From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wengang Wang Date: Fri, 14 Oct 2011 07:35:49 +0800 Subject: [Ocfs2-devel] avoid being purged when queued for assert_master In-Reply-To: <4E970D2E.2080206@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> <4E9648E1.3070508@oracle.com> <20111013021356.GD5565@laptop.jp.oracle.com> <4E970D2E.2080206@oracle.com> Message-ID: <20111013233549.GA2982@laptop.jp.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 On 11-10-13 09:09, Sunil Mushran wrote: > The last email you said it reproduced. Now you say it did not. > I'm confused. Oh? Did I. If I did, I meant it had reproductions in different customers's ENV, I had no reproduction in house. Sorry for confusion :P thanks, wengang. > > On 10/12/2011 07:13 PM, Wengang Wang wrote: > >On 11-10-12 19:11, Sunil Mushran wrote: > >>That's what ovm does. Have you reproduced it with ovm3 kernel? > >> > >No, I have no reproductions. > > > >thanks, > >wengang. > >>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 >