rapidio: fix an error in get_user_pages_fast() error handling

In the case of get_user_pages_fast() returning fewer pages than
requested, rio_dma_transfer() does not quite do the right thing.  It
attempts to release all the pages that were requested, rather than just
the pages that were pinned.

Fix the error handling so that only the pages that were successfully
pinned are released.

Fixes: e8de370188 ("rapidio: add mport char device driver")
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: Alexandre Bounine <alex.bou9@gmail.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200517235620.205225-2-jhubbard@nvidia.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rapidio/devices/rio_mport_cdev.c

@@ -877,6 +877,11 @@ rio_dma_transfer(struct file *filp, u32 transfer_mode,
 				rmcd_error("pinned %ld out of %ld pages",
 					   pinned, nr_pages);
 			ret = -EFAULT;
+			/*
+			 * Set nr_pages up to mean "how many pages to unpin, in
+			 * the error handler:
+			 */
+			nr_pages = pinned;
 			goto err_pg;
 		}