[Cluster-devel] About dlm_unlock (kernel space)

[Guoqing Jiang]

On 06/13/2016 10:56 PM, David Teigland wrote:
> On Mon, Jun 13, 2016 at 07:15:09AM -0400, Guoqing Jiang wrote:
>> Hi,
>>
>> In case we have set DLM_LKF_CONVERT flag for dlm_lock, is it
>> possible that the convert
>> queue could be NULL or not NULL while perform unlock? I think there
>> are two different
>> cases would appear when call dlm_unlock:
>>
>> 1. the lock logic is in convert stage.
>> 2. convert queue is null.
>>
>> For 1, seems need to cancel the lock request first
>> (dlm_unlock+CANCEL), then call
>> dlm_unlock. And just need to call dlm_unlock directly for case 2.
>> Please correct me
>> if I am wrong.
>>
>> And what could happen if cancel a lock which has a empty convert
>> queue? Like call
>> dlm_unlock+CANCEL for case 2, is something wrong could happen?
>>
>> The last question, is there a dlm_unlock_* variant which could do
>> unlock finally for
>> both case1 and case2 (or does the variant make sense)?
> Convert is not a stable state, which means that cancel always involves a
> race:  the convert could complete before the cancel is processed.  After
> convert has finished, or after cancel has finished, then you know that the
> lock is not converting and a simple unlock will work.  I suggest you test
> these combinations to see how they behave in practice.  Doing unlock with
> FORCEUNLOCK is also an option (that works even if the lock is on the
> waiting or convert queue.)  I'd be judicious about using either CANCEL or
> FORCEUNLOCK.
>
>

Thanks a lot for detailed infos and suggestions! Looks FORCEUNLOCK
flag is perfect since it is suitable for both 1 and 2, I will use it and see
what will happen in practice.

Cheers,
Guoqing