Re: [PATCH 03/12] dma-buf: lock the reservation object during (un)map_dma_buf v3

[Daniel Vetter]

On Tue, Apr 16, 2019 at 08:38:32PM +0200, Christian König wrote:
> Make it mandatory for dynamic dma-buf callbacks to be called with the
> reservation lock held.
> 
> For static dma-buf exporters we still have the fallback of using cached sgt.
> 
> v2: reordered
> v3: rebased on sgt caching
> v4: use the cached sgt when possible
> 
> Signed-off-by: Christian König <christian.koenig@xxxxxxx>

I think there's a bit a rebase chaos going on:
- some comments left behind with no_sgt_cache, which I can't find anymore
- the function signature rework of dma_buf_attach should imo be split out

Next issue is that the reservation object locking is still in the path of
dma_buf_map, so probably still going to result in tons of lockdep splats.
Except the i915+amdgpu path should now work due to the fastpath.

Not sure that's a solution that really works, just hides that
fundamentally we still have that issue of incompatible locking chains
between different drivers.
-Daniel

> ---
>  drivers/dma-buf/dma-buf.c                     | 24 ++++++++++---------
>  drivers/gpu/drm/armada/armada_gem.c           |  6 ++++-
>  drivers/gpu/drm/drm_prime.c                   |  6 ++++-
>  drivers/gpu/drm/i915/i915_gem_dmabuf.c        |  6 ++++-
>  drivers/gpu/drm/tegra/gem.c                   |  6 ++++-
>  drivers/gpu/drm/udl/udl_dmabuf.c              |  6 ++++-
>  .../common/videobuf2/videobuf2-dma-contig.c   |  6 ++++-
>  .../media/common/videobuf2/videobuf2-dma-sg.c |  6 ++++-
>  drivers/staging/media/tegra-vde/tegra-vde.c   |  6 ++++-
>  include/linux/dma-buf.h                       | 23 ++++++++++++++++--
>  10 files changed, 74 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index ef480e5fb239..83c92bfd964c 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -532,8 +532,9 @@ EXPORT_SYMBOL_GPL(dma_buf_put);
>  /**
>   * dma_buf_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.
> + * @info:	[in]	holds all the attach related information provided
> + *			by the importer. see &struct dma_buf_attach_info
> + *			for further details.
>   *
>   * Returns struct dma_buf_attachment pointer for this attachment. Attachments
>   * must be cleaned up by calling dma_buf_detach().
> @@ -547,20 +548,20 @@ 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_attach(const struct dma_buf_attach_info *info)
>  {
> +	struct dma_buf *dmabuf = info->dmabuf;
>  	struct dma_buf_attachment *attach;
>  	int ret;
>  
> -	if (WARN_ON(!dmabuf || !dev))
> +	if (WARN_ON(!dmabuf || !info->dev))
>  		return ERR_PTR(-EINVAL);
>  
>  	attach = kzalloc(sizeof(*attach), GFP_KERNEL);
>  	if (!attach)
>  		return ERR_PTR(-ENOMEM);
>  
> -	attach->dev = dev;
> +	attach->dev = info->dev;
>  	attach->dmabuf = dmabuf;
>  
>  	mutex_lock(&dmabuf->lock);
> @@ -688,9 +689,9 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
>  	if (attach->sgt)
>  		return attach->sgt;
>  
> -	sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
> -	if (!sg_table)
> -		sg_table = ERR_PTR(-ENOMEM);
> +	reservation_object_lock(attach->dmabuf->resv, NULL);
> +	sg_table = dma_buf_map_attachment_locked(attach, direction);
> +	reservation_object_unlock(attach->dmabuf->resv);
>  
>  	return sg_table;
>  }
> @@ -744,8 +745,9 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
>  	if (attach->sgt == sg_table)
>  		return;
>  
> -	attach->dmabuf->ops->unmap_dma_buf(attach, sg_table,
> -						direction);
> +	reservation_object_lock(attach->dmabuf->resv, NULL);
> +	dma_buf_unmap_attachment_locked(attach, sg_table, direction);
> +	reservation_object_unlock(attach->dmabuf->resv);
>  }
>  EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
>  
> diff --git a/drivers/gpu/drm/armada/armada_gem.c b/drivers/gpu/drm/armada/armada_gem.c
> index 642d0e70d0f8..19c47821032f 100644
> --- a/drivers/gpu/drm/armada/armada_gem.c
> +++ b/drivers/gpu/drm/armada/armada_gem.c
> @@ -501,6 +501,10 @@ armada_gem_prime_export(struct drm_device *dev, struct drm_gem_object *obj,
>  struct drm_gem_object *
>  armada_gem_prime_import(struct drm_device *dev, struct dma_buf *buf)
>  {
> +	struct dma_buf_attach_info attach_info = {
> +		.dev = dev->dev,
> +		.dmabuf = buf
> +	};
>  	struct dma_buf_attachment *attach;
>  	struct armada_gem_object *dobj;
>  
> @@ -516,7 +520,7 @@ armada_gem_prime_import(struct drm_device *dev, struct dma_buf *buf)
>  		}
>  	}
>  
> -	attach = dma_buf_attach(buf, dev->dev);
> +	attach = dma_buf_attach(&attach_info);
>  	if (IS_ERR(attach))
>  		return ERR_CAST(attach);
>  
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index 231e3f6d5f41..1fadf5d5ed33 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -709,6 +709,10 @@ struct drm_gem_object *drm_gem_prime_import_dev(struct drm_device *dev,
>  					    struct dma_buf *dma_buf,
>  					    struct device *attach_dev)
>  {
> +	struct dma_buf_attach_info attach_info = {
> +		.dev = attach_dev,
> +		.dmabuf = dma_buf
> +	};
>  	struct dma_buf_attachment *attach;
>  	struct sg_table *sgt;
>  	struct drm_gem_object *obj;
> @@ -729,7 +733,7 @@ struct drm_gem_object *drm_gem_prime_import_dev(struct drm_device *dev,
>  	if (!dev->driver->gem_prime_import_sg_table)
>  		return ERR_PTR(-EINVAL);
>  
> -	attach = dma_buf_attach(dma_buf, attach_dev);
> +	attach = dma_buf_attach(&attach_info);
>  	if (IS_ERR(attach))
>  		return ERR_CAST(attach);
>  
> diff --git a/drivers/gpu/drm/i915/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
> index 82e2ca17a441..aa7f685bd6ca 100644
> --- a/drivers/gpu/drm/i915/i915_gem_dmabuf.c
> +++ b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
> @@ -277,6 +277,10 @@ static const struct drm_i915_gem_object_ops i915_gem_object_dmabuf_ops = {
>  struct drm_gem_object *i915_gem_prime_import(struct drm_device *dev,
>  					     struct dma_buf *dma_buf)
>  {
> +	struct dma_buf_attach_info attach_info = {
> +		.dev = dev->dev,
> +		.dmabuf = dma_buf
> +	};
>  	struct dma_buf_attachment *attach;
>  	struct drm_i915_gem_object *obj;
>  	int ret;
> @@ -295,7 +299,7 @@ struct drm_gem_object *i915_gem_prime_import(struct drm_device *dev,
>  	}
>  
>  	/* need to attach */
> -	attach = dma_buf_attach(dma_buf, dev->dev);
> +	attach = dma_buf_attach(&attach_info);
>  	if (IS_ERR(attach))
>  		return ERR_CAST(attach);
>  
> diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
> index 4f80100ff5f3..8e6b6c879add 100644
> --- a/drivers/gpu/drm/tegra/gem.c
> +++ b/drivers/gpu/drm/tegra/gem.c
> @@ -332,6 +332,10 @@ struct tegra_bo *tegra_bo_create_with_handle(struct drm_file *file,
>  static struct tegra_bo *tegra_bo_import(struct drm_device *drm,
>  					struct dma_buf *buf)
>  {
> +	struct dma_buf_attach_info attach_info = {
> +		.dev = drm->dev,
> +		.dmabuf = buf
> +	};
>  	struct tegra_drm *tegra = drm->dev_private;
>  	struct dma_buf_attachment *attach;
>  	struct tegra_bo *bo;
> @@ -341,7 +345,7 @@ static struct tegra_bo *tegra_bo_import(struct drm_device *drm,
>  	if (IS_ERR(bo))
>  		return bo;
>  
> -	attach = dma_buf_attach(buf, drm->dev);
> +	attach = dma_buf_attach(&attach_info);
>  	if (IS_ERR(attach)) {
>  		err = PTR_ERR(attach);
>  		goto free;
> diff --git a/drivers/gpu/drm/udl/udl_dmabuf.c b/drivers/gpu/drm/udl/udl_dmabuf.c
> index 556f62662aa9..86b928f9742f 100644
> --- a/drivers/gpu/drm/udl/udl_dmabuf.c
> +++ b/drivers/gpu/drm/udl/udl_dmabuf.c
> @@ -226,6 +226,10 @@ static int udl_prime_create(struct drm_device *dev,
>  struct drm_gem_object *udl_gem_prime_import(struct drm_device *dev,
>  				struct dma_buf *dma_buf)
>  {
> +	struct dma_buf_attach_info attach_info = {
> +		.dev = dev->dev,
> +		.dmabuf = dma_buf
> +	};
>  	struct dma_buf_attachment *attach;
>  	struct sg_table *sg;
>  	struct udl_gem_object *uobj;
> @@ -233,7 +237,7 @@ struct drm_gem_object *udl_gem_prime_import(struct drm_device *dev,
>  
>  	/* need to attach */
>  	get_device(dev->dev);
> -	attach = dma_buf_attach(dma_buf, dev->dev);
> +	attach = dma_buf_attach(&attach_info);
>  	if (IS_ERR(attach)) {
>  		put_device(dev->dev);
>  		return ERR_CAST(attach);
> diff --git a/drivers/media/common/videobuf2/videobuf2-dma-contig.c b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> index aff0ab7bf83d..1f2687b5eb0e 100644
> --- a/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> +++ b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> @@ -676,6 +676,10 @@ static void vb2_dc_detach_dmabuf(void *mem_priv)
>  static void *vb2_dc_attach_dmabuf(struct device *dev, struct dma_buf *dbuf,
>  	unsigned long size, enum dma_data_direction dma_dir)
>  {
> +	struct dma_buf_attach_info attach_info = {
> +		.dev = dev,
> +		.dmabuf = dbuf
> +	};
>  	struct vb2_dc_buf *buf;
>  	struct dma_buf_attachment *dba;
>  
> @@ -691,7 +695,7 @@ static void *vb2_dc_attach_dmabuf(struct device *dev, struct dma_buf *dbuf,
>  
>  	buf->dev = dev;
>  	/* create attachment for the dmabuf with the user device */
> -	dba = dma_buf_attach(dbuf, buf->dev);
> +	dba = dma_buf_attach(&attach_info);
>  	if (IS_ERR(dba)) {
>  		pr_err("failed to attach dmabuf\n");
>  		kfree(buf);
> diff --git a/drivers/media/common/videobuf2/videobuf2-dma-sg.c b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
> index 015e737095cd..cbd626d2393a 100644
> --- a/drivers/media/common/videobuf2/videobuf2-dma-sg.c
> +++ b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
> @@ -608,6 +608,10 @@ static void vb2_dma_sg_detach_dmabuf(void *mem_priv)
>  static void *vb2_dma_sg_attach_dmabuf(struct device *dev, struct dma_buf *dbuf,
>  	unsigned long size, enum dma_data_direction dma_dir)
>  {
> +	struct dma_buf_attach_info attach_info = {
> +		.dev = dev,
> +		.dmabuf = dbuf
> +	};
>  	struct vb2_dma_sg_buf *buf;
>  	struct dma_buf_attachment *dba;
>  
> @@ -623,7 +627,7 @@ static void *vb2_dma_sg_attach_dmabuf(struct device *dev, struct dma_buf *dbuf,
>  
>  	buf->dev = dev;
>  	/* create attachment for the dmabuf with the user device */
> -	dba = dma_buf_attach(dbuf, buf->dev);
> +	dba = dma_buf_attach(&attach_info);
>  	if (IS_ERR(dba)) {
>  		pr_err("failed to attach dmabuf\n");
>  		kfree(buf);
> diff --git a/drivers/staging/media/tegra-vde/tegra-vde.c b/drivers/staging/media/tegra-vde/tegra-vde.c
> index aa6c6bba961e..5a10c1facc27 100644
> --- a/drivers/staging/media/tegra-vde/tegra-vde.c
> +++ b/drivers/staging/media/tegra-vde/tegra-vde.c
> @@ -568,6 +568,10 @@ static int tegra_vde_attach_dmabuf(struct device *dev,
>  				   size_t *size,
>  				   enum dma_data_direction dma_dir)
>  {
> +	struct dma_buf_attach_info attach_info = {
> +		.dev = dev,
> +		.dmabuf = dmabuf
> +	};
>  	struct dma_buf_attachment *attachment;
>  	struct dma_buf *dmabuf;
>  	struct sg_table *sgt;
> @@ -591,7 +595,7 @@ static int tegra_vde_attach_dmabuf(struct device *dev,
>  		return -EINVAL;
>  	}
>  
> -	attachment = dma_buf_attach(dmabuf, dev);
> +	attachment = dma_buf_attach(&attach_info);
>  	if (IS_ERR(attachment)) {
>  		dev_err(dev, "Failed to attach dmabuf\n");
>  		err = PTR_ERR(attachment);
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index 18a78be53541..7e23758db3a4 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -128,6 +128,9 @@ 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
> +	 * no_sgt_cache is true.
> +	 *
>  	 * Returns:
>  	 *
>  	 * A &sg_table scatter list of or the backing storage of the DMA buffer,
> @@ -148,6 +151,9 @@ struct dma_buf_ops {
>  	 * It should also unpin the backing storage if this is the last mapping
>  	 * of the DMA buffer, it the exporter supports backing storage
>  	 * migration.
> +	 *
> +	 * This is always called with the dmabuf->resv object locked when
> +	 * no_sgt_cache is true.
>  	 */
>  	void (*unmap_dma_buf)(struct dma_buf_attachment *,
>  			      struct sg_table *,
> @@ -370,6 +376,19 @@ struct dma_buf_export_info {
>  	struct dma_buf_export_info name = { .exp_name = KBUILD_MODNAME, \
>  					 .owner = THIS_MODULE }
>  
> +/**
> + * struct dma_buf_attach_info - holds information needed to attach to a dma_buf
> + * @dmabuf:	the exported dma_buf
> + * @dev:	the device which wants to import the attachment
> + *
> + * This structure holds the information required to attach to a buffer. Used
> + * with dma_buf_attach() only.
> + */
> +struct dma_buf_attach_info {
> +	struct dma_buf *dmabuf;
> +	struct device *dev;
> +};
> +
>  /**
>   * get_dma_buf - convenience wrapper for get_file.
>   * @dmabuf:	[in]	pointer to dma_buf
> @@ -384,8 +403,8 @@ static inline void get_dma_buf(struct dma_buf *dmabuf)
>  	get_file(dmabuf->file);
>  }
>  
> -struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> -							struct device *dev);
> +struct dma_buf_attachment *
> +dma_buf_attach(const struct dma_buf_attach_info *info);
>  void dma_buf_detach(struct dma_buf *dmabuf,
>  				struct dma_buf_attachment *dmabuf_attach);
>  
> -- 
> 2.17.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch