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>

1 files changed, 1 insertions, 4 deletions

diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 23878ffc43c8..73c905d0ef18 100644
--- 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);
         }