[Ocfs2-devel] [PATCH] ocfs2/dlm: return DLM_CANCELGRANT if the lock is on granted list and the operation is canceled

[Changwei Ge]

Hi jun
Good afternoon.

>>>> If AST doesn't manage to get back to requested node, why must flag OCFS2_LOCK_BUSY be cleared in o2dlm_unlock_ast_wrapper?
>>>>
>>>> Yes, OCFS2_LOCK_BUSY can be cleared it either o2dlm_unlock_ast_wrapper() or o2dlm_lock_ast_wrapper() with o2cb stack applied.
>>>>
>>>> If we return DLM_CANCELGRANT from ocfs2/dlm to dlm, then we must know that AST has ever come back or master node has moved the lock to grant list itself, thus we clear flag OCFS2_LOCK_BUSY in o2dlm_lock_ast_wrapper().
>>>> Otherwise we ascertain that we can stop current ongoing locking procedure and must clear OCFS2_LOCK_BUSY in o2dlm_unlock_ast_wrapper() (*synchronized*).
>>>>
>>>> Let's summarize this, OCFS2_LOCK_BUSY should be cleared whether by locking success or cancellation success.
>>>>
>>>> And my way already check if the lock is granted then return DLM_CANCELGRANT or not.
>>>>
>>>
>>> OCFS2_LOCK_BUSY won't be cleared if DLM_CANCELGRANT is set in
>>> o2dlm_unlock_ast_wrapper, and that's what I'm concerned about:
>>
>> But we already *ascertain* that previous locking request has been *granted* before deciding to return DLM_CANCELGRANT during cancellation to o2dlm_unlock_ast_wrapper().
>>
>> If above condition stands, o2dlm_lock_ast_wrapper() must will be or have been called, which also clears OCFS2_LOCK_BUSY.
>>
> 
> 1. Node1 already has PR lock, and wants to get ex.
Well, a locking up-conversion procedure.

> 2. Node1 receive BAST and do unlock, here OCFS2_LOCK_BUSY is set.
Because there are two concurrent up-conversion, which conflict, so one of them must be canceled!

> 3. Node1 can not receive the AST for unlock as master dead.
So here you mean the lock can't be granted.

> 4. Then o2dlm_unlock_ast_wrapper will be called rather than o2dlm_lock_ast_wrapper.
Then the cancellation succeeds as the master dies.

> 5. Actually the *granted* lock request has nothing to do with OCFS2_LOCK_BUSY.
Yes, o2dlm_lock_ast_wrapper will not clear OCFS2_LOCK_BUSY.

But my suggestion was not against above timing sequence.
Did you misunderstand my suggestion?
And the original logic of Jian's patch also returns DLM_CANCELGRANT.

Thanks,
Changwei