a/drivers/gpu/drm/panthor/panthor_device.h b/drivers/gpu/drm/panthor/panthor_device.h
> index da6574021664..6c030978cdc3 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.h
> +++ b/drivers/gpu/drm/panthor/panthor_device.h
> @@ -205,6 +205,14 @@ struct panthor_device {
>  
>  	/** @fast_rate: Maximum device clock frequency. Set by DVFS */
>  	unsigned long fast_rate;
> +
> +#ifdef CONFIG_DEBUG_FS
> +	/** @gems_lock: Protects the device-wide list of GEM objects. */
> +	struct mutex gems_lock;
> +
> +	/** @gems: Device-wide list of GEM objects owned by at least one file. */
> +	struct list_head gems;

	struct {
		struct mutex lock;
		struct list_head list;
	} gems;

> +#endif
>  };
>  
>  struct panthor_gpu_usage {
> diff --git a/drivers/gpu/drm/panthor/panthor_drv.c b/drivers/gpu/drm/panthor/panthor_drv.c
> index f41b8946258f..6663eff44bdc 100644
> --- a/drivers/gpu/drm/panthor/panthor_drv.c
> +++ b/drivers/gpu/drm/panthor/panthor_drv.c
> @@ -1525,9 +1525,35 @@ static const struct file_operations panthor_drm_driver_fops = {
>  };
>  
>  #ifdef CONFIG_DEBUG_FS
> +static int panthor_gems_show(struct seq_file *m, void *data)
> +{
> +	struct drm_info_node *node = m->private;
> +	struct drm_device *dev = node->minor->dev;
> +	struct panthor_device *ptdev = container_of(dev, struct panthor_device, base);
> +
> +	panthor_gem_print_objects(ptdev, m);
> +
> +	return 0;
> +}
> +
> +
> +static struct drm_info_list panthor_debugfs_list[] = {
> +	{"gems", panthor_gems_show, 0, NULL},
> +};
> +
> +static int panthor_gems_debugfs_init(struct drm_minor *minor)
> +{
> +	drm_debugfs_create_files(panthor_debugfs_list,
> +				 ARRAY_SIZE(panthor_debugfs_list),
> +				 minor->debugfs_root, minor);
> +
> +	return 0;
> +}
> +
>  static void panthor_debugfs_init(struct drm_minor *minor)
>  {
>  	panthor_mmu_debugfs_init(minor);
> +	panthor_gems_debugfs_init(minor);
>  }
>  #endif
>  
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
> index 3c58bb2965ea..8cea6caf3143 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.c
> +++ b/drivers/gpu/drm/panthor/panthor_gem.c
> @@ -17,6 +17,16 @@ static void panthor_gem_free_object(struct drm_gem_object *obj)
>  {
>  	struct panthor_gem_object *bo = to_panthor_bo(obj);
>  	struct drm_gem_object *vm_root_gem = bo->exclusive_vm_root_gem;
> +#ifdef CONFIG_DEBUG_FS
> +	struct drm_device *dev = bo->base.base.dev;
> +	struct panthor_device *ptdev = container_of(dev, struct panthor_device, base);
> +
> +	if (!list_empty(&bo->gems_node)) {
> +		mutex_lock(&ptdev->gems_lock);
> +		list_del_init(&bo->gems_node);
> +		mutex_unlock(&ptdev->gems_lock);
> +	}
> +#endif

Can we add helpers to add/remove a GEM to the list and define dummy
implementations for the !CONFIG_DEBUG_FS case?

#ifdef CONFIG_DEBUG_FS
static void panthor_gem_debugfs_bo_init(struct panthor_gem_object *bo)
{
	INIT_LIST_HEAD(&obj->gems_node);
	obj->creator.tgid = current->group_leader->pid;
	get_task_comm(obj->creator.process_name, current->group_leader);
}

static void panthor_gem_debugfs_bo_add(struct panthor_gem_object *bo)
{
	struct panthor_device *ptdev = container_of(bo->base.base.dev,
						    struct panthor_device, base);

	mutex_lock(&ptdev->gems_lock);
	list_add_tail(&bo->gems_node, &ptdev->gems);
	mutex_unlock(&ptdev->gems_lock);
}

static void panthor_gem_debugfs_bo_rm(struct panthor_gem_object *bo)
{
	struct panthor_device *ptdev = container_of(bo->base.base.dev,
						    struct panthor_device, base);
	
	if (list_empty(&bo->gems_node))
		return;

	mutex_lock(&ptdev->gems_lock);
	list_del_init(&bo->gems_node);
	mutex_unlock(&ptdev->gems_lock);
}
#else
static void panthor_gem_debugfs_bo_init(struct panthor_gem_object *bo) {}
static void panthor_gem_debugfs_bo_add(struct panthor_gem_object *bo) {}
static void panthor_gem_debugfs_bo_rm(struct panthor_gem_object *bo) {}
#endif

>  
>  	kfree(bo->label);
>  	mutex_destroy(&bo->label_lock);
> @@ -201,6 +211,12 @@ struct drm_gem_object *panthor_gem_create_object(struct drm_device *ddev, size_t
>  	drm_gem_gpuva_set_lock(&obj->base.base, &obj->gpuva_list_lock);
>  	mutex_init(&obj->label_lock);
>  
> +#ifdef CONFIG_DEBUG_FS
> +	INIT_LIST_HEAD(&obj->gems_node);
> +	obj->creator.tgid = current->group_leader->pid;
> +	get_task_comm(obj->creator.process_name, current->group_leader);
> +#endif

	panthor_gem_debugfs_bo_init(obj);
	
> +
>  	return &obj->base.base;
>  }
>  
> @@ -224,6 +240,10 @@ panthor_gem_create_with_handle(struct drm_file *file,
>  	int ret;
>  	struct drm_gem_shmem_object *shmem;
>  	struct panthor_gem_object *bo;
> +#ifdef CONFIG_DEBUG_FS
> +	struct panthor_device *ptdev =
> +		container_of(ddev, struct panthor_device, base);
> +#endif
>  
>  	shmem = drm_gem_shmem_create(ddev, *size);
>  	if (IS_ERR(shmem))
> @@ -249,6 +269,12 @@ panthor_gem_create_with_handle(struct drm_file *file,
>  	/* drop reference from allocate - handle holds it now. */
>  	drm_gem_object_put(&shmem->base);
>  
> +#ifdef CONFIG_DEBUG_FS
> +	mutex_lock(&ptdev->gems_lock);
> +	list_add_tail(&bo->gems_node, &ptdev->gems);
> +	mutex_unlock(&ptdev->gems_lock);
> +#endif

	panthor_gem_debugfs_bo_rm(bo);

> +
>  	return ret;
>  }
>  
> @@ -265,3 +291,78 @@ panthor_gem_label_bo(struct drm_gem_object *obj, const char *label)
>  
>  	kfree(old_label);
>  }
> +
> +#ifdef CONFIG_DEBUG_FS
> +static bool panfrost_gem_print_flag(const char *name,
> +				    bool is_set,
> +				    bool other_flags_printed,
> +				    struct seq_file *m)
> +{
> +	if (is_set)
> +		seq_printf(m, "%s%s", other_flags_printed ? "," : "", name);
> +
> +	return is_set | other_flags_printed;
> +}
> +
> +void panthor_gem_print_objects(struct panthor_device *ptdev,
> +				struct seq_file *m)
> +{
> +	size_t total = 0, total_resident = 0, total_reclaimable = 0;
> +	struct panthor_gem_object *bo;
> +
> +	seq_puts(m, "created-by                      global-name     refcount        size            resident-size   file-offset     flags           label\n");
> +	seq_puts(m, "------------------------------------------------------------------------------------------------------------------------------------------------\n");
> +
> +	mutex_lock(&ptdev->gems_lock);
> +	list_for_each_entry(bo, &ptdev->gems, gems_node) {
> +		unsigned int refcount = kref_read(&bo->base.base.refcount);
> +		char creator_info[32] = {};
> +		bool has_flags = false;
> +		size_t resident_size;
> +
> +		/* Skip BOs being destroyed. */
> +		if (!refcount)
> +			continue;
> +
> +		resident_size = bo->base.pages != NULL ? bo->base.base.size : 0;
> +
> +		snprintf(creator_info, sizeof(creator_info),
> +			 "%s/%d", bo->creator.process_name, bo->creator.tgid);
> +		seq_printf(m, "%-32s%-16d%-16d%-16zd%-16zd%-16lx",
> +			   creator_info,
> +			   bo->base.base.name,
> +			   refcount,
> +			   bo->base.base.size,
> +			   resident_size,
> +			   drm_vma_node_start(&bo->base.base.vma_node));
> +
> +		seq_puts(m, "(");
> +		has_flags = panfrost_gem_print_flag("imported", bo->base.base.import_attach != NULL,
> +						    has_flags, m);
> +		has_flags = panfrost_gem_print_flag("exported", bo->base.base.dma_buf != NULL,
> +						    has_flags, m);
> +		if (bo->base.madv < 0)
> +			has_flags = panfrost_gem_print_flag("purged", true, has_flags, m);
> +		else if (bo->base.madv > 0)
> +			has_flags = panfrost_gem_print_flag("purgeable", true, has_flags, m);
> +		if (!has_flags)
> +			seq_puts(m, "none");
> +		seq_puts(m, ")");
> +
> +		mutex_lock(&bo->label_lock);
> +		seq_printf(m, "%-16s%-60s", "", bo->label ? : NULL);
> +		mutex_unlock(&bo->label_lock);
> +		seq_puts(m, "\n");

Let's have a panthor_gem_debugfs_bo_print() helper to print a single BO.

> +
> +		total += bo->base.base.size;
> +		total_resident += resident_size;
> +		if (bo->base.madv > 0)
> +			total_reclaimable += resident_size;
> +	}
> +	mutex_unlock(&ptdev->gems_lock);
> +
> +	seq_puts(m, "================================================================================================================================================\n");
> +	seq_printf(m, "Total size: %zd, Total resident: %zd, Total reclaimable: %zd\n",
> +		   total, total_resident, total_reclaimable);
> +}
> +#endif
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.h b/drivers/gpu/drm/panthor/panthor_gem.h
> index da9268d24566..c0be30434b34 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.h
> +++ b/drivers/gpu/drm/panthor/panthor_gem.h
> @@ -55,6 +55,23 @@ struct panthor_gem_object {
>  
>  	/** @label_lock: Lock that protects access to the @label field. */
>  	struct mutex label_lock;
> +
> +#ifdef CONFIG_DEBUG_FS
> +	/**
> +	 * @gems_node: Node used to insert the object in the device-wide list of
> +	 * GEM objects, to display information about it through a DebugFS file.
> +	 */
> +	struct list_head gems_node;
> +
> +	/** @creator: Information about the UM process which created the GEM. */
> +	struct {
> +		/** @process_name: Group leader name in owning thread's process */
> +		char process_name[TASK_COMM_LEN];
> +
> +		/** @tgid: PID of the thread's group leader within its process */
> +		pid_t tgid;
> +	} creator;

Can we put all these fields under a debugfs struct?

struct panthor_gem_debugfs {
	/**
	 * @gems_node: Node used to insert the object in the device-wide list of
	 * GEM objects, to display information about it through a DebugFS file.
	 */
	struct list_head gems_node;

	/** @creator: Information about the UM process which created the GEM. */
	struct {
		/** @process_name: Group leader name in owning thread's process */
		char process_name[TASK_COMM_LEN];
	
		/** @tgid: PID of the thread's group leader within its process */
		pid_t tgid;
	} creator;
};

...

struct panthor_gem_object {
	...

#ifdef CONFIG_DEBUG_FS
	struct panthor_gem_debugfs debugfs;
#endif

	...
};

> +#endif
>  };
>  
>  /**
> @@ -150,4 +167,9 @@ panthor_kernel_bo_create(struct panthor_device *ptdev, struct panthor_vm *vm,
>  
>  void panthor_kernel_bo_destroy(struct panthor_kernel_bo *bo);
>  
> +#ifdef CONFIG_DEBUG_FS
> +void panthor_gem_print_objects(struct panthor_device *pfdev,
> +			       struct seq_file *m);

s/panthor_gem_print_objects/panthor_gem_debugfs_print_bos/

> +#endif
> +
>  #endif /* __PANTHOR_GEM_H__ */