Re: [PATCH 3/3] drm/debugfs: remove dev->debugfs_list and debugfs_mutex

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On Thu, Feb 16, 2023 at 12:33:08PM +0100, Daniel Vetter wrote:
> On Thu, Feb 09, 2023 at 09:18:38AM +0100, Christian König wrote:
> > The mutex was completely pointless in the first place since any
> > parallel adding of files to this list would result in random
> > behavior since the list is filled and consumed multiple times.
> > 
> > Completely drop that approach and just create the files directly.
> > 
> > This also re-adds the debugfs files to the render node directory and
> > removes drm_debugfs_late_register().
> > 
> > Signed-off-by: Christian König <christian.koenig@xxxxxxx>
> > ---
> >  drivers/gpu/drm/drm_debugfs.c     | 32 +++++++------------------------
> >  drivers/gpu/drm/drm_drv.c         |  3 ---
> >  drivers/gpu/drm/drm_internal.h    |  5 -----
> >  drivers/gpu/drm/drm_mode_config.c |  2 --
> >  include/drm/drm_device.h          | 15 ---------------
> >  5 files changed, 7 insertions(+), 50 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_debugfs.c b/drivers/gpu/drm/drm_debugfs.c
> > index 558e3a7271a5..a40288e67264 100644
> > --- a/drivers/gpu/drm/drm_debugfs.c
> > +++ b/drivers/gpu/drm/drm_debugfs.c
> > @@ -246,31 +246,9 @@ void drm_debugfs_dev_register(struct drm_device *dev)
> >  void drm_debugfs_minor_register(struct drm_minor *minor)
> >  {
> >  	struct drm_device *dev = minor->dev;
> > -	struct drm_debugfs_entry *entry, *tmp;
> >  
> >  	if (dev->driver->debugfs_init)
> >  		dev->driver->debugfs_init(minor);
> > -
> > -	list_for_each_entry_safe(entry, tmp, &dev->debugfs_list, list) {
> > -		debugfs_create_file(entry->file.name, 0444,
> > -				    minor->debugfs_root, entry, &drm_debugfs_entry_fops);
> > -		list_del(&entry->list);
> > -	}
> > -}
> > -
> > -void drm_debugfs_late_register(struct drm_device *dev)
> > -{
> > -	struct drm_minor *minor = dev->primary;
> > -	struct drm_debugfs_entry *entry, *tmp;
> > -
> > -	if (!minor)
> > -		return;
> > -
> > -	list_for_each_entry_safe(entry, tmp, &dev->debugfs_list, list) {
> > -		debugfs_create_file(entry->file.name, 0444,
> > -				    minor->debugfs_root, entry, &drm_debugfs_entry_fops);
> > -		list_del(&entry->list);
> > -	}
> >  }
> >  
> >  int drm_debugfs_remove_files(const struct drm_info_list *files, int count,
> > @@ -343,9 +321,13 @@ void drm_debugfs_add_file(struct drm_device *dev, const char *name,
> >  	entry->file.data = data;
> >  	entry->dev = dev;
> >  
> > -	mutex_lock(&dev->debugfs_mutex);
> > -	list_add(&entry->list, &dev->debugfs_list);
> > -	mutex_unlock(&dev->debugfs_mutex);
> > +	debugfs_create_file(name, 0444, dev->primary->debugfs_root, entry,
> > +			    &drm_debugfs_entry_fops);
> > +
> > +	/* TODO: This should probably only be a symlink */
> > +	if (dev->render)
> > +		debugfs_create_file(name, 0444, dev->render->debugfs_root,
> > +				    entry, &drm_debugfs_entry_fops);
> 
> Nope. You are fundamentally missing the point of all this, which is:
> 
> - drivers create debugfs files whenever they want to, as long as it's
>   _before_ drm_dev_register is called.
> 
> - drm_dev_register will set them all up.
> 
> This is necessary because otherwise you have the potential for some nice
> oops and stuff when userspace tries to access these files before the
> driver is ready.
> 
> Note that with sysfs all this infrastructure already exists, which is why
> you can create sysfs files whenever you feel like, and things wont go
> boom.
> 
> So yeah we need the list.
> 
> This also means that we really should not create the debugfs directories
> _before_ drm_dev_register is called. That's just fundamentally not how
> device interface setup should work:
> 
> 1. you allocate stucts and stuff
> 2. you fully init everything
> 3. you register interfaces so they become userspace visible

What I forgot to add: The mutex seems surplus and could probably be
removed. But we need the mutex once this infra is extracted to other drm
things like connector/crtc debugfs files, because you can hotplug
connectors. But maybe the mutex isn't even need in that case (since for a
single object you still should not multi-thread anything).

So removing the mutex here seems like a reasonable thing to do, but
funamentally the list and the entire delayed debugfs setup must stay.
Otherwise we cannot remove the entire debugfs_init midlayer mess without
creating huge amounts of driver bugs in the init sequencing.
-Daniel


> -Daniel
> 
> >  }
> >  EXPORT_SYMBOL(drm_debugfs_add_file);
> >  
> > diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> > index 2cbe028e548c..e7b88b65866c 100644
> > --- a/drivers/gpu/drm/drm_drv.c
> > +++ b/drivers/gpu/drm/drm_drv.c
> > @@ -597,7 +597,6 @@ static void drm_dev_init_release(struct drm_device *dev, void *res)
> >  	mutex_destroy(&dev->clientlist_mutex);
> >  	mutex_destroy(&dev->filelist_mutex);
> >  	mutex_destroy(&dev->struct_mutex);
> > -	mutex_destroy(&dev->debugfs_mutex);
> >  	drm_legacy_destroy_members(dev);
> >  }
> >  
> > @@ -638,14 +637,12 @@ static int drm_dev_init(struct drm_device *dev,
> >  	INIT_LIST_HEAD(&dev->filelist_internal);
> >  	INIT_LIST_HEAD(&dev->clientlist);
> >  	INIT_LIST_HEAD(&dev->vblank_event_list);
> > -	INIT_LIST_HEAD(&dev->debugfs_list);
> >  
> >  	spin_lock_init(&dev->event_lock);
> >  	mutex_init(&dev->struct_mutex);
> >  	mutex_init(&dev->filelist_mutex);
> >  	mutex_init(&dev->clientlist_mutex);
> >  	mutex_init(&dev->master_mutex);
> > -	mutex_init(&dev->debugfs_mutex);
> >  
> >  	ret = drmm_add_action_or_reset(dev, drm_dev_init_release, NULL);
> >  	if (ret)
> > diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h
> > index 5ff7bf88f162..e215d00ba65c 100644
> > --- a/drivers/gpu/drm/drm_internal.h
> > +++ b/drivers/gpu/drm/drm_internal.h
> > @@ -188,7 +188,6 @@ int drm_debugfs_init(struct drm_minor *minor, int minor_id,
> >  void drm_debugfs_dev_register(struct drm_device *dev);
> >  void drm_debugfs_minor_register(struct drm_minor *minor);
> >  void drm_debugfs_cleanup(struct drm_minor *minor);
> > -void drm_debugfs_late_register(struct drm_device *dev);
> >  void drm_debugfs_connector_add(struct drm_connector *connector);
> >  void drm_debugfs_connector_remove(struct drm_connector *connector);
> >  void drm_debugfs_crtc_add(struct drm_crtc *crtc);
> > @@ -205,10 +204,6 @@ static inline void drm_debugfs_cleanup(struct drm_minor *minor)
> >  {
> >  }
> >  
> > -static inline void drm_debugfs_late_register(struct drm_device *dev)
> > -{
> > -}
> > -
> >  static inline void drm_debugfs_connector_add(struct drm_connector *connector)
> >  {
> >  }
> > diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> > index 87eb591fe9b5..8525ef851540 100644
> > --- a/drivers/gpu/drm/drm_mode_config.c
> > +++ b/drivers/gpu/drm/drm_mode_config.c
> > @@ -54,8 +54,6 @@ int drm_modeset_register_all(struct drm_device *dev)
> >  	if (ret)
> >  		goto err_connector;
> >  
> > -	drm_debugfs_late_register(dev);
> > -
> >  	return 0;
> >  
> >  err_connector:
> > diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h
> > index 7cf4afae2e79..900ad7478dd8 100644
> > --- a/include/drm/drm_device.h
> > +++ b/include/drm/drm_device.h
> > @@ -311,21 +311,6 @@ struct drm_device {
> >  	 */
> >  	struct drm_fb_helper *fb_helper;
> >  
> > -	/**
> > -	 * @debugfs_mutex:
> > -	 *
> > -	 * Protects &debugfs_list access.
> > -	 */
> > -	struct mutex debugfs_mutex;
> > -
> > -	/**
> > -	 * @debugfs_list:
> > -	 *
> > -	 * List of debugfs files to be created by the DRM device. The files
> > -	 * must be added during drm_dev_register().
> > -	 */
> > -	struct list_head debugfs_list;
> > -
> >  	/* Everything below here is for legacy driver, never use! */
> >  	/* private: */
> >  #if IS_ENABLED(CONFIG_DRM_LEGACY)
> > -- 
> > 2.34.1
> > 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

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



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