[PATCH] dma-buf: Use dma_fence_unwrap_for_each when importing fences

[Christian König]

Am 02.08.22 um 23:01 schrieb Jason Ekstrand:
> Ever since 68129f431faa ("dma-buf: warn about containers in dma_resv object"),
> dma_resv_add_shared_fence will warn if you attempt to add a container fence.
> While most drivers were fine, fences can also be added to a dma_resv via the
> recently added DMA_BUF_IOCTL_IMPORT_SYNC_FILE.  Use dma_fence_unwrap_for_each
> to add each fence one at a time.
>
> Fixes: 594740497e99 ("dma-buf: Add an API for importing sync files (v10)")
> Signed-off-by: Jason Ekstrand <jason.ekstrand at collabora.com>
> Reported-by: Sarah Walker <Sarah.Walker at imgtec.com>
> Cc: Christian König <christian.koenig at amd.com>
> ---
>   drivers/dma-buf/dma-buf.c | 23 +++++++++++++++++------
>   1 file changed, 17 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 630133284e2b..8d5d45112f52 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -15,6 +15,7 @@
>   #include <linux/slab.h>
>   #include <linux/dma-buf.h>
>   #include <linux/dma-fence.h>
> +#include <linux/dma-fence-unwrap.h>
>   #include <linux/anon_inodes.h>
>   #include <linux/export.h>
>   #include <linux/debugfs.h>
> @@ -391,8 +392,10 @@ static long dma_buf_import_sync_file(struct dma_buf *dmabuf,
>   				     const void __user *user_data)
>   {
>   	struct dma_buf_import_sync_file arg;
> -	struct dma_fence *fence;
> +	struct dma_fence *fence, *f;
>   	enum dma_resv_usage usage;
> +	struct dma_fence_unwrap iter;
> +	unsigned int num_fences;
>   	int ret = 0;
>   
>   	if (copy_from_user(&arg, user_data, sizeof(arg)))
> @@ -411,13 +414,21 @@ static long dma_buf_import_sync_file(struct dma_buf *dmabuf,
>   	usage = (arg.flags & DMA_BUF_SYNC_WRITE) ? DMA_RESV_USAGE_WRITE :
>   						   DMA_RESV_USAGE_READ;
>   
> -	dma_resv_lock(dmabuf->resv, NULL);
> +	num_fences = 0;
> +	dma_fence_unwrap_for_each(f, &iter, fence)
> +		++num_fences;
>   
> -	ret = dma_resv_reserve_fences(dmabuf->resv, 1);
> -	if (!ret)
> -		dma_resv_add_fence(dmabuf->resv, fence, usage);
> +	if (num_fences > 0) {
> +		dma_resv_lock(dmabuf->resv, NULL);
>   
> -	dma_resv_unlock(dmabuf->resv);
> +		ret = dma_resv_reserve_fences(dmabuf->resv, num_fences);

That looks like it is misplaced.

You *must* only lock the reservation object once and then add all fences 
in one go.

Thinking now about it we probably had a bug around that before as well. 
Going to double check tomorrow.

Regards,
Christian.

> +		if (!ret) {
> +			dma_fence_unwrap_for_each(f, &iter, fence)
> +				dma_resv_add_fence(dmabuf->resv, f, usage);
> +		}
> +
> +		dma_resv_unlock(dmabuf->resv);
> +	}
>   
>   	dma_fence_put(fence);
>