Re: [Intel-gfx] [PATCH 5/6] drm/ttm: Initialize debugfs from ttm_global_init()

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Jul 19, 2021 at 01:30:46PM -0500, Jason Ekstrand wrote:
> We create a bunch of debugfs entries as a side-effect of
> ttm_global_init() and then never clean them up.  This isn't usually a
> problem because we free the whole debugfs directory on module unload.
> However, if the global reference count ever goes to zero and then
> ttm_global_init() is called again, we'll re-create those debugfs entries
> and debugfs will complain in dmesg that we're creating entries that
> already exist.  This patch fixes this problem by changing the lifetime
> of the whole TTM debugfs directory to match that of the TTM global
> state.
> 
> Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
> ---
>  drivers/gpu/drm/ttm/ttm_device.c | 12 ++++++++++++
>  drivers/gpu/drm/ttm/ttm_module.c |  4 ----
>  2 files changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ttm/ttm_device.c b/drivers/gpu/drm/ttm/ttm_device.c
> index 519deea8e39b7..74e3b460132b3 100644
> --- a/drivers/gpu/drm/ttm/ttm_device.c
> +++ b/drivers/gpu/drm/ttm/ttm_device.c
> @@ -44,6 +44,8 @@ static unsigned ttm_glob_use_count;
>  struct ttm_global ttm_glob;
>  EXPORT_SYMBOL(ttm_glob);
>  
> +struct dentry *ttm_debugfs_root;
> +
>  static void ttm_global_release(void)
>  {
>  	struct ttm_global *glob = &ttm_glob;
> @@ -53,6 +55,7 @@ static void ttm_global_release(void)
>  		goto out;
>  
>  	ttm_pool_mgr_fini();
> +	debugfs_remove(ttm_debugfs_root);
>  
>  	__free_page(glob->dummy_read_page);
>  	memset(glob, 0, sizeof(*glob));
> @@ -73,6 +76,13 @@ static int ttm_global_init(void)
>  
>  	si_meminfo(&si);
>  
> +	ttm_debugfs_root = debugfs_create_dir("ttm", NULL);
> +	if (IS_ERR(ttm_debugfs_root)) {
> +		ret = PTR_ERR(ttm_debugfs_root);
> +		ttm_debugfs_root = NULL;
> +		goto out;
> +	}
> +
>  	/* Limit the number of pages in the pool to about 50% of the total
>  	 * system memory.
>  	 */
> @@ -100,6 +110,8 @@ static int ttm_global_init(void)
>  	debugfs_create_atomic_t("buffer_objects", 0444, ttm_debugfs_root,
>  				&glob->bo_count);
>  out:
> +	if (ret && ttm_debugfs_root)
> +		debugfs_remove(ttm_debugfs_root);
>  	if (ret)
>  		--ttm_glob_use_count;
>  	mutex_unlock(&ttm_global_mutex);
> diff --git a/drivers/gpu/drm/ttm/ttm_module.c b/drivers/gpu/drm/ttm/ttm_module.c
> index 997c458f68a9a..88554f2db11fe 100644
> --- a/drivers/gpu/drm/ttm/ttm_module.c
> +++ b/drivers/gpu/drm/ttm/ttm_module.c
> @@ -72,17 +72,13 @@ pgprot_t ttm_prot_from_caching(enum ttm_caching caching, pgprot_t tmp)
>  	return tmp;
>  }
>  
> -struct dentry *ttm_debugfs_root;
> -
>  static int __init ttm_init(void)
>  {
> -	ttm_debugfs_root = debugfs_create_dir("ttm", NULL);
>  	return 0;
>  }
>  
>  static void __exit ttm_exit(void)
>  {
> -	debugfs_remove(ttm_debugfs_root);
>  }

I think you can delete these functions and the lines below too, they
should be optional. With that:

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

-Daniel

>  
>  module_init(ttm_init);
> -- 
> 2.31.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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