Re: [PATCH 06/12] md-cluster: add the error check if failed to get dlm lock

[Guoqing Jiang <gqJiang@suse.com>]

NeilBrown wrote:
> On Tue, 28 Jul 2015 11:04:31 +0800 Guoqing Jiang <gqJiang@suse.com>
> wrote:
>
>   
>> Hi Goldwyn,
>>
>> Goldwyn Rodrigues wrote:
>>     
>>> Hi Guoqing,
>>>
>>> On 07/10/2015 04:01 AM, Guoqing Jiang wrote:
>>>       
>>>> In complicated cluster environment, it is possible that the
>>>> dlm lock couldn't be get/convert on purpose, the related err
>>>> info is added for better debug potential issue.
>>>>
>>>> For lockres_free, if the lock is blocking by a lock request or
>>>> conversion request, then dlm_unlock just put it back to grant
>>>> queue, so need to ensure the lock is free finally.
>>>>         
>>> I cannot think of a scenario where a DLM_CANCEL will be returned.
>>> Could you explain the situation a bit more?
>>>
>>>       
>> Thanks for the review. When the node is receiving message where it needs
>> to convert message
>> lock, and lockres_free is invoked if user stop array meanwhile, then the
>> message lock is put back
>> to grant queue at the CR mode and message lock is not released, am I
>> misunderstood the case?
>>
>> Thanks,
>> Guoqing
>>     
>
> Thanks for these patches Guoqing and for the review Goldwyn.
>
> I've queued all but the last one (which you both agree we don't need).
>
> I have queued this one too for now, though it Goldwyn has further
> comments I'd be very happy to see them.
>
> I'm a bit bothered by:
> +retry:
> +	ret = dlm_unlock(res->ls, res->lksb.sb_lkid, 0, &res->lksb, res);
> +	if (unlikely(ret != 0)) {
> +		pr_info("%s: failed to unlock %s return %d\n", __func__, res->name, ret);
> +
> +		/* if a lock conversion is cancelled, then the lock is put
> +		 * back to grant queue, need to ensure it is unlocked */
> +		if (ret == -DLM_ECANCEL)
> +			goto retry;
> +	}
>
> which looks like it could loop repeatedly.  Maybe if there was
> documentation for DLM_LKF_CANCEL or DLM_ECANCEL somewhere, that might
> make me feel more comfortable, but the only documentation that I can
> find is the code ... is there real documentation that google doesn't
> find for me?
>
>   
Hi Neil,

Please see the people.redhat.com/ccaulfie/docs/rhdlmbook.pdf, I guess it
is the only
official book about DLM. And for the above code, I am mostly referred to
page 37-38
which described dlm_unlock API.

BTW: do you have time to review the following other three patches for
mdadm? Thanks.
    http://www.spinics.net/lists/raid/msg49356.html
    http://www.spinics.net/lists/raid/msg49357.html
    http://www.spinics.net/lists/raid/msg49358.html

Best Regards,
Guoqing