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

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

[xuejiufei]

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?

Thanks,
--Jiufei

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

[Junxiao Bi]

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?

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

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

[xuejiufei]

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.

Thanks,
Jiufei

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

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

[Junxiao Bi]

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
>>>
>>
>>
>> .
>>
> 

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

[xuejiufei]

Hi Junxiao,
I have not describe the issue clearly.

Node 1                               Node 2(master)
dlmlock
dlm_do_master_request
                                dlm_master_request_handler
                                -> dlm_lockres_set_refmap_bit
dlmlock succeed
dlmunlock succeed

dlm_purge_lockres
                                dlm_deref_handler
                                -> find lock resource is in
                                   DLM_LOCK_RES_SETREF_INPROG state,
                                   so dispatch a deref work
dlm_purge_lockres succeed.

call dlmlock again
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

                                dlm_purge_lockres succeed

dlm_send_remote_lock_request
                                return DLM_IVLOCKID because
                                the lockres is not exist
BUG if the lockres is $RECOVERY

On 2016/1/13 10:46, Junxiao Bi wrote:
> 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
>>>>
>>>
>>>
>>> .
>>>
>>
> 
> 
> .
> 

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

[Junxiao Bi]

On 01/13/2016 02:21 PM, xuejiufei wrote:
> Hi Junxiao,
> I have not describe the issue clearly.
> 
> Node 1                               Node 2(master)
> dlmlock
> dlm_do_master_request
>                                 dlm_master_request_handler
>                                 -> dlm_lockres_set_refmap_bit
> dlmlock succeed
> dlmunlock succeed
> 
> dlm_purge_lockres
>                                 dlm_deref_handler
>                                 -> find lock resource is in
>                                    DLM_LOCK_RES_SETREF_INPROG state,
>                                    so dispatch a deref work
> dlm_purge_lockres succeed.
> 
> call dlmlock again
> 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
> 
>                                 dlm_purge_lockres succeed
> 
> dlm_send_remote_lock_request
>                                 return DLM_IVLOCKID because
>                                 the lockres is not exist
More clear now. Thank you.
This is a very complicated race. I didn't have a good solution to fix it
now. Your fix looks work, but I am afraid if we keep going fix this
kinds of races case by case, we will make dlm harder to understand and
easy to involve bugs, maybe we should think about refactor dlm.

Thanks,
Junxiao.

> BUG if the lockres is $RECOVERY
> 
> On 2016/1/13 10:46, Junxiao Bi wrote:
>> 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
>>>>>
>>>>
>>>>
>>>> .
>>>>
>>>
>>
>>
>> .
>>
> 

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

[Joseph Qi]

Hi Junxiao,

On 2016/1/13 15:00, Junxiao Bi wrote:
> On 01/13/2016 02:21 PM, xuejiufei wrote:
>> Hi Junxiao,
>> I have not describe the issue clearly.
>>
>> Node 1                               Node 2(master)
>> dlmlock
>> dlm_do_master_request
>>                                 dlm_master_request_handler
>>                                 -> dlm_lockres_set_refmap_bit
>> dlmlock succeed
>> dlmunlock succeed
>>
>> dlm_purge_lockres
>>                                 dlm_deref_handler
>>                                 -> find lock resource is in
>>                                    DLM_LOCK_RES_SETREF_INPROG state,
>>                                    so dispatch a deref work
>> dlm_purge_lockres succeed.
>>
>> call dlmlock again
>> 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
>>
>>                                 dlm_purge_lockres succeed
>>
>> dlm_send_remote_lock_request
>>                                 return DLM_IVLOCKID because
>>                                 the lockres is not exist
> More clear now. Thank you.
> This is a very complicated race. I didn't have a good solution to fix it
> now. Your fix looks work, but I am afraid if we keep going fix this
> kinds of races case by case, we will make dlm harder to understand and
> easy to involve bugs, maybe we should think about refactor dlm.
> 
Agree. IMO, the root cause is bit op cannot handle such a case.
I wonder if we have to change it to refcount, which may require a much
bigger refactoring.

Thanks,
Joseph

> Thanks,
> Junxiao.
> 
>> BUG if the lockres is $RECOVERY
>>
>> On 2016/1/13 10:46, Junxiao Bi wrote:
>>> 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
>>>>>>
>>>>>
>>>>>
>>>>> .
>>>>>
>>>>
>>>
>>>
>>> .
>>>
>>
> 
> 
> .
> 

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

[Junxiao Bi]

On 01/13/2016 04:24 PM, Joseph Qi wrote:
> Hi Junxiao,
> 
> On 2016/1/13 15:00, Junxiao Bi wrote:
>> On 01/13/2016 02:21 PM, xuejiufei wrote:
>>> Hi Junxiao,
>>> I have not describe the issue clearly.
>>>
>>> Node 1                               Node 2(master)
>>> dlmlock
>>> dlm_do_master_request
>>>                                 dlm_master_request_handler
>>>                                 -> dlm_lockres_set_refmap_bit
>>> dlmlock succeed
>>> dlmunlock succeed
>>>
>>> dlm_purge_lockres
>>>                                 dlm_deref_handler
>>>                                 -> find lock resource is in
>>>                                    DLM_LOCK_RES_SETREF_INPROG state,
>>>                                    so dispatch a deref work
>>> dlm_purge_lockres succeed.
>>>
>>> call dlmlock again
>>> 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
>>>
>>>                                 dlm_purge_lockres succeed
>>>
>>> dlm_send_remote_lock_request
>>>                                 return DLM_IVLOCKID because
>>>                                 the lockres is not exist
>> More clear now. Thank you.
>> This is a very complicated race. I didn't have a good solution to fix it
>> now. Your fix looks work, but I am afraid if we keep going fix this
>> kinds of races case by case, we will make dlm harder to understand and
>> easy to involve bugs, maybe we should think about refactor dlm.
>>
> Agree. IMO, the root cause is bit op cannot handle such a case.
> I wonder if we have to change it to refcount, which may require a much
> bigger refactoring.
one bit for each node seems reasonable, as lockres is per node. I think
the cause is the dis-order of set/clear, i am trying to see whether they
can be made happen in order.

Thanks,
Junxiao.
> 
> Thanks,
> Joseph
> 
>> Thanks,
>> Junxiao.
>>
>>> BUG if the lockres is $RECOVERY
>>>
>>> On 2016/1/13 10:46, Junxiao Bi wrote:
>>>> 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
>>>>>>>
>>>>>>
>>>>>>
>>>>>> .
>>>>>>
>>>>>
>>>>
>>>>
>>>> .
>>>>
>>>
>>
>>
>> .
>>
> 
> 

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

[xuejiufei]

On 2016/1/18 12:28, Junxiao Bi wrote:
> On 01/13/2016 04:24 PM, Joseph Qi wrote:
>> Hi Junxiao,
>>
>> On 2016/1/13 15:00, Junxiao Bi wrote:
>>> On 01/13/2016 02:21 PM, xuejiufei wrote:
>>>> Hi Junxiao,
>>>> I have not describe the issue clearly.
>>>>
>>>> Node 1                               Node 2(master)
>>>> dlmlock
>>>> dlm_do_master_request
>>>>                                 dlm_master_request_handler
>>>>                                 -> dlm_lockres_set_refmap_bit
>>>> dlmlock succeed
>>>> dlmunlock succeed
>>>>
>>>> dlm_purge_lockres
>>>>                                 dlm_deref_handler
>>>>                                 -> find lock resource is in
>>>>                                    DLM_LOCK_RES_SETREF_INPROG state,
>>>>                                    so dispatch a deref work
>>>> dlm_purge_lockres succeed.
>>>>
>>>> call dlmlock again
>>>> 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
>>>>
>>>>                                 dlm_purge_lockres succeed
>>>>
>>>> dlm_send_remote_lock_request
>>>>                                 return DLM_IVLOCKID because
>>>>                                 the lockres is not exist
>>> More clear now. Thank you.
>>> This is a very complicated race. I didn't have a good solution to fix it
>>> now. Your fix looks work, but I am afraid if we keep going fix this
>>> kinds of races case by case, we will make dlm harder to understand and
>>> easy to involve bugs, maybe we should think about refactor dlm.
>>>
>> Agree. IMO, the root cause is bit op cannot handle such a case.
>> I wonder if we have to change it to refcount, which may require a much
>> bigger refactoring.
> one bit for each node seems reasonable, as lockres is per node. I think
> the cause is the dis-order of set/clear, i am trying to see whether they
> can be made happen in order.
> 
Agree. The solution 1) in my first mail is going to add a new message to
keep the order of set and clear. Other nodes can purge the lock resource
only after the refmap on master is cleared.

Thanks
Jiufei

> Thanks,
> Junxiao.
>>
>> Thanks,
>> Joseph
>>
>>> Thanks,
>>> Junxiao.
>>>
>>>> BUG if the lockres is $RECOVERY
>>>>
>>>> On 2016/1/13 10:46, Junxiao Bi wrote:
>>>>> 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
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> .
>>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> .
>>>>>
>>>>
>>>
>>>
>>> .
>>>
>>
>>
> 
> 
> .
> 

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

[Junxiao Bi]

Hi Jiufei & Joseph,

On 01/18/2016 03:07 PM, xuejiufei wrote:
> 
> 
> On 2016/1/18 12:28, Junxiao Bi wrote:
>> On 01/13/2016 04:24 PM, Joseph Qi wrote:
>>> Hi Junxiao,
>>>
>>> On 2016/1/13 15:00, Junxiao Bi wrote:
>>>> On 01/13/2016 02:21 PM, xuejiufei wrote:
>>>>> Hi Junxiao,
>>>>> I have not describe the issue clearly.
>>>>>
>>>>> Node 1                               Node 2(master)
>>>>> dlmlock
>>>>> dlm_do_master_request
>>>>>                                 dlm_master_request_handler
>>>>>                                 -> dlm_lockres_set_refmap_bit
>>>>> dlmlock succeed
>>>>> dlmunlock succeed
>>>>>
>>>>> dlm_purge_lockres
>>>>>                                 dlm_deref_handler
>>>>>                                 -> find lock resource is in
>>>>>                                    DLM_LOCK_RES_SETREF_INPROG state,
>>>>>                                    so dispatch a deref work
>>>>> dlm_purge_lockres succeed.
>>>>>
>>>>> call dlmlock again
>>>>> 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
>>>>>
>>>>>                                 dlm_purge_lockres succeed
>>>>>
>>>>> dlm_send_remote_lock_request
>>>>>                                 return DLM_IVLOCKID because
>>>>>                                 the lockres is not exist
>>>> More clear now. Thank you.
>>>> This is a very complicated race. I didn't have a good solution to fix it
>>>> now. Your fix looks work, but I am afraid if we keep going fix this
>>>> kinds of races case by case, we will make dlm harder to understand and
>>>> easy to involve bugs, maybe we should think about refactor dlm.
>>>>
>>> Agree. IMO, the root cause is bit op cannot handle such a case.
>>> I wonder if we have to change it to refcount, which may require a much
>>> bigger refactoring.
>> one bit for each node seems reasonable, as lockres is per node. I think
>> the cause is the dis-order of set/clear, i am trying to see whether they
>> can be made happen in order.
>>
> Agree. The solution 1) in my first mail is going to add a new message to
> keep the order of set and clear. Other nodes can purge the lock resource
> only after the refmap on master is cleared.
I am taking another way, try to delete deref_lockres_worker, and make
deref refmap happen directly in deref handler. This needs find the
dis-order part and fix. As I can see, the dis-order can only happen at
do_assert_master set refmap after deref_lockres_handler clear it?

For this, need make sure not return MASTERY_REF to owner after purge.
SETREF_INPROG is designed to do this. It is set by assert_master_handler
and purge will wait it cleared before deref lockres. There are two cases
where SETREF_INPROG is not set when purge

1. assert master message not coming when purge()
This happened when lockres owner already exist when asking for a
lockres. Lockres owner will be known from master request message and
dlm_get_lock_resouces return. Soon dlmlock/dlmunlock is done, and purge
done. Then assert master message coming, but since MLE have been deleted
in dlm_get_lock_resouce, it will not return MASTERY_REF to owner to
reset refmap. So no problem in this case.

2. assert master handler set SETREF_INPROG too late
SETREF_INPROG is set after lockres owner has been updated and
dlm->spinlock released. That will make dlm_get_lock_resource waken up
too fast, and then purge may happen before SETREF_INPROG is set. This is
a bug and can be fix by the following patch.

diff --git a/fs/ocfs2/dlm/dlmmaster.c b/fs/ocfs2/dlm/dlmmaster.c
index 9477d6e1de37..83cd65b128d0 100644
--- a/fs/ocfs2/dlm/dlmmaster.c
+++ b/fs/ocfs2/dlm/dlmmaster.c
@@ -1965,6 +1965,7 @@ ok:
                if (res) {
                        int wake = 0;
                        spin_lock(&res->spinlock);
+                       res->state |= DLM_LOCK_RES_SETREF_INPROG;
                        if (mle->type == DLM_MLE_MIGRATION) {
                                mlog(0, "finishing off migration of
lockres %.*s, "
                                        "from %u to %u\n",
@@ -2029,12 +2030,8 @@ ok:

 done:
        ret = 0;
-       if (res) {
-               spin_lock(&res->spinlock);
-               res->state |= DLM_LOCK_RES_SETREF_INPROG;
-               spin_unlock(&res->spinlock);
+       if (res)
                *ret_data = (void *)res;
-       }
        dlm_put(dlm);
        if (master_request) {
                mlog(0, "need to tell master to reassert\n");


Besides this path, revert commit
f3f854648de64c4b6f13f6f13113bc9525c621e5 ("ocfs2_dlm: Ensure correct
ordering of set/clear refmap bit on lockres"), can this fix this issue?

Thanks,
Junxiao.



> 
> Thanks
> Jiufei
> 
>> Thanks,
>> Junxiao.
>>>
>>> Thanks,
>>> Joseph
>>>
>>>> Thanks,
>>>> Junxiao.
>>>>
>>>>> BUG if the lockres is $RECOVERY
>>>>>
>>>>> On 2016/1/13 10:46, Junxiao Bi wrote:
>>>>>> 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
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> .
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>> .
>>>>>>
>>>>>
>>>>
>>>>
>>>> .
>>>>
>>>
>>>
>>
>>
>> .
>>
> 

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

[xuejiufei]

Hi Junxiao,
commit f3f854648de64c4b6f13f6f13113bc9525c621e5 is to solve
the disorder problem of set/clear refmap on master.
If it is reverted, how to fix the problem the patch
described?

I think the following is the issue that patch fixed.
The set refmap bit message is sent before the clear refmap
message. But these two message is processed by different
processes, so the set refmap message may be handled before the clear.

Node 1                                    Node 2(master)
                               dlm_wq                  o2net_wq
                           dlm_do_assert_master
dlm_do_assert_handler
return MASTERY_REF
                           receive MASTERY_REF
dlm_purge_lockres
send deref message
                                           receive deref message
                                           -> dlm_deref_lockres_handler
                                              and clear refmap
                           -> set refmap

On 2016/1/19 11:03, Junxiao Bi wrote:
> Hi Jiufei & Joseph,
> 
> On 01/18/2016 03:07 PM, xuejiufei wrote:
>>
>>
>> On 2016/1/18 12:28, Junxiao Bi wrote:
>>> On 01/13/2016 04:24 PM, Joseph Qi wrote:
>>>> Hi Junxiao,
>>>>
>>>> On 2016/1/13 15:00, Junxiao Bi wrote:
>>>>> On 01/13/2016 02:21 PM, xuejiufei wrote:
>>>>>> Hi Junxiao,
>>>>>> I have not describe the issue clearly.
>>>>>>
>>>>>> Node 1                               Node 2(master)
>>>>>> dlmlock
>>>>>> dlm_do_master_request
>>>>>>                                 dlm_master_request_handler
>>>>>>                                 -> dlm_lockres_set_refmap_bit
>>>>>> dlmlock succeed
>>>>>> dlmunlock succeed
>>>>>>
>>>>>> dlm_purge_lockres
>>>>>>                                 dlm_deref_handler
>>>>>>                                 -> find lock resource is in
>>>>>>                                    DLM_LOCK_RES_SETREF_INPROG state,
>>>>>>                                    so dispatch a deref work
>>>>>> dlm_purge_lockres succeed.
>>>>>>
>>>>>> call dlmlock again
>>>>>> 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
>>>>>>
>>>>>>                                 dlm_purge_lockres succeed
>>>>>>
>>>>>> dlm_send_remote_lock_request
>>>>>>                                 return DLM_IVLOCKID because
>>>>>>                                 the lockres is not exist
>>>>> More clear now. Thank you.
>>>>> This is a very complicated race. I didn't have a good solution to fix it
>>>>> now. Your fix looks work, but I am afraid if we keep going fix this
>>>>> kinds of races case by case, we will make dlm harder to understand and
>>>>> easy to involve bugs, maybe we should think about refactor dlm.
>>>>>
>>>> Agree. IMO, the root cause is bit op cannot handle such a case.
>>>> I wonder if we have to change it to refcount, which may require a much
>>>> bigger refactoring.
>>> one bit for each node seems reasonable, as lockres is per node. I think
>>> the cause is the dis-order of set/clear, i am trying to see whether they
>>> can be made happen in order.
>>>
>> Agree. The solution 1) in my first mail is going to add a new message to
>> keep the order of set and clear. Other nodes can purge the lock resource
>> only after the refmap on master is cleared.
> I am taking another way, try to delete deref_lockres_worker, and make
> deref refmap happen directly in deref handler. This needs find the
> dis-order part and fix. As I can see, the dis-order can only happen at
> do_assert_master set refmap after deref_lockres_handler clear it?
> 
> For this, need make sure not return MASTERY_REF to owner after purge.
> SETREF_INPROG is designed to do this. It is set by assert_master_handler
> and purge will wait it cleared before deref lockres. There are two cases
> where SETREF_INPROG is not set when purge
> 
> 1. assert master message not coming when purge()
> This happened when lockres owner already exist when asking for a
> lockres. Lockres owner will be known from master request message and
> dlm_get_lock_resouces return. Soon dlmlock/dlmunlock is done, and purge
> done. Then assert master message coming, but since MLE have been deleted
> in dlm_get_lock_resouce, it will not return MASTERY_REF to owner to
> reset refmap. So no problem in this case.
> 
> 2. assert master handler set SETREF_INPROG too late
> SETREF_INPROG is set after lockres owner has been updated and
> dlm->spinlock released. That will make dlm_get_lock_resource waken up
> too fast, and then purge may happen before SETREF_INPROG is set. This is
> a bug and can be fix by the following patch.
> 
> diff --git a/fs/ocfs2/dlm/dlmmaster.c b/fs/ocfs2/dlm/dlmmaster.c
> index 9477d6e1de37..83cd65b128d0 100644
> --- a/fs/ocfs2/dlm/dlmmaster.c
> +++ b/fs/ocfs2/dlm/dlmmaster.c
> @@ -1965,6 +1965,7 @@ ok:
>                 if (res) {
>                         int wake = 0;
>                         spin_lock(&res->spinlock);
> +                       res->state |= DLM_LOCK_RES_SETREF_INPROG;
>                         if (mle->type == DLM_MLE_MIGRATION) {
>                                 mlog(0, "finishing off migration of
> lockres %.*s, "
>                                         "from %u to %u\n",
> @@ -2029,12 +2030,8 @@ ok:
> 
>  done:
>         ret = 0;
> -       if (res) {
> -               spin_lock(&res->spinlock);
> -               res->state |= DLM_LOCK_RES_SETREF_INPROG;
> -               spin_unlock(&res->spinlock);
> +       if (res)
>                 *ret_data = (void *)res;
> -       }
>         dlm_put(dlm);
>         if (master_request) {
>                 mlog(0, "need to tell master to reassert\n");
> 
> 
> Besides this path, revert commit
> f3f854648de64c4b6f13f6f13113bc9525c621e5 ("ocfs2_dlm: Ensure correct
> ordering of set/clear refmap bit on lockres"), can this fix this issue?
> 
> Thanks,
> Junxiao.
> 
> 
> 
>>
>> Thanks
>> Jiufei
>>
>>> Thanks,
>>> Junxiao.
>>>>
>>>> Thanks,
>>>> Joseph
>>>>
>>>>> Thanks,
>>>>> Junxiao.
>>>>>
>>>>>> BUG if the lockres is $RECOVERY
>>>>>>
>>>>>> On 2016/1/13 10:46, Junxiao Bi wrote:
>>>>>>> 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
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> .
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> .
>>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> .
>>>>>
>>>>
>>>>
>>>
>>>
>>> .
>>>
>>
> 
> 
> .
> 

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

[Junxiao Bi]

Hi Jiufei,

Right. Revert that patch will introduce that dis-order, thank you for
pointing it out. I will think about more about it. My idea is to do some
refactor to make it more smooth while not introducing complicated things
to just fix that bug.

Thanks,
Junxiao.
On 01/19/2016 04:19 PM, xuejiufei wrote:
> Hi Junxiao,
> commit f3f854648de64c4b6f13f6f13113bc9525c621e5 is to solve
> the disorder problem of set/clear refmap on master.
> If it is reverted, how to fix the problem the patch
> described?

> 
> I think the following is the issue that patch fixed.
> The set refmap bit message is sent before the clear refmap
> message. But these two message is processed by different
> processes, so the set refmap message may be handled before the clear.
> 
> Node 1                                    Node 2(master)
>                                dlm_wq                  o2net_wq
>                            dlm_do_assert_master
> dlm_do_assert_handler
> return MASTERY_REF
>                            receive MASTERY_REF
> dlm_purge_lockres
> send deref message
>                                            receive deref message
>                                            -> dlm_deref_lockres_handler
>                                               and clear refmap
>                            -> set refmap
> 
> On 2016/1/19 11:03, Junxiao Bi wrote:
>> Hi Jiufei & Joseph,
>>
>> On 01/18/2016 03:07 PM, xuejiufei wrote:
>>>
>>>
>>> On 2016/1/18 12:28, Junxiao Bi wrote:
>>>> On 01/13/2016 04:24 PM, Joseph Qi wrote:
>>>>> Hi Junxiao,
>>>>>
>>>>> On 2016/1/13 15:00, Junxiao Bi wrote:
>>>>>> On 01/13/2016 02:21 PM, xuejiufei wrote:
>>>>>>> Hi Junxiao,
>>>>>>> I have not describe the issue clearly.
>>>>>>>
>>>>>>> Node 1                               Node 2(master)
>>>>>>> dlmlock
>>>>>>> dlm_do_master_request
>>>>>>>                                 dlm_master_request_handler
>>>>>>>                                 -> dlm_lockres_set_refmap_bit
>>>>>>> dlmlock succeed
>>>>>>> dlmunlock succeed
>>>>>>>
>>>>>>> dlm_purge_lockres
>>>>>>>                                 dlm_deref_handler
>>>>>>>                                 -> find lock resource is in
>>>>>>>                                    DLM_LOCK_RES_SETREF_INPROG state,
>>>>>>>                                    so dispatch a deref work
>>>>>>> dlm_purge_lockres succeed.
>>>>>>>
>>>>>>> call dlmlock again
>>>>>>> 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
>>>>>>>
>>>>>>>                                 dlm_purge_lockres succeed
>>>>>>>
>>>>>>> dlm_send_remote_lock_request
>>>>>>>                                 return DLM_IVLOCKID because
>>>>>>>                                 the lockres is not exist
>>>>>> More clear now. Thank you.
>>>>>> This is a very complicated race. I didn't have a good solution to fix it
>>>>>> now. Your fix looks work, but I am afraid if we keep going fix this
>>>>>> kinds of races case by case, we will make dlm harder to understand and
>>>>>> easy to involve bugs, maybe we should think about refactor dlm.
>>>>>>
>>>>> Agree. IMO, the root cause is bit op cannot handle such a case.
>>>>> I wonder if we have to change it to refcount, which may require a much
>>>>> bigger refactoring.
>>>> one bit for each node seems reasonable, as lockres is per node. I think
>>>> the cause is the dis-order of set/clear, i am trying to see whether they
>>>> can be made happen in order.
>>>>
>>> Agree. The solution 1) in my first mail is going to add a new message to
>>> keep the order of set and clear. Other nodes can purge the lock resource
>>> only after the refmap on master is cleared.
>> I am taking another way, try to delete deref_lockres_worker, and make
>> deref refmap happen directly in deref handler. This needs find the
>> dis-order part and fix. As I can see, the dis-order can only happen at
>> do_assert_master set refmap after deref_lockres_handler clear it?
>>
>> For this, need make sure not return MASTERY_REF to owner after purge.
>> SETREF_INPROG is designed to do this. It is set by assert_master_handler
>> and purge will wait it cleared before deref lockres. There are two cases
>> where SETREF_INPROG is not set when purge
>>
>> 1. assert master message not coming when purge()
>> This happened when lockres owner already exist when asking for a
>> lockres. Lockres owner will be known from master request message and
>> dlm_get_lock_resouces return. Soon dlmlock/dlmunlock is done, and purge
>> done. Then assert master message coming, but since MLE have been deleted
>> in dlm_get_lock_resouce, it will not return MASTERY_REF to owner to
>> reset refmap. So no problem in this case.
>>
>> 2. assert master handler set SETREF_INPROG too late
>> SETREF_INPROG is set after lockres owner has been updated and
>> dlm->spinlock released. That will make dlm_get_lock_resource waken up
>> too fast, and then purge may happen before SETREF_INPROG is set. This is
>> a bug and can be fix by the following patch.
>>
>> diff --git a/fs/ocfs2/dlm/dlmmaster.c b/fs/ocfs2/dlm/dlmmaster.c
>> index 9477d6e1de37..83cd65b128d0 100644
>> --- a/fs/ocfs2/dlm/dlmmaster.c
>> +++ b/fs/ocfs2/dlm/dlmmaster.c
>> @@ -1965,6 +1965,7 @@ ok:
>>                 if (res) {
>>                         int wake = 0;
>>                         spin_lock(&res->spinlock);
>> +                       res->state |= DLM_LOCK_RES_SETREF_INPROG;
>>                         if (mle->type == DLM_MLE_MIGRATION) {
>>                                 mlog(0, "finishing off migration of
>> lockres %.*s, "
>>                                         "from %u to %u\n",
>> @@ -2029,12 +2030,8 @@ ok:
>>
>>  done:
>>         ret = 0;
>> -       if (res) {
>> -               spin_lock(&res->spinlock);
>> -               res->state |= DLM_LOCK_RES_SETREF_INPROG;
>> -               spin_unlock(&res->spinlock);
>> +       if (res)
>>                 *ret_data = (void *)res;
>> -       }
>>         dlm_put(dlm);
>>         if (master_request) {
>>                 mlog(0, "need to tell master to reassert\n");
>>
>>
>> Besides this path, revert commit
>> f3f854648de64c4b6f13f6f13113bc9525c621e5 ("ocfs2_dlm: Ensure correct
>> ordering of set/clear refmap bit on lockres"), can this fix this issue?
>>
>> Thanks,
>> Junxiao.
>>
>>
>>
>>>
>>> Thanks
>>> Jiufei
>>>
>>>> Thanks,
>>>> Junxiao.
>>>>>
>>>>> Thanks,
>>>>> Joseph
>>>>>
>>>>>> Thanks,
>>>>>> Junxiao.
>>>>>>
>>>>>>> BUG if the lockres is $RECOVERY
>>>>>>>
>>>>>>> On 2016/1/13 10:46, Junxiao Bi wrote:
>>>>>>>> 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
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> .
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> .
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>> .
>>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>> .
>>>>
>>>
>>
>>
>> .
>>
> 

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

[Junxiao Bi]

Hi Jiufei,

I didn't find other solution for this issue. You can go with yours.
Looks like your second one is more straightforward, there deref work can
be removed.

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

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

[xuejiufei]

Hi Junxiao,

On 2016/1/21 15:34, Junxiao Bi wrote:
> Hi Jiufei,
> 
> I didn't find other solution for this issue. You can go with yours.
> Looks like your second one is more straightforward, there deref work can
> be removed.
> 
There are two problems with the second solution:
1) Node retry to deref the lock resource will block dlm_thread to process
other lock resources.
2) When node retries to drop the refmap bit, the master may be in another
assert master work, that will take a long time to purge a lockres.
So I prefer the first solution.

Thanks,
Jiufei

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

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

[Junxiao Bi]

On 01/26/2016 09:43 AM, xuejiufei wrote:
> Hi Junxiao,
> 
> On 2016/1/21 15:34, Junxiao Bi wrote:
>> Hi Jiufei,
>>
>> I didn't find other solution for this issue. You can go with yours.
>> Looks like your second one is more straightforward, there deref work can
>> be removed.
>>
> There are two problems with the second solution:
> 1) Node retry to deref the lock resource will block dlm_thread to process
> other lock resources.
Yes, a little, but i don't think that will be long. Indeed I think about
clear DLM_LOCK_RES_DROPPING_REF and requeue lockres again before, that
will not block dlm_thread, but I found dlm had an assuming about this
flag, it assumed the lockres is gone if it is set. If this bad assuming
can be fixed, the second solution will be much better.

> 2) When node retries to drop the refmap bit, the master may be in another
> assert master work, that will take a long time to purge a lockres.
Delay purging lockres maybe not a bad idea, but a good one. Like in your
case, the second lock request can go directly without master reqeust.
This can improve performance.

Thanks,
Junxiao.

> So I prefer the first solution.
> 
> Thanks,
> Jiufei
> 
>> Thanks,
>> Junxiao.
>> 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?
>>>
>>> Thanks,
>>> --Jiufei
>>>
>>
>>
>> .
>>
>