From mboxrd@z Thu Jan 1 00:00:00 1970 From: xuejiufei Date: Tue, 12 Jan 2016 15:16:39 +0800 Subject: [Ocfs2-devel] ocfs2: A race between refmap setting and clearing In-Reply-To: <56947B02.7030503@oracle.com> References: <56931785.2090603@huawei.com> <56947B02.7030503@oracle.com> Message-ID: <5694A857.5020906@huawei.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: ocfs2-devel@oss.oracle.com Hi, Junxiao On 2016/1/12 12:03, Junxiao Bi wrote: > Hi Jiufei, > > On 01/11/2016 10:46 AM, xuejiufei wrote: >> Hi all, >> We have found a race between refmap setting and clearing which >> will cause the lock resource on master is freed before other nodes >> purge it. >> >> Node 1 Node 2(master) >> dlm_do_master_request >> dlm_master_request_handler >> -> dlm_lockres_set_refmap_bit >> call dlm_purge_lockres after unlock >> dlm_deref_handler >> -> find lock resource is in >> DLM_LOCK_RES_SETREF_INPROG state, >> so dispatch a deref work >> dlm_purge_lockres succeed. >> >> dlm_do_master_request >> dlm_master_request_handler >> -> dlm_lockres_set_refmap_bit >> >> deref work trigger, call >> dlm_lockres_clear_refmap_bit >> to clear Node 1 from refmap >> >> Now Node 2 can purge the lock resource but the owner of lock resource >> on Node 1 is still Node 2 which may trigger BUG if the lock resource >> is $RECOVERY or other problems. >> >> We have discussed 2 solutions: >> 1)The master return error to Node 1 if the DLM_LOCK_RES_SETREF_INPROG >> is set. Node 1 will not retry and master send another message to Node 1 >> after clearing the refmap. Node 1 can purge the lock resource after the >> refmap on master is cleared. >> 2) The master return error to Node 1 if the DLM_LOCK_RES_SETREF_INPROG >> is set, and Node 1 will retry to deref the lockres. >> >> Does anybody has better ideas? >> > dlm_purge_lockres() will wait to drop ref until > DLM_LOCK_RES_SETREF_INPROG cleared. So if set this flag when find the > master during doing master request. And then this flag was cleared when > receiving assert master message, can this fix the issue? > I don't think this can fix. Before doing master request, the lock resource is already purged. The master should clear the refmap before client purge it. Thanks, Jiufei > Thanks, > Junxiao. >> Thanks, >> --Jiufei >> > > > . >