--- x/drivers/dma-buf/udmabuf.c
+++ y/drivers/dma-buf/udmabuf.c
@@ -153,7 +153,12 @@ static int begin_cpu_udmabuf(struct dma_
 	int ret = 0;
 
 	if (!ubuf->sg) {
-		ubuf->sg = get_sg_table(dev, buf, direction);
+		static DEFINE_MUTEX(lock);
+
+		mutex_lock(&lock);
+		if (!ubuf->sg)
+			ubuf->sg = get_sg_table(dev, buf, direction);
+		mutex_unlock(&lock);
 		if (IS_ERR(ubuf->sg)) {
 			ret = PTR_ERR(ubuf->sg);
 			ubuf->sg = NULL;