[PATCH] brd: fix brd_rw_page() vs copy_to_brd_setup errors

[Dan Williams]

As is done in zram_rw_page, pmem_rw_page, and btt_rw_page, don't
call page_endio in the error case since do_mpage_readpage and
__mpage_writepage will resubmit on error. Calling page_endio in the
error case leads to double completion.

Cc: Jens Axboe <ax...@kernel.dk>
Cc: Matthew Wilcox <mawil...@microsoft.com>
Cc: Ross Zwisler <ross.zwis...@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
---
Noticed this while looking at unrelated brd code...

 drivers/block/brd.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 104b71c0490d..055255ea131d 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -327,7 +327,13 @@ static int brd_rw_page(struct block_device *bdev, sector_t 
sector,
 {
        struct brd_device *brd = bdev->bd_disk->private_data;
        int err = brd_do_bvec(brd, page, PAGE_SIZE, 0, is_write, sector);
-       page_endio(page, is_write, err);
+
+       /*
+        * In the error case we expect the upper layer to retry, so we
+        * can't trigger page_endio yet.
+        */
+       if (err == 0)
+               page_endio(page, is_write, 0);
        return err;
 }