drbd: Fixes from the drbd-8.3 branch

* drbd-8.3:
  drbd: fix spurious meta data IO "error"
  drbd: Fixed a race condition between detach and start of resync
  drbd: fix harmless race to not trigger an ASSERT
  drbd: Derive sync-UUIDs only from the bitmap-uuid if it is non-zero
  drbd: Fixed current UUID generation (regression introduced recently, after 8.3.11)

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

1 files changed, 14 insertions, 2 deletions

diff --git a/drivers/block/drbd/drbd_worker.c b/drivers/block/drbd/drbd_worker.c
index 34a6065d95e6..bc2cfd6c600f 100644
--- a/drivers/block/drbd/drbd_worker.c
+++ b/drivers/block/drbd/drbd_worker.c
@@ -74,10 +74,21 @@ void drbd_md_io_complete(struct bio *bio, int error)
 
 	md_io->error = error;
 
+	/* We grabbed an extra reference in _drbd_md_sync_page_io() to be able
+	 * to timeout on the lower level device, and eventually detach from it.
+	 * If this io completion runs after that timeout expired, this
+	 * drbd_md_put_buffer() may allow us to finally try and re-attach.
+	 * During normal operation, this only puts that extra reference
+	 * down to 1 again.
+	 * Make sure we first drop the reference, and only then signal
+	 * completion, or we may (in drbd_al_read_log()) cycle so fast into the
+	 * next drbd_md_sync_page_io(), that we trigger the
+	 * ASSERT(atomic_read(&mdev->md_io_in_use) == 1) there.
+	 */
+	drbd_md_put_buffer(mdev);
 	md_io->done = 1;
 	wake_up(&mdev->misc_wait);
 	bio_put(bio);
-	drbd_md_put_buffer(mdev);
 	put_ldev(mdev);
 }
 
@@ -1581,12 +1592,13 @@ void drbd_start_resync(struct drbd_conf *mdev, enum drbd_conns side)
 	}
 	clear_bit(B_RS_H_DONE, &mdev->flags);
 
+	write_lock_irq(&global_state_lock);
 	if (!get_ldev_if_state(mdev, D_NEGOTIATING)) {
+		write_unlock_irq(&global_state_lock);
 		mutex_unlock(mdev->state_mutex);
 		return;
 	}
 
-	write_lock_irq(&global_state_lock);
 	ns = drbd_read_state(mdev);
 
 	ns.aftr_isp = !_drbd_may_sync_now(mdev);