[PATCH v1] udmabuf: Ensure to perform cache synchronisation in begin_cpu_udmabuf()

[Robert Mader]

The message of commit 504e2b4ab97a ("dma-buf/udmabuf: skip redundant cpu sync to
fix cacheline EEXIST warning") says:

> The CPU sync at map/unmap time is also redundant for udmabuf:
> begin_cpu_udmabuf() and end_cpu_udmabuf() already perform explicit
> cache synchronization via dma_sync_sgtable_for_cpu/device() when CPU
> access is requested through the dma-buf interface.

This, however, does not apply to the first time begin_cpu_udmabuf() is
called on an udmabuf, in which case the implementation previously relied on
get_sg_table() to perform the cache synchronisation.

Ensure to call dma_sync_sgtable_for_cpu() in that case as well.

Fixes: 504e2b4ab97a ("dma-buf/udmabuf: skip redundant cpu sync to fix cacheline EEXIST warning")
Signed-off-by: Robert Mader <robert.mader@xxxxxxxxxxxxx>
---
 drivers/dma-buf/udmabuf.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index bced421c0d65..08f57bc1294d 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -224,21 +224,22 @@ static int begin_cpu_udmabuf(struct dma_buf *buf,
 {
 	struct udmabuf *ubuf = buf->priv;
 	struct device *dev = ubuf->device->this_device;
-	int ret = 0;
 
 	if (!ubuf->sg) {
 		ubuf->sg = get_sg_table(dev, buf, direction);
 		if (IS_ERR(ubuf->sg)) {
+			int ret;
+
 			ret = PTR_ERR(ubuf->sg);
 			ubuf->sg = NULL;
+			return ret;
 		} else {
 			ubuf->sg_dir = direction;
 		}
-	} else {
-		dma_sync_sgtable_for_cpu(dev, ubuf->sg, direction);
 	}
 
-	return ret;
+	dma_sync_sgtable_for_cpu(dev, ubuf->sg, direction);
+	return 0;
 }
 
 static int end_cpu_udmabuf(struct dma_buf *buf,
-- 
2.54.0