[Ocfs2-devel] [PATCH v2] ocfs2/dlm: fix race between convert and recovery

[Junxiao Bi]

On 09/21/2015 05:23 PM, Joseph Qi wrote:
> Hi Junxiao,
> This solution may have problem in the following scenario:
> Consider dlm_send_remote_convert_request has taken too much time, and
> dlm_move_lockres_to_recovery_list runs first and new master will see
> this node is currently in convert list after recovery.
> Then dlm_send_remote_convert_request returns other than DLM_NORMAL and
> it will revert it to grant list, then retry convert. This will makes
> this node and master inconsistent.
> I will try to find another solution to resolve the race issue.

If master is down, no need retry convert. May check the return value of
dlm_send_remote_convert_request(), if DLM_RECOVERING, don't retry,
otherwise retry?

Thanks,
Junxiao.

> 
> On 2015/9/20 15:20, Junxiao Bi wrote:
>> Reviewed-by: Junxiao Bi <junxiao.bi at oracle.com>
>>
>>>> 在 2015年9月18日，下午7:25，Joseph Qi <joseph.qi at huawei.com> 写道：
>>>>
>>>> There is a race window between dlmconvert_remote and
>>>> dlm_move_lockres_to_recovery_list, which will cause a lock with
>>>> OCFS2_LOCK_BUSY in grant list, thus system hangs.
>>>>
>>>> dlmconvert_remote
>>>> {
>>>>        spin_lock(&res->spinlock);
>>>>        list_move_tail(&lock->list, &res->converting);
>>>>        lock->convert_pending = 1;
>>>>        spin_unlock(&res->spinlock);
>>>>
>>>>        status = dlm_send_remote_convert_request();
>>>>>>>>>>>>>>>> race window, master has queued ast and return DLM_NORMAL,
>>>>               and then down before sending ast.
>>>>               this node detects master down and calls
>>>>               dlm_move_lockres_to_recovery_list, which will revert the
>>>>               lock to grant list.
>>>>               Then OCFS2_LOCK_BUSY won't be cleared as new master won't
>>>>               send ast any more because it thinks already be authorized.
>>>>
>>>>        spin_lock(&res->spinlock);
>>>>        lock->convert_pending = 0;
>>>>        if (status != DLM_NORMAL)
>>>>                dlm_revert_pending_convert(res, lock);
>>>>        spin_unlock(&res->spinlock);
>>>> }
>>>>
>>>> In this case, just leave it in convert list and new master will take care
>>>> of it after recovery.  And if convert request returns other than
>>>> DLM_NORMAL, convert thread will do the revert itself. So remove the
>>>> revert logic in dlm_move_lockres_to_recovery_list.
>>>>
>>>> changelog since v1:
>>>> Clean up convert_pending since it is now useless.
> 
>