dma-buf: Use dma_fence_unwrap_for_each when importing fences

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 <[e-mail]>
Reported-by: Sarah Walker <[e-mail]>
Reviewed-by: Christian König <[e-mail]>
CC: [e-mail]
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Signed-off-by: Christian König <[e-mail]>

drivers/dma-buf/dma-buf.c

···
 #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>
···
 				     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)))
···
 	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);
+		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);