block: fix partial IOVA mapping cleanup in blk_rq_dma_map_iova

When dma_iova_link() fails partway through mapping a request's bvec
list, the function breaks out of the loop without cleaning up
already mapped segments. Similarly, if dma_iova_sync() fails after
linking all segments, no cleanup is performed.

This leaves partial IOVA mappings in place. The completion path
attempts to unmap the full expected size via dma_iova_destroy() or
nvme_unmap_data(), but only a partial size was actually mapped,
leading to incorrect unmap operations.

Add an out_unlink error path that calls dma_iova_destroy() to clean
up partial mappings before returning failure. The dma_iova_destroy()
function handles both partial unlink and IOVA space freeing. It
correctly handles the mapped_len == 0 case (first dma_iova_link()
failure) by only freeing the IOVA allocation without attempting to
unmap.

Signed-off-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Chaitanya Kulkarni

block/blk-mq-dma.c

@@ -121,17 +121,20 @@ static bool blk_rq_dma_map_iova(struct request *req, struct device *dma_dev,
 		error = dma_iova_link(dma_dev, state, vec->paddr, mapped,
 				vec->len, dir, attrs);
 		if (error)
-			break;
+			goto out_unlink;
 		mapped += vec->len;
 	} while (blk_map_iter_next(req, &iter->iter, vec));
 
 	error = dma_iova_sync(dma_dev, state, 0, mapped);
-	if (error) {
-		iter->status = errno_to_blk_status(error);
-		return false;
-	}
+	if (error)
+		goto out_unlink;
 
 	return true;
+
+out_unlink:
+	dma_iova_destroy(dma_dev, state, mapped, dir, attrs);
+	iter->status = errno_to_blk_status(error);
+	return false;
 }
 
 static inline void blk_rq_map_iter_init(struct request *rq,