Re: [PATCH 1/6] dma-buf: add dynamic DMA-buf handling v12

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Hi Christian,

On Tue, Jun 25, 2019 at 02:46:49PM +0200, Christian König wrote:
> On the exporter side we add optional explicit pinning callbacks. If those
> callbacks are implemented the framework no longer caches sg tables and the
> map/unmap callbacks are always called with the lock of the reservation object
> held.
> 
> On the importer side we add an optional invalidate callback. This callback is
> used by the exporter to inform the importers that their mappings should be
> destroyed as soon as possible.
> 
> This allows the exporter to provide the mappings without the need to pin
> the backing store.
> 
> v2: don't try to invalidate mappings when the callback is NULL,
>     lock the reservation obj while using the attachments,
>     add helper to set the callback
> v3: move flag for invalidation support into the DMA-buf,
>     use new attach_info structure to set the callback
> v4: use importer_priv field instead of mangling exporter priv.
> v5: drop invalidation_supported flag
> v6: squash together with pin/unpin changes
> v7: pin/unpin takes an attachment now
> v8: nuke dma_buf_attachment_(map|unmap)_locked,
>     everything is now handled backward compatible
> v9: always cache when export/importer don't agree on dynamic handling
> v10: minimal style cleanup
> v11: drop automatically re-entry avoidance
> v12: rename callback to move_notify
> 
> Signed-off-by: Christian König <christian.koenig@xxxxxxx>
> ---
>  drivers/dma-buf/dma-buf.c | 179 ++++++++++++++++++++++++++++++++++++--
>  include/linux/dma-buf.h   | 108 +++++++++++++++++++++--
>  2 files changed, 273 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 6c15deb5d4ad..216f76109f3f 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -531,6 +531,9 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
>  		return ERR_PTR(-EINVAL);
>  	}
>  
> +	if (WARN_ON(exp_info->ops->cache_sgt_mapping && exp_info->ops->pin))
> +		return ERR_PTR(-EINVAL);
> +
>  	if (!try_module_get(exp_info->owner))
>  		return ERR_PTR(-ENOENT);
>  
> @@ -651,10 +654,12 @@ void dma_buf_put(struct dma_buf *dmabuf)
>  EXPORT_SYMBOL_GPL(dma_buf_put);
>  
>  /**
> - * dma_buf_attach - Add the device to dma_buf's attachments list; optionally,
> + * dma_buf_dynamic_attach - Add the device to dma_buf's attachments list; optionally,
>   * calls attach() of dma_buf_ops to allow device-specific attach functionality
> - * @dmabuf:	[in]	buffer to attach device to.
> - * @dev:	[in]	device to be attached.
> + * @dmabuf:		[in]	buffer to attach device to.
> + * @dev:		[in]	device to be attached.
> + * @importer_ops	[in]	importer operations for the attachment
> + * @importer_priv	[in]	importer private pointer for the attachment
>   *
>   * Returns struct dma_buf_attachment pointer for this attachment. Attachments
>   * must be cleaned up by calling dma_buf_detach().
> @@ -668,8 +673,10 @@ EXPORT_SYMBOL_GPL(dma_buf_put);
>   * accessible to @dev, and cannot be moved to a more suitable place. This is
>   * indicated with the error code -EBUSY.
>   */
> -struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> -					  struct device *dev)
> +struct dma_buf_attachment *
> +dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
> +		       const struct dma_buf_attach_ops *importer_ops,
> +		       void *importer_priv)
>  {
>  	struct dma_buf_attachment *attach;
>  	int ret;
> @@ -683,6 +690,8 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
>  
>  	attach->dev = dev;
>  	attach->dmabuf = dmabuf;
> +	attach->importer_ops = importer_ops;
> +	attach->importer_priv = importer_priv;
>  
>  	mutex_lock(&dmabuf->lock);
>  
> @@ -691,16 +700,72 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
>  		if (ret)
>  			goto err_attach;
>  	}
> +	reservation_object_lock(dmabuf->resv, NULL);
>  	list_add(&attach->node, &dmabuf->attachments);
> +	reservation_object_unlock(dmabuf->resv);
>  
>  	mutex_unlock(&dmabuf->lock);
>  
> +	/* When either the importer or the exporter can't handle dynamic
> +	 * mappings we cache the mapping here to avoid issues with the
> +	 * reservation object lock.
> +	 */
> +	if (dma_buf_attachment_is_dynamic(attach) !=
> +	    dma_buf_is_dynamic(dmabuf)) {
> +		struct sg_table *sgt;
> +
> +		if (dma_buf_is_dynamic(attach->dmabuf)) {
> +			reservation_object_lock(attach->dmabuf->resv, NULL);
> +			ret = dma_buf_pin(attach);
> +			if (ret)
> +				goto err_unlock;
> +		}
> +
> +		sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL);
> +		if (!sgt)
> +			sgt = ERR_PTR(-ENOMEM);
> +		if (IS_ERR(sgt)) {
> +			ret = PTR_ERR(sgt);
> +			goto err_unpin;
> +		}
> +		if (dma_buf_is_dynamic(attach->dmabuf))
> +			reservation_object_unlock(attach->dmabuf->resv);
> +		attach->sgt = sgt;
> +		attach->dir = DMA_BIDIRECTIONAL;
> +	}
> +
>  	return attach;
>  
>  err_attach:
>  	kfree(attach);
>  	mutex_unlock(&dmabuf->lock);
>  	return ERR_PTR(ret);
> +
> +err_unpin:
> +	if (dma_buf_is_dynamic(attach->dmabuf))
> +		dma_buf_unpin(attach);
> +
> +err_unlock:
> +	if (dma_buf_is_dynamic(attach->dmabuf))
> +		reservation_object_unlock(attach->dmabuf->resv);
> +
> +	dma_buf_detach(dmabuf, attach);
> +	return ERR_PTR(ret);
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_dynamic_attach);
> +
> +/**
> + * dma_buf_attach - Wrapper for dma_buf_dynamic_attach
> + * @dmabuf:	[in]	buffer to attach device to.
> + * @dev:	[in]	device to be attached.
> + *
> + * Wrapper to call dma_buf_dynamic_attach() for drivers which still use a static
> + * mapping.
> + */
> +struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> +					  struct device *dev)
> +{
> +	return dma_buf_dynamic_attach(dmabuf, dev, NULL, NULL);
>  }
>  EXPORT_SYMBOL_GPL(dma_buf_attach);
>  
> @@ -717,11 +782,22 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
>  	if (WARN_ON(!dmabuf || !attach))
>  		return;
>  
> -	if (attach->sgt)
> +	if (attach->sgt) {
> +		if (dma_buf_is_dynamic(attach->dmabuf))
> +			reservation_object_lock(attach->dmabuf->resv, NULL);
> +
>  		dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir);
>  
> +		if (dma_buf_is_dynamic(attach->dmabuf)) {
> +			dma_buf_unpin(attach);
> +			reservation_object_unlock(attach->dmabuf->resv);
> +		}
> +	}
> +
>  	mutex_lock(&dmabuf->lock);

Time to ditch dmabuf->lock in favour of the reservation obj? We have a
fallback resv_obj in struct dma_buf already, so this is never null, and I
think would clean up the code a bit.


> +	reservation_object_lock(dmabuf->resv, NULL);
>  	list_del(&attach->node);
> +	reservation_object_unlock(dmabuf->resv);
>  	if (dmabuf->ops->detach)
>  		dmabuf->ops->detach(dmabuf, attach);
>  
> @@ -730,6 +806,44 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
>  }
>  EXPORT_SYMBOL_GPL(dma_buf_detach);
>  
> +/**
> + * dma_buf_pin - Lock down the DMA-buf
> + *
> + * @attach:	[in]	attachment which should be pinned
> + *
> + * Returns:
> + * 0 on success, negative error code on failure.
> + */
> +int dma_buf_pin(struct dma_buf_attachment *attach)
> +{
> +	struct dma_buf *dmabuf = attach->dmabuf;
> +	int ret = 0;
> +
> +	reservation_object_assert_held(dmabuf->resv);
> +
> +	if (dmabuf->ops->pin)
> +		ret = dmabuf->ops->pin(attach);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_pin);
> +
> +/**
> + * dma_buf_unpin - Remove lock from DMA-buf
> + *
> + * @attach:	[in]	attachment which should be unpinned
> + */
> +void dma_buf_unpin(struct dma_buf_attachment *attach)
> +{
> +	struct dma_buf *dmabuf = attach->dmabuf;
> +
> +	reservation_object_assert_held(dmabuf->resv);
> +
> +	if (dmabuf->ops->unpin)
> +		dmabuf->ops->unpin(attach);
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_unpin);
> +
>  /**
>   * dma_buf_map_attachment - Returns the scatterlist table of the attachment;
>   * mapped into _device_ address space. Is a wrapper for map_dma_buf() of the
> @@ -749,6 +863,7 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
>  					enum dma_data_direction direction)
>  {
>  	struct sg_table *sg_table;
> +	int r;
>  
>  	might_sleep();
>  
> @@ -767,10 +882,29 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
>  		return attach->sgt;
>  	}
>  
> +	if (dma_buf_attachment_is_dynamic(attach)) {
> +		reservation_object_assert_held(attach->dmabuf->resv);
> +
> +	} else if (dma_buf_is_dynamic(attach->dmabuf)) {
> +		reservation_object_lock(attach->dmabuf->resv, NULL);
> +		r = dma_buf_pin(attach);
> +		if (r) {
> +			reservation_object_unlock(attach->dmabuf->resv);
> +			return ERR_PTR(r);
> +		}
> +	}

With this design (because we can't cache at attach time unconditionally)
we inflict the reservation lock on all importers. So needs:

	} else {
		/* neither importer nor exporter are dynamice */
		might_lock(dmabuf->resv->ww_mutex);
	}

Same for dma_buf_unmap_attachment.

I also expect that this will blow up in intel-gfx-ci :-/ I did look at
previous intel-gfx-ci runs of your series, and the last one that did pass
was the one that still had the caching in _attach():

Geez I was sooooooooo locking forward to slapping an r-b on this and
volunteering myself to polish the kerneldoc (which isn't great, but also
pre-existing condition plus on my todo list anyway) :-(

> +
>  	sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
>  	if (!sg_table)
>  		sg_table = ERR_PTR(-ENOMEM);
>  
> +	if (!dma_buf_attachment_is_dynamic(attach) &&
> +	    dma_buf_is_dynamic(attach->dmabuf)) {
> +		if (IS_ERR(sg_table))
> +			dma_buf_unpin(attach);
> +		reservation_object_unlock(attach->dmabuf->resv);
> +	}
> +
>  	if (!IS_ERR(sg_table) && attach->dmabuf->ops->cache_sgt_mapping) {
>  		attach->sgt = sg_table;
>  		attach->dir = direction;
> @@ -802,10 +936,41 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
>  	if (attach->sgt == sg_table)
>  		return;
>  
> +	if (dma_buf_attachment_is_dynamic(attach))
> +		reservation_object_assert_held(attach->dmabuf->resv);
> +	else if (dma_buf_is_dynamic(attach->dmabuf))
> +		reservation_object_lock(attach->dmabuf->resv, NULL);
> +
>  	attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
> +
> +	if (dma_buf_is_dynamic(attach->dmabuf) &&
> +	    !dma_buf_attachment_is_dynamic(attach)) {
> +		dma_buf_unpin(attach);
> +		reservation_object_unlock(attach->dmabuf->resv);
> +	}
>  }
>  EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
>  
> +/**
> + * dma_buf_move_notify - notify attachments that DMA-buf is moving
> + *
> + * @dmabuf:	[in]	buffer which is moving
> + *
> + * Informs all attachmenst that they need to destroy and recreated all their
> + * mappings.
> + */
> +void dma_buf_move_notify(struct dma_buf *dmabuf)
> +{
> +	struct dma_buf_attachment *attach;
> +
> +	reservation_object_assert_held(dmabuf->resv);
> +
> +	list_for_each_entry(attach, &dmabuf->attachments, node)
> +		if (attach->importer_ops && attach->importer_ops->move_notify)
> +			attach->importer_ops->move_notify(attach);
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_move_notify);
> +
>  /**
>   * DOC: cpu access
>   *
> @@ -1225,10 +1390,12 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)
>  		seq_puts(s, "\tAttached Devices:\n");
>  		attach_count = 0;
>  
> +		reservation_object_lock(buf_obj->resv, NULL);
>  		list_for_each_entry(attach_obj, &buf_obj->attachments, node) {
>  			seq_printf(s, "\t%s\n", dev_name(attach_obj->dev));
>  			attach_count++;
>  		}
> +		reservation_object_unlock(buf_obj->resv);

Yeah definitely time to retire dmabuf->lock I think.

Cheers, Daniel

>  
>  		seq_printf(s, "Total %d devices attached\n\n",
>  				attach_count);
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index 01ad5b942a6f..ccad2fc1f640 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -92,14 +92,40 @@ struct dma_buf_ops {
>  	 */
>  	void (*detach)(struct dma_buf *, struct dma_buf_attachment *);
>  
> +	/**
> +	 * @pin:
> +	 *
> +	 * This is called by dma_buf_pin and lets the exporter know that the
> +	 * DMA-buf can't be moved any more.
> +	 *
> +	 * This is called with the dmabuf->resv object locked.
> +	 *
> +	 * This callback is optional.
> +	 *
> +	 * Returns:
> +	 *
> +	 * 0 on success, negative error code on failure.
> +	 */
> +	int (*pin)(struct dma_buf_attachment *attach);
> +
> +	/**
> +	 * @unpin:
> +	 *
> +	 * This is called by dma_buf_unpin and lets the exporter know that the
> +	 * DMA-buf can be moved again.
> +	 *
> +	 * This is called with the dmabuf->resv object locked.
> +	 *
> +	 * This callback is optional.
> +	 */
> +	void (*unpin)(struct dma_buf_attachment *attach);
> +
>  	/**
>  	 * @map_dma_buf:
>  	 *
>  	 * This is called by dma_buf_map_attachment() and is used to map a
>  	 * shared &dma_buf into device address space, and it is mandatory. It
> -	 * can only be called if @attach has been called successfully. This
> -	 * essentially pins the DMA buffer into place, and it cannot be moved
> -	 * any more
> +	 * can only be called if @attach has been called successfully.
>  	 *
>  	 * This call may sleep, e.g. when the backing storage first needs to be
>  	 * allocated, or moved to a location suitable for all currently attached
> @@ -120,6 +146,9 @@ struct dma_buf_ops {
>  	 * any other kind of sharing that the exporter might wish to make
>  	 * available to buffer-users.
>  	 *
> +	 * This is always called with the dmabuf->resv object locked when
> +	 * the pin/unpin callbacks are implemented.
> +	 *
>  	 * Returns:
>  	 *
>  	 * A &sg_table scatter list of or the backing storage of the DMA buffer,
> @@ -137,9 +166,6 @@ struct dma_buf_ops {
>  	 *
>  	 * This is called by dma_buf_unmap_attachment() and should unmap and
>  	 * release the &sg_table allocated in @map_dma_buf, and it is mandatory.
> -	 * It should also unpin the backing storage if this is the last mapping
> -	 * of the DMA buffer, it the exporter supports backing storage
> -	 * migration.
>  	 */
>  	void (*unmap_dma_buf)(struct dma_buf_attachment *,
>  			      struct sg_table *,
> @@ -330,6 +356,34 @@ struct dma_buf {
>  	} cb_excl, cb_shared;
>  };
>  
> +/**
> + * struct dma_buf_attach_ops - importer operations for an attachment
> + * @move_notify: [optional] notification that the DMA-buf is moving
> + *
> + * Attachment operations implemented by the importer.
> + */
> +struct dma_buf_attach_ops {
> +	/**
> +	 * @move_notify
> +	 *
> +	 * If this callback is provided the framework can avoid pinning the
> +	 * backing store while mappings exists.
> +	 *
> +	 * This callback is called with the lock of the reservation object
> +	 * associated with the dma_buf held and the mapping function must be
> +	 * called with this lock held as well. This makes sure that no mapping
> +	 * is created concurrently with an ongoing move operation.
> +	 *
> +	 * Mappings stay valid and are not directly affected by this callback.
> +	 * But the DMA-buf can now be in a different physical location, so all
> +	 * mappings should be destroyed and re-created as soon as possible.
> +	 *
> +	 * New mappings can be created after this callback returns, and will
> +	 * point to the new location of the DMA-buf.
> +	 */
> +	void (*move_notify)(struct dma_buf_attachment *attach);
> +};
> +
>  /**
>   * struct dma_buf_attachment - holds device-buffer attachment data
>   * @dmabuf: buffer for this attachment.
> @@ -338,6 +392,8 @@ struct dma_buf {
>   * @sgt: cached mapping.
>   * @dir: direction of cached mapping.
>   * @priv: exporter specific attachment data.
> + * @importer_ops: importer operations for this attachment.
> + * @importer_priv: importer specific attachment data.
>   *
>   * This structure holds the attachment information between the dma_buf buffer
>   * and its user device(s). The list contains one attachment struct per device
> @@ -355,6 +411,9 @@ struct dma_buf_attachment {
>  	struct sg_table *sgt;
>  	enum dma_data_direction dir;
>  	void *priv;
> +
> +	const struct dma_buf_attach_ops *importer_ops;
> +	void *importer_priv;
>  };
>  
>  /**
> @@ -405,10 +464,42 @@ static inline void get_dma_buf(struct dma_buf *dmabuf)
>  	get_file(dmabuf->file);
>  }
>  
> +/**
> + * dma_buf_is_dynamic - check if a DMA-buf uses dynamic mappings.
> + * @dmabuf: the DMA-buf to check
> + *
> + * Returns true if a DMA-buf exporter wants to create dynamic sg table mappings
> + * for each attachment. False if only a single static sg table should be used.
> + */
> +static inline bool dma_buf_is_dynamic(struct dma_buf *dmabuf)
> +{
> +	return !!dmabuf->ops->pin;
> +}
> +
> +/**
> + * dma_buf_attachment_is_dynamic - check if a DMA-buf attachment uses dynamic
> + * mappinsg
> + * @attach: the DMA-buf attachment to check
> + *
> + * Returns true if a DMA-buf importer wants to use dynamic sg table mappings and
> + * calls the map/unmap functions with the reservation object locked.
> + */
> +static inline bool
> +dma_buf_attachment_is_dynamic(struct dma_buf_attachment *attach)
> +{
> +	return attach->importer_ops && attach->importer_ops->move_notify;
> +}
> +
>  struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> -							struct device *dev);
> +					  struct device *dev);
> +struct dma_buf_attachment *
> +dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
> +		       const struct dma_buf_attach_ops *importer_ops,
> +		       void *importer_priv);
>  void dma_buf_detach(struct dma_buf *dmabuf,
> -				struct dma_buf_attachment *dmabuf_attach);
> +		    struct dma_buf_attachment *attach);
> +int dma_buf_pin(struct dma_buf_attachment *attach);
> +void dma_buf_unpin(struct dma_buf_attachment *attach);
>  
>  struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info);
>  
> @@ -420,6 +511,7 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
>  					enum dma_data_direction);
>  void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,
>  				enum dma_data_direction);
> +void dma_buf_move_notify(struct dma_buf *dma_buf);
>  int dma_buf_begin_cpu_access(struct dma_buf *dma_buf,
>  			     enum dma_data_direction dir);
>  int dma_buf_end_cpu_access(struct dma_buf *dma_buf,
> -- 
> 2.17.1
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx

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