[DRBD-user] Is it normal that we only got 20% success rate of removing the primary node?

[刘丹]

Hi everyone,
I have a question about removing the primary node with DRBD9.
"Is it normal that we only got 20% success rate of removing the primary node?"
Version of DRBD kernel source is the newest version(9.0.4-1).Version of DRBD utils is 8.9.6.
Description:
    3 nodes, one of the nodes is primary,disk state is UpToDate.
    I got an error message 'State change failed: (-2) Need access to UpToDate data' when executing the command 'drbdadm down <res-name>' on the primary node.
    After excuting the command for the first time, the status of the primary node is the following:
    # drbdadm status r0
        r0 role:Secondary
        disk:UpToDate
    After executing the command for the second time,the status of the primary node is empty, then the primary node is removed successfully the time.
    # drbdadm status r0
    <NOTHING TO PRINT>.

Analysis:
    We found the following code that report the error.
    __is_valid_soft_transition()
    {
        ...
        if (device->open_ro_cnt && any_disk_up_to_date[OLD] && !any_disk_up_to_date[NEW]){
                    return SS_NO_UP_TO_DATE_DISK;
                }
        ...
    }
    
    Then we done 20 runs of the test:
    1)start the node
    2)promote the node
    3)remove the node(drbdadm down <res-name>)
    Only got a 20% success rate of step 3).

    Fail happens:
        drbd_open（device->open_ro_cnt is set to non-zero）-->if condition is satisfied-->drbd_release（device->open_ro_cnt is set to zero）
    Success happends:
        drbd_open（device->open_ro_cnt is set to non-zero）-->drbd_release（device->open_ro_cnt is set to zero）-->if condition is not satisfied
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