From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wengang Wang Date: Thu, 13 Oct 2011 10:13:56 +0800 Subject: [Ocfs2-devel] avoid being purged when queued for assert_master In-Reply-To: <4E9648E1.3070508@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> Message-ID: <20111013021356.GD5565@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 11-10-12 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 >