Re: [PATCH 4/5] dma-buf: add dma_buf_(un)map_attachment_locked variants

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Jun 01, 2018 at 02:00:19PM +0200, Christian König wrote:
> Add function variants which can be called with the reservation lock
> already held.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>

I expect that we'll need this patch before patch 3 and then roll it out to
drivers doing reservation locking already, before we can add the
reservation stuff for all other callers.
> ---
>  drivers/dma-buf/dma-buf.c | 60 ++++++++++++++++++++++++++++++++++++++++++-----
>  include/linux/dma-buf.h   |  5 ++++
>  2 files changed, 59 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 4f0708cb58a7..3371509b468e 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -606,6 +606,38 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
>  }
>  EXPORT_SYMBOL_GPL(dma_buf_detach);
>  
> +/**
> + * dma_buf_map_attachment_locked - Maps the buffer into _device_ address space
> + * with the reservation lock held. Is a wrapper for map_dma_buf() of the
> + *
> + * Returns the scatterlist table of the attachment;
> + * dma_buf_ops.
> + * @attach:	[in]	attachment whose scatterlist is to be returned
> + * @direction:	[in]	direction of DMA transfer
> + *
> + * Returns sg_table containing the scatterlist to be returned; returns ERR_PTR
> + * on error. May return -EINTR if it is interrupted by a signal.
> + *
> + * A mapping must be unmapped by using dma_buf_unmap_attachment(). Note that
_locked

Also please reference the other variants here for doc completeness.

> + * the underlying backing storage is pinned for as long as a mapping exists,
> + * therefore users/importers should not hold onto a mapping for undue amounts of
> + * time.
> + */
> +struct sg_table *
> +dma_buf_map_attachment_locked(struct dma_buf_attachment *attach,
> +			      enum dma_data_direction direction)
> +{
> +	struct sg_table *sg_table;
> +
> +	might_sleep();

Needs a lockdep_assert_held here.

> +	sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
> +	if (!sg_table)
> +		sg_table = ERR_PTR(-ENOMEM);
> +
> +	return sg_table;
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_map_attachment_locked);
> +
>  /**
>   * 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
> @@ -626,13 +658,12 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
>  {
>  	struct sg_table *sg_table;
>  
> -	might_sleep();
>  
>  	if (WARN_ON(!attach || !attach->dmabuf))
>  		return ERR_PTR(-EINVAL);
>  
>  	reservation_object_lock(attach->dmabuf->resv, NULL);
> -	sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
> +	sg_table = dma_buf_map_attachment_locked(attach, direction);
>  	reservation_object_unlock(attach->dmabuf->resv);
>  	if (!sg_table)
>  		sg_table = ERR_PTR(-ENOMEM);
> @@ -641,6 +672,26 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
>  }
>  EXPORT_SYMBOL_GPL(dma_buf_map_attachment);
>  
> +/**
> + * dma_buf_unmap_attachment_locked - unmaps the buffer with reservation lock
> + * held, should deallocate the associated scatterlist. Is a wrapper for
> + * unmap_dma_buf() of dma_buf_ops.
> + * @attach:	[in]	attachment to unmap buffer from
> + * @sg_table:	[in]	scatterlist info of the buffer to unmap
> + * @direction:  [in]    direction of DMA transfer
> + *
> + * This unmaps a DMA mapping for @attached obtained by dma_buf_map_attachment().

_locked

> + */
> +void dma_buf_unmap_attachment_locked(struct dma_buf_attachment *attach,
> +				     struct sg_table *sg_table,
> +				     enum dma_data_direction direction)
> +{
> +	might_sleep();

Needs a lockdep_assert_held here.

Otherwise lgtm, but there's the big caveat of that I expect lockdep
fireworks on mass with this, but drivers not yet converted.
-Daniel

> +	attach->dmabuf->ops->unmap_dma_buf(attach, sg_table,
> +						direction);
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment_locked);
> +
>  /**
>   * dma_buf_unmap_attachment - unmaps and decreases usecount of the buffer;might
>   * deallocate the scatterlist associated. Is a wrapper for unmap_dma_buf() of
> @@ -655,14 +706,11 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
>  				struct sg_table *sg_table,
>  				enum dma_data_direction direction)
>  {
> -	might_sleep();
> -
>  	if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
>  		return;
>  
>  	reservation_object_lock(attach->dmabuf->resv, NULL);
> -	attach->dmabuf->ops->unmap_dma_buf(attach, sg_table,
> -						direction);
> +	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/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index d2ba7a027a78..968777e8c662 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -388,8 +388,13 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags);
>  struct dma_buf *dma_buf_get(int fd);
>  void dma_buf_put(struct dma_buf *dmabuf);
>  
> +struct sg_table *dma_buf_map_attachment_locked(struct dma_buf_attachment *,
> +					       enum dma_data_direction);
>  struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
>  					enum dma_data_direction);
> +void dma_buf_unmap_attachment_locked(struct dma_buf_attachment *,
> +				     struct sg_table *,
> +				     enum dma_data_direction);
>  void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,
>  				enum dma_data_direction);
>  int dma_buf_begin_cpu_access(struct dma_buf *dma_buf,
> -- 
> 2.14.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch