drbd: fix race on meta-data update

The race:
	drbd_md_mark_dirty()
	drbd_md_sync()
		if (!test_and_clear_bit(MD_DIRTY, &mdev->flags))
			return;
		drbd_md_sync_page_io(mdev, mdev->ldev, sector, WRITE)
  ==> RACE
		clear_bit(MD_DIRTY, &mdev->flags); <== spurious

Fixed by removing the spurious clear_bit.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 23878ffc43c8ac588ea4060e83d38724eff02a7d..73c905d0ef181bd95e0298ccf0d5aaa2dc73209d 100644 (file)
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -3446,12 +3446,9 @@ void drbd_md_sync(struct drbd_conf *mdev)
        D_ASSERT(drbd_md_ss__(mdev, mdev->ldev) == mdev->ldev->md.md_offset);
        sector = mdev->ldev->md.md_offset;
 
-       if (drbd_md_sync_page_io(mdev, mdev->ldev, sector, WRITE)) {
-               clear_bit(MD_DIRTY, &mdev->flags);
-       } else {
+       if (!drbd_md_sync_page_io(mdev, mdev->ldev, sector, WRITE)) {
                /* this was a try anyways ... */
                dev_err(DEV, "meta data update failed!\n");
-
                drbd_chk_io_error(mdev, 1, TRUE);
        }