drbd: Create new current UUID as late as possible

The choice was to either delay creation of the new UUID until
IO got thawed or to delay it until the first IO request.

Both are correct, the later is more friendly to users of
dual-primary setups, that actually only write on one side.

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

1 files changed, 8 insertions, 1 deletions

diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index c194348a46ed..e9654c8d5b62 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -943,7 +943,8 @@ struct drbd_conf {
         struct drbd_work  resync_work,
                           unplug_work,
                           md_sync_work,
-                          delay_probe_work;
+                          delay_probe_work,
+                          uuid_work;
         struct timer_list resync_timer;
         struct timer_list md_sync_timer;
         struct timer_list delay_probe_timer;
@@ -1068,6 +1069,7 @@ struct drbd_conf {
         struct timeval dps_time; /* delay-probes-start-time */
         unsigned int dp_volume_last;  /* send_cnt of last delay probe */
         int c_sync_rate; /* current resync rate after delay_probe magic */
+        atomic_t new_c_uuid;
 };
 
 static inline struct drbd_conf *minor_to_mdev(unsigned int minor)
@@ -2217,6 +2219,8 @@ static inline int __inc_ap_bio_cond(struct drbd_conf *mdev)
                 return 0;
         if (test_bit(BITMAP_IO, &mdev->flags))
                 return 0;
+        if (atomic_read(&mdev->new_c_uuid))
+                return 0;
         return 1;
 }
 
@@ -2237,6 +2241,9 @@ static inline void inc_ap_bio(struct drbd_conf *mdev, int count)
          * to avoid races with the reconnect code,
          * we need to atomic_inc within the spinlock. */
 
+        if (atomic_read(&mdev->new_c_uuid) && atomic_add_unless(&mdev->new_c_uuid, -1, 1))
+                drbd_queue_work_front(&mdev->data.work, &mdev->uuid_work);
+
         spin_lock_irq(&mdev->req_lock);
         while (!__inc_ap_bio_cond(mdev)) {
                 prepare_to_wait(&mdev->misc_wait, &wait, TASK_UNINTERRUPTIBLE);