Re: [PATCH] drm/prime: keep a reference from the handle to exported dma-buf (v4)

[Imre Deak <imre.deak@intel.com>]

On Wed, 2013-04-17 at 10:21 +0200, Daniel Vetter wrote:
> On Wed, Apr 17, 2013 at 02:38:02PM +1000, Dave Airlie wrote:
> > Currently we have a problem with this:
> > 1. i915: create gem object
> > 2. i915: export gem object to prime
> > 3. radeon: import gem object
> > 4. close prime fd
> > 5. radeon: unref object
> > 6. i915: unref object
> > 
> > i915 has an imported object reference in its file priv, that isn't
> > cleaned up properly until fd close. The reference gets added at step 2,
> > but at step 6 we don't have enough info to clean it up.
> > 
> > The solution is to take a reference on the dma-buf when we export it,
> > and drop the reference when the gem handle goes away.
> > 
> > So when we export a dma_buf from a gem object, we keep track of it
> > with the handle, we take a reference to the dma_buf. When we close
> > the handle (i.e. userspace is finished with the buffer), we drop
> > the reference to the dma_buf, and it gets collected.
> > 
> > This patch isn't meant to fix any other problem or bikesheds, and it doesn't
> > fix any races with other scenarios.
> > 
> > v1.1: move export symbol line back up.
> > 
> > v2: okay I had to do a bit more, as the first patch showed a leak
> > on one of my tests, that I found using the dma-buf debugfs support,
> > the problem case is exporting a buffer twice with the same handle,
> > we'd add another export handle for it unnecessarily, however
> > we now fail if we try to export the same object with a different gem handle,
> > however I'm not sure if that is a case I want to support, and I've
> > gotten the code to WARN_ON if we hit something like that.
> > 
> > v2.1: rebase this patch, write better commit msg.
> > v3: cleanup error handling, track import vs export in linked list,
> > these two patches were separate previously, but seem to work better
> > like this.
> > v4: danvet is correct, this code is no longer useful, since the buffer
> > better exist, so remove it.
> > 
> > Signed-off-by: Dave Airlie <airlied@redhat.com>
> 
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
> On bikeshed review level I wonder whether we shouldn't just grab a
> reference unconditonally when inserting it into the handle_to_fd lookup
> lists. But I need to think through a few other cases and apparently the
> self-import test is still a bit broken. So this is material for follow-up
> patches.

Yes, this is needed, otherwise closing the prime fd will leave stale
pointers to the dma buf in the importer's lookup table. I've sent an
update to igt/prime_self_test to intel-gfx for showing this.

--Imre

> -Daniel
> 
> > ---
> >  drivers/gpu/drm/drm_gem.c   |  4 +-
> >  drivers/gpu/drm/drm_prime.c | 95 +++++++++++++++++++++++++++++----------------
> >  include/drm/drmP.h          |  4 +-
> >  3 files changed, 65 insertions(+), 38 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> > index af779ae..cf919e3 100644
> > --- a/drivers/gpu/drm/drm_gem.c
> > +++ b/drivers/gpu/drm/drm_gem.c
> > @@ -205,11 +205,11 @@ static void
> >  drm_gem_remove_prime_handles(struct drm_gem_object *obj, struct drm_file *filp)
> >  {
> >  	if (obj->import_attach) {
> > -		drm_prime_remove_imported_buf_handle(&filp->prime,
> > +		drm_prime_remove_buf_handle(&filp->prime,
> >  				obj->import_attach->dmabuf);
> >  	}
> >  	if (obj->export_dma_buf) {
> > -		drm_prime_remove_imported_buf_handle(&filp->prime,
> > +		drm_prime_remove_buf_handle(&filp->prime,
> >  				obj->export_dma_buf);
> >  	}
> >  }
> > diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> > index 366910d..b4ed808 100644
> > --- a/drivers/gpu/drm/drm_prime.c
> > +++ b/drivers/gpu/drm/drm_prime.c
> > @@ -57,10 +57,14 @@
> >   * use the drm_gem_prime_{import,export} helpers.
> >   */
> >  
> > +#define PRIME_IMPORT 1
> > +#define PRIME_EXPORT 2
> > +
> >  struct drm_prime_member {
> >  	struct list_head entry;
> >  	struct dma_buf *dma_buf;
> >  	uint32_t handle;
> > +	int type;
> >  };
> >  
> >  static struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach,
> > @@ -157,6 +161,8 @@ static const struct dma_buf_ops drm_gem_prime_dmabuf_ops =  {
> >  	.vunmap = drm_gem_dmabuf_vunmap,
> >  };
> >  
> > +static int drm_prime_add_exported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t handle);
> > +
> >  /**
> >   * DOC: PRIME Helpers
> >   *
> > @@ -200,7 +206,9 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev,
> >  {
> >  	struct drm_gem_object *obj;
> >  	void *buf;
> > -	int ret;
> > +	int ret = 0;
> > +	struct dma_buf *dmabuf;
> > +	uint32_t exp_handle;
> >  
> >  	obj = drm_gem_object_lookup(dev, file_priv, handle);
> >  	if (!obj)
> > @@ -209,43 +217,44 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev,
> >  	mutex_lock(&file_priv->prime.lock);
> >  	/* re-export the original imported object */
> >  	if (obj->import_attach) {
> > -		get_dma_buf(obj->import_attach->dmabuf);
> > -		*prime_fd = dma_buf_fd(obj->import_attach->dmabuf, flags);
> > -		drm_gem_object_unreference_unlocked(obj);
> > -		mutex_unlock(&file_priv->prime.lock);
> > -		return 0;
> > +		dmabuf = obj->import_attach->dmabuf;
> > +		goto out_have_obj;
> >  	}
> >  
> >  	if (obj->export_dma_buf) {
> > -		get_dma_buf(obj->export_dma_buf);
> > -		*prime_fd = dma_buf_fd(obj->export_dma_buf, flags);
> > -		drm_gem_object_unreference_unlocked(obj);
> > -	} else {
> > -		buf = dev->driver->gem_prime_export(dev, obj, flags);
> > -		if (IS_ERR(buf)) {
> > -			/* normally the created dma-buf takes ownership of the ref,
> > -			 * but if that fails then drop the ref
> > -			 */
> > -			drm_gem_object_unreference_unlocked(obj);
> > -			mutex_unlock(&file_priv->prime.lock);
> > -			return PTR_ERR(buf);
> > -		}
> > -		obj->export_dma_buf = buf;
> > -		*prime_fd = dma_buf_fd(buf, flags);
> > +		dmabuf = obj->export_dma_buf;
> > +		goto out_have_obj;
> > +	}
> > +
> > +	buf = dev->driver->gem_prime_export(dev, obj, flags);
> > +	if (IS_ERR(buf)) {
> > +		/* normally the created dma-buf takes ownership of the ref,
> > +		 * but if that fails then drop the ref
> > +		 */
> > +		ret = PTR_ERR(buf);
> > +		goto out;
> >  	}
> > +	obj->export_dma_buf = buf;
> > +
> >  	/* if we've exported this buffer the cheat and add it to the import list
> >  	 * so we get the correct handle back
> >  	 */
> > -	ret = drm_prime_add_imported_buf_handle(&file_priv->prime,
> > -			obj->export_dma_buf, handle);
> > -	if (ret) {
> > -		drm_gem_object_unreference_unlocked(obj);
> > -		mutex_unlock(&file_priv->prime.lock);
> > -		return ret;
> > -	}
> > +	ret = drm_prime_add_exported_buf_handle(&file_priv->prime,
> > +						obj->export_dma_buf, handle);
> > +	if (ret)
> > +		goto out;
> >  
> > +	*prime_fd = dma_buf_fd(buf, flags);
> >  	mutex_unlock(&file_priv->prime.lock);
> >  	return 0;
> > +
> > +out_have_obj:
> > +	get_dma_buf(dmabuf);
> > +	*prime_fd = dma_buf_fd(dmabuf, flags);
> > +out:
> > +	drm_gem_object_unreference_unlocked(obj);
> > +	mutex_unlock(&file_priv->prime.lock);
> > +	return ret;
> >  }
> >  EXPORT_SYMBOL(drm_gem_prime_handle_to_fd);
> >  
> > @@ -314,7 +323,7 @@ int drm_gem_prime_fd_to_handle(struct drm_device *dev,
> >  
> >  	mutex_lock(&file_priv->prime.lock);
> >  
> > -	ret = drm_prime_lookup_imported_buf_handle(&file_priv->prime,
> > +	ret = drm_prime_lookup_buf_handle(&file_priv->prime,
> >  			dma_buf, handle);
> >  	if (!ret) {
> >  		ret = 0;
> > @@ -491,7 +500,7 @@ void drm_prime_destroy_file_private(struct drm_prime_file_private *prime_fpriv)
> >  }
> >  EXPORT_SYMBOL(drm_prime_destroy_file_private);
> >  
> > -int drm_prime_add_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t handle)
> > +static int drm_prime_add_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t handle, int type)
> >  {
> >  	struct drm_prime_member *member;
> >  
> > @@ -501,12 +510,25 @@ int drm_prime_add_imported_buf_handle(struct drm_prime_file_private *prime_fpriv
> >  
> >  	member->dma_buf = dma_buf;
> >  	member->handle = handle;
> > +	member->type = type;
> >  	list_add(&member->entry, &prime_fpriv->head);
> >  	return 0;
> >  }
> > +
> > +int drm_prime_add_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t handle)
> > +{
> > +	return drm_prime_add_buf_handle(prime_fpriv, dma_buf, handle, PRIME_IMPORT);
> > +}
> >  EXPORT_SYMBOL(drm_prime_add_imported_buf_handle);
> >  
> > -int drm_prime_lookup_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t *handle)
> > +static int drm_prime_add_exported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t handle)
> > +{
> > +	/* take a reference to the buf handle for this case */
> > +	get_dma_buf(dma_buf);
> > +	return drm_prime_add_buf_handle(prime_fpriv, dma_buf, handle, PRIME_EXPORT);
> > +}
> > +
> > +int drm_prime_lookup_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t *handle)
> >  {
> >  	struct drm_prime_member *member;
> >  
> > @@ -518,19 +540,24 @@ int drm_prime_lookup_imported_buf_handle(struct drm_prime_file_private *prime_fp
> >  	}
> >  	return -ENOENT;
> >  }
> > -EXPORT_SYMBOL(drm_prime_lookup_imported_buf_handle);
> > +EXPORT_SYMBOL(drm_prime_lookup_buf_handle);
> >  
> > -void drm_prime_remove_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf)
> > +void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf)
> >  {
> >  	struct drm_prime_member *member, *safe;
> >  
> >  	mutex_lock(&prime_fpriv->lock);
> >  	list_for_each_entry_safe(member, safe, &prime_fpriv->head, entry) {
> >  		if (member->dma_buf == dma_buf) {
> > +			if (member->type == PRIME_EXPORT)
> > +				dma_buf_put(dma_buf);
> >  			list_del(&member->entry);
> >  			kfree(member);
> >  		}
> >  	}
> >  	mutex_unlock(&prime_fpriv->lock);
> >  }
> > -EXPORT_SYMBOL(drm_prime_remove_imported_buf_handle);
> > +EXPORT_SYMBOL(drm_prime_remove_buf_handle);
> > +
> > +
> > +
> > diff --git a/include/drm/drmP.h b/include/drm/drmP.h
> > index 2d94d74..69712a6 100644
> > --- a/include/drm/drmP.h
> > +++ b/include/drm/drmP.h
> > @@ -1594,8 +1594,8 @@ extern void drm_prime_gem_destroy(struct drm_gem_object *obj, struct sg_table *s
> >  void drm_prime_init_file_private(struct drm_prime_file_private *prime_fpriv);
> >  void drm_prime_destroy_file_private(struct drm_prime_file_private *prime_fpriv);
> >  int drm_prime_add_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t handle);
> > -int drm_prime_lookup_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t *handle);
> > -void drm_prime_remove_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf);
> > +int drm_prime_lookup_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t *handle);
> > +void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf);
> >  
> >  int drm_prime_add_dma_buf(struct drm_device *dev, struct drm_gem_object *obj);
> >  int drm_prime_lookup_obj(struct drm_device *dev, struct dma_buf *buf,
> > -- 
> > 1.8.2
> > 
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