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

[Junxiao Bi]

On 09/23/2015 09:47 AM, Joseph Qi wrote:
> On 2015/9/23 9:25, Junxiao Bi wrote:
>> On 09/22/2015 08:23 PM, Joseph Qi wrote:
>>> Hi Junxiao,
>>>
>>> On 2015/9/22 8:55, Junxiao Bi wrote:
>>>> 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?
>>>
>>> I want to keep the original logic. And for fixing the race case I
>>> described, how about the following idea?
>>>
>>> Check the status DLM_NORMAL. If res->state is currently
>>> DLM_LOCK_RES_RECOVERING (set in dlm_move_lockres_to_recovery_list, means
>>> still in recovery) or res master changed (means new master has finished
>>> the recovery), reset the status to DLM_RECOVERING, just like the check
>>> at the beginning of dlmconvert_remote. Then it is now in grant list and
>>> outer will retry.
>> How this idea fix the race windows you described in patch log? Lock is
>> reverted to granted list but dlm_send_remote_convert_request() return
>> DLM_NORMAL.
>>
> As I described in the former mail, status is now reset to DLM_RECOVERING,
> caller will retry. And the original way will just wait forever.
I mean convert request was sent to res master successfully,
dlm_send_remote_convert_request() have return DLM_NORMAL, but before res
master send ast it panic. Looks convert will not retry in this case.

Thanks,
Junxiao.
> 
> Thanks
> Joseph
> 
>> Thanks,
>> Junxiao.
>>>
>>>>
>>>> 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.
>>>>>
>>>>>
>>>>
>>>>
>>>> .
>>>>
>>>
>>>
>>
>>
>> .
>>
> 
>