Re: [PATCH 1/4] dma-buf: add dma_buf_(un)map_attachment_locked variants v2

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Am 28.06.2018 um 11:53 schrieb Zhang, Jerry (Junwei):
> On 06/22/2018 10:11 PM, Christian König wrote:
>> Add function variants which can be called with the reservation lock
>> already held.
>>
>> v2: reordered, add lockdep asserts, fix kerneldoc
>>
>> Signed-off-by: Christian König <christian.koenig@amd.com>
>> ---
>>   drivers/dma-buf/dma-buf.c | 57 
>> +++++++++++++++++++++++++++++++++++++++++++++++
>>   include/linux/dma-buf.h   |  5 +++++
>>   2 files changed, 62 insertions(+)
>>
>> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
>> index 852a3928ee71..dc94e76e2e2a 100644
>> --- a/drivers/dma-buf/dma-buf.c
>> +++ b/drivers/dma-buf/dma-buf.c
>> @@ -606,6 +606,40 @@ 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_locked(). Note
>> + * that 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;
>> +
>
> Perhaps better to add some error check, like dma_buf_map_attachment()
>
> WARN_ON(!attach || !attach->dmabuf)

Actually I wanted to remove those from the other functions as well.

WARN_ON and BUG_ON checks for NULL pointers before using them are 
totally pointless because they have the same effect as a crash.

Regards,
Christian.

>
> Apart from that, it's
> Reviewed-by: Junwei Zhang <Jerry.Zhang@amd.com>
>
> Jerry
>
>> +    might_sleep();
>> +    reservation_object_assert_held(attach->dmabuf->resv);
>> +
>> +    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
>> @@ -639,6 +673,29 @@ 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();
>> +    reservation_object_assert_held(attach->dmabuf->resv);
>> +
>> +    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
>> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
>> index 991787a03199..a25e754ae2f7 100644
>> --- a/include/linux/dma-buf.h
>> +++ b/include/linux/dma-buf.h
>> @@ -384,8 +384,13 @@ 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,
>>

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