Re: [Intel-gfx] [PATCH 22/51] drm: manage drm_minor cleanup with drmm_

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Mar 11, 2020 at 10:59:10AM +0100, Thomas Zimmermann wrote:
> Hi
> 
> Am 02.03.20 um 23:26 schrieb Daniel Vetter:
> > The cleanup here is somewhat tricky, since we can't tell apart the
> > allocated minor index from 0. So register a cleanup action first, and
> > if the index allocation fails, unregister that cleanup action again to
> > avoid bad mistakes.
> > 
> > The kdev for the minor already handles NULL, so no problem there.
> > 
> > Hence add drmm_remove_action() to the drm_managed library.
> > 
> > v2: Make pointer math around void ** consistent with what Laurent
> > suggested.
> > 
> > Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > ---
> >  drivers/gpu/drm/drm_drv.c     | 74 +++++++++++++----------------------
> >  drivers/gpu/drm/drm_managed.c | 28 +++++++++++++
> >  include/drm/drm_managed.h     |  4 ++
> >  3 files changed, 59 insertions(+), 47 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> > index 23e5b0e7e041..29d106195ab3 100644
> > --- a/drivers/gpu/drm/drm_drv.c
> > +++ b/drivers/gpu/drm/drm_drv.c
> > @@ -93,19 +93,35 @@ static struct drm_minor **drm_minor_get_slot(struct drm_device *dev,
> >  	}
> >  }
> >  
> > +static void drm_minor_alloc_release(struct drm_device *dev, void *data)
> > +{
> > +	struct drm_minor *minor = data;
> > +	unsigned long flags;
> > +
> > +	put_device(minor->kdev);
> > +
> > +	spin_lock_irqsave(&drm_minor_lock, flags);
> > +	idr_remove(&drm_minors_idr, minor->index);
> > +	spin_unlock_irqrestore(&drm_minor_lock, flags);
> > +}
> > +
> >  static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
> >  {
> >  	struct drm_minor *minor;
> >  	unsigned long flags;
> >  	int r;
> >  
> > -	minor = kzalloc(sizeof(*minor), GFP_KERNEL);
> > +	minor = drmm_kzalloc(dev, sizeof(*minor), GFP_KERNEL);
> >  	if (!minor)
> >  		return -ENOMEM;
> >  
> >  	minor->type = type;
> >  	minor->dev = dev;
> >  
> > +	r = drmm_add_action(dev, drm_minor_alloc_release, minor);
> > +	if (r)
> > +		return r;
> > +
> >  	idr_preload(GFP_KERNEL);
> >  	spin_lock_irqsave(&drm_minor_lock, flags);
> >  	r = idr_alloc(&drm_minors_idr,
> > @@ -116,47 +132,18 @@ static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
> >  	spin_unlock_irqrestore(&drm_minor_lock, flags);
> >  	idr_preload_end();
> >  
> > -	if (r < 0)
> > -		goto err_free;
> > +	if (r < 0) {
> > +		drmm_remove_action(dev, drm_minor_alloc_release, minor);
> > +		return r;
> > +	}
> >  
> >  	minor->index = r;
> > -
> >  	minor->kdev = drm_sysfs_minor_alloc(minor);
> > -	if (IS_ERR(minor->kdev)) {
> > -		r = PTR_ERR(minor->kdev);
> > -		goto err_index;
> > -	}
> > +	if (IS_ERR(minor->kdev))
> > +		return PTR_ERR(minor->kdev);
> >  
> >  	*drm_minor_get_slot(dev, type) = minor;
> >  	return 0;
> > -
> > -err_index:
> > -	spin_lock_irqsave(&drm_minor_lock, flags);
> > -	idr_remove(&drm_minors_idr, minor->index);
> > -	spin_unlock_irqrestore(&drm_minor_lock, flags);
> > -err_free:
> > -	kfree(minor);
> > -	return r;
> > -}
> 
> TBH, I think you're reducing code quality by removing the rollback code
> from init functions, just for the sake of it.
> 
> Specifically in this case here, you saved a few lines of code, but the
> overall flow is way more complicated to follow. That's typically a
> reliably source of bugs. This call to drmm_remove_action() just makes it
> worse.
> 
> Rather, see my remark on OOP destruction in patch 21. For now, I'd focus
> on the device cleanup and leave init functions as they are.

Ah, I can simplify this with add_action_or_reset. This removes the only
user of drmm_remove_action, which I think is actually a good thing :-)
-Daniel

> 
> Best regards
> Thomas
> 
> > -
> > -static void drm_minor_free(struct drm_device *dev, unsigned int type)
> > -{
> > -	struct drm_minor **slot, *minor;
> > -	unsigned long flags;
> > -
> > -	slot = drm_minor_get_slot(dev, type);
> > -	minor = *slot;
> > -	if (!minor)
> > -		return;
> > -
> > -	put_device(minor->kdev);
> > -
> > -	spin_lock_irqsave(&drm_minor_lock, flags);
> > -	idr_remove(&drm_minors_idr, minor->index);
> > -	spin_unlock_irqrestore(&drm_minor_lock, flags);
> > -
> > -	kfree(minor);
> > -	*slot = NULL;
> >  }
> >  
> >  static int drm_minor_register(struct drm_device *dev, unsigned int type)
> > @@ -678,16 +665,16 @@ int drm_dev_init(struct drm_device *dev,
> >  	if (drm_core_check_feature(dev, DRIVER_RENDER)) {
> >  		ret = drm_minor_alloc(dev, DRM_MINOR_RENDER);
> >  		if (ret)
> > -			goto err_minors;
> > +			goto err;
> >  	}
> >  
> >  	ret = drm_minor_alloc(dev, DRM_MINOR_PRIMARY);
> >  	if (ret)
> > -		goto err_minors;
> > +		goto err;
> >  
> >  	ret = drm_legacy_create_map_hash(dev);
> >  	if (ret)
> > -		goto err_minors;
> > +		goto err;
> >  
> >  	drm_legacy_ctxbitmap_init(dev);
> >  
> > @@ -695,7 +682,7 @@ int drm_dev_init(struct drm_device *dev,
> >  		ret = drm_gem_init(dev);
> >  		if (ret) {
> >  			DRM_ERROR("Cannot initialize graphics execution manager (GEM)\n");
> > -			goto err_ctxbitmap;
> > +			goto err;
> >  		}
> >  	}
> >  
> > @@ -708,10 +695,6 @@ int drm_dev_init(struct drm_device *dev,
> >  err_setunique:
> >  	if (drm_core_check_feature(dev, DRIVER_GEM))
> >  		drm_gem_destroy(dev);
> > -err_ctxbitmap:
> > -err_minors:
> > -	drm_minor_free(dev, DRM_MINOR_PRIMARY);
> > -	drm_minor_free(dev, DRM_MINOR_RENDER);
> >  err:
> >  	drm_managed_release(dev);
> >  
> > @@ -776,9 +759,6 @@ void drm_dev_fini(struct drm_device *dev)
> >  
> >  	if (drm_core_check_feature(dev, DRIVER_GEM))
> >  		drm_gem_destroy(dev);
> > -
> > -	drm_minor_free(dev, DRM_MINOR_PRIMARY);
> > -	drm_minor_free(dev, DRM_MINOR_RENDER);
> >  }
> >  EXPORT_SYMBOL(drm_dev_fini);
> >  
> > diff --git a/drivers/gpu/drm/drm_managed.c b/drivers/gpu/drm/drm_managed.c
> > index 514d5bd42446..0883615c2088 100644
> > --- a/drivers/gpu/drm/drm_managed.c
> > +++ b/drivers/gpu/drm/drm_managed.c
> > @@ -142,6 +142,34 @@ int __drmm_add_action(struct drm_device *dev,
> >  }
> >  EXPORT_SYMBOL(__drmm_add_action);
> >  
> > +void drmm_remove_action(struct drm_device *dev,
> > +			drmres_release_t action,
> > +			void *data)
> > +{
> > +	struct drmres *dr = NULL, *tmp;
> > +	unsigned long flags;
> > +
> > +	if (!data)
> > +		return;
> > +
> > +	spin_lock_irqsave(&dev->managed.lock, flags);
> > +	list_for_each_entry(tmp, &dev->managed.resources, node.entry) {
> > +		if (tmp->node.release == action &&
> > +		    *(void **)&tmp->data == data) {
> > +			dr = tmp;
> > +			del_dr(dev, dr);
> > +			break;
> > +		}
> > +	}
> > +	spin_unlock_irqrestore(&dev->managed.lock, flags);
> > +
> > +	if (WARN_ON(!dr))
> > +		return;
> > +
> > +	kfree(dr);
> > +}
> > +EXPORT_SYMBOL(drmm_remove_action);
> > +
> >  void *drmm_kmalloc(struct drm_device *dev, size_t size, gfp_t gfp)
> >  {
> >  	struct drmres *dr;
> > diff --git a/include/drm/drm_managed.h b/include/drm/drm_managed.h
> > index 89e6fce9f689..5280209dff92 100644
> > --- a/include/drm/drm_managed.h
> > +++ b/include/drm/drm_managed.h
> > @@ -17,6 +17,10 @@ int __must_check __drmm_add_action(struct drm_device *dev,
> >  				   drmres_release_t action,
> >  				   void *data, const char *name);
> >  
> > +void drmm_remove_action(struct drm_device *dev,
> > +			drmres_release_t action,
> > +			void *data);
> > +
> >  void drmm_add_final_kfree(struct drm_device *dev, void *parent);
> >  
> >  void *drmm_kmalloc(struct drm_device *dev, size_t size, gfp_t gfp) __malloc;
> > 
> 
> -- 
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Felix Imendörffer
> 




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