[Ocfs2-devel] ocfs2: A race between refmap setting and clearing

[Junxiao Bi <junxiao.bi@oracle.com>]

On 01/12/2016 03:16 PM, xuejiufei wrote:
> Hi, Junxiao
> 
> On 2016/1/12 12:03, Junxiao Bi wrote:
>> Hi Jiufei,
>>
>> On 01/11/2016 10:46 AM, xuejiufei wrote:
>>> Hi all,
>>> We have found a race between refmap setting and clearing which
>>> will cause the lock resource on master is freed before other nodes
>>> purge it.
>>>
>>> Node 1                               Node 2(master)
>>> dlm_do_master_request
>>>                                 dlm_master_request_handler
>>>                                 -> dlm_lockres_set_refmap_bit
>>> call dlm_purge_lockres after unlock
>>>                                 dlm_deref_handler
>>>                                 -> find lock resource is in
>>>                                    DLM_LOCK_RES_SETREF_INPROG state,
>>>                                    so dispatch a deref work
>>> dlm_purge_lockres succeed.
>>>
>>> dlm_do_master_request
>>>                                 dlm_master_request_handler
>>>                                 -> dlm_lockres_set_refmap_bit
>>>
>>>                                 deref work trigger, call
>>>                                 dlm_lockres_clear_refmap_bit
>>>                                 to clear Node 1 from refmap
>>>
>>> Now Node 2 can purge the lock resource but the owner of lock resource
>>> on Node 1 is still Node 2 which may trigger BUG if the lock resource
>>> is $RECOVERY or other problems.
>>>
>>> We have discussed 2 solutions:
>>> 1)The master return error to Node 1 if the DLM_LOCK_RES_SETREF_INPROG
>>> is set. Node 1 will not retry and master send another message to Node 1
>>> after clearing the refmap. Node 1 can purge the lock resource after the
>>> refmap on master is cleared.
>>> 2) The master return error to Node 1 if the DLM_LOCK_RES_SETREF_INPROG
>>> is set, and Node 1 will retry to deref the lockres.
>>>
>>> Does anybody has better ideas?
>>>
>> dlm_purge_lockres() will wait to drop ref until
>> DLM_LOCK_RES_SETREF_INPROG cleared. So if set this flag when find the
>> master during doing master request. And then this flag was cleared when
>> receiving assert master message, can this fix the issue?
>>
> I don't think this can fix. Before doing master request, the lock resource is
> already purged. The master should clear the refmap before client purge it.
inflight_locks is increased in dlm_get_lock_resource() which will stop
lockres purged? Set DLM_LOCK_RES_SETREF_INPROG when found lockres owner
during master request, then this will stop lockres purged after unlock?

Thanks,
Junxiao.

> 
> Thanks,
> Jiufei
> 
>> Thanks,
>> Junxiao.
>>> Thanks,
>>> --Jiufei
>>>
>>
>>
>> .
>>
>