From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sunil Mushran Date: Wed, 12 Oct 2011 19:11:45 -0700 Subject: [Ocfs2-devel] avoid being purged when queued for assert_master In-Reply-To: <20111013020712.GB5565@laptop.jp.oracle.com> References: <20111012070433.GA11852@laptop.jp.oracle.com> <4E963190.1080803@oracle.com> <20111013010229.GA3680@laptop.jp.oracle.com> <4E964332.1020201@oracle.com> <20111013015137.GA5565@laptop.jp.oracle.com> <20111013020712.GB5565@laptop.jp.oracle.com> Message-ID: <4E9648E1.3070508@oracle.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: ocfs2-devel@oss.oracle.com That's what ovm does. Have you reproduced it with ovm3 kernel? On 10/12/2011 07:07 PM, Wengang Wang wrote: > On 11-10-13 09:51, Wengang Wang wrote: >> On 11-10-12 18:47, Sunil Mushran wrote: >>> I meant master_request (not query). We set refmap _before_ >>> asserting. So that should not happen. >> Why can't the remote node requested deref (DLM_DEREF_LOCKRES_MSG)? > The problem can easily happen on this dlmfs useage: > > reopen: > open(create) /dlm/dirxx/filexx > close /dlm/dirxx/filexx > sleep 60 > goto reopen > >> thanks, >> wengang. >>> On 10/12/2011 06:02 PM, Wengang Wang wrote: >>>> Hi Sunil, >>>> >>>> On 11-10-12 17:32, Sunil Mushran wrote: >>>>> So you are saying a lockres can get purged before the node is asserting >>>>> master to other nodes? >>>>> >>>>> The main place where we dispatch assert is during master_query. >>>>> There we set refmap before dispatching. Meaning refmap will protect >>>>> us from purging. >>>>> >>>>> But I think it could happen in master_requery, which only comes into >>>>> play if a node dies during migration. >>>>> >>>>> Is that the case here? >>>> I think this can mainly include the response for a master_request. >>>> in dlm_master_request_handler(), the master node quques assert_master. >>>> The node which requested a master_request knows the master by receving >>>> response values. It doesn't need to wait until the assert_master come. >>>> As you know, the asserting master work is done in a workqueue. And the >>>> work item in it can be heavily delayed. So in the duriation from the >>>> (old) master responding with "Yes, I am master" to it sending assert_master, >>>> Anything can heppan, the worse case is the lockres on the (old) master >>>> get purged and is remasted by another node. So in this case, >>>> apparently, the old master shouldn't send the assert_master any longer. >>>> To prevent that from happening, we should keep the lockres un-purged as >>>> long as it's queued for master_request. >>>> >>>> #the problem is what my flush_workqueue patch tries to fix. >>>> >>>> thanks, >>>> wengang. >>>> >>>>> On 10/12/2011 12:04 AM, Wengang Wang wrote: >>>>>> Hi Sunil/Joel/Mark and anyone who has interest, >>>>>> >>>>>> This is not a patch but a discuss. >>>>>> >>>>>> Currently we have a problem: >>>>>> When a lockres is still queued(in dlm->work_list) for sending an >>>>>> assert_master(or in processing of sending), the lockres can't be >>>>>> purged(removed from hash). there is no flag/state,on lockres its self,dinotes >>>>>> this situation. >>>>>> >>>>>> The badness is that if the lockres is purged(surely not the owner at the >>>>>> moment), and the assert_master is after the purge. it can confuse other >>>>>> nodes. On another node, the owner now can be any other nodes, thus on >>>>>> receiving the assert_master, it can trigger a BUG() because 'owner' >>>>>> doesn't match. >>>>>> >>>>>> So we'd better to prevent the lockres from be purged when it's queued >>>>>> for something(assert_master). >>>>>> >>>>>> Srini and I discussed some possible fixes: >>>>>> 1) adding a flag to lockres->state. >>>>>> this does not work. A lockres can have multiple instances in the queue list. >>>>>> A simple flag is not safe. And the instances are not nested, so even >>>>>> saving a previous flags doesn't work. Neither can we merge the instances >>>>>> because they can be for different purposes. >>>>>> >>>>>> 2) checking if the lockres if queued before purging it. >>>>>> this works, but doesn't sounds good. it needs changes of current behaviour >>>>>> on the queue list. Also, we have no idea on the performance of the checking >>>>>> (searching list). >>>>>> >>>>>> 3) making use of lockres->inflight_locks. >>>>>> this works, but seems to be a mis-use of inflight_locks. >>>>>> >>>>>> 4) adding a new member to lockres counting the queued time. >>>>>> this works and simple. but needs extra memory. >>>>>> >>>>>> I prefer to the 4). >>>>>> >>>>>> What's your idea? >>>>>> >>>>>> thanks, >>>>>> wengang. >>>>>> >>>>>> _______________________________________________ >>>>>> Ocfs2-devel mailing list >>>>>> Ocfs2-devel at oss.oracle.com >>>>>> http://oss.oracle.com/mailman/listinfo/ocfs2-devel