From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wengang Wang Date: Fri, 18 Jun 2010 10:37:38 +0800 Subject: [Ocfs2-devel] [PATCH 1/2] ocfs2 fix o2dlm dlm run purgelist In-Reply-To: <4C1A3A05.10704@oracle.com> References: <1276663383-8238-1-git-send-email-srinivas.eeda@oracle.com> <20100616060615.GB2895@laptop.us.oracle.com> <4C1A3A05.10704@oracle.com> Message-ID: <20100618023738.GA2483@laptop.us.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 10-06-17 08:06, Sunil Mushran wrote: > On 06/15/2010 11:06 PM, Wengang Wang wrote: > >still the question. > >If you have sent DEREF request to the master, and the lockres became in-use > >again, then the lockres remains in the hash table and also in the purge list. > >So > >1) If this node is the last ref, there is a possibility that the master > >purged the lockres after receiving DEREF request from this node. In this > >case, when this node does dlmlock_remote(), the lockres won't be found on the > >master. How to deal with it? > > > >2) The lockres on this node is going to be purged again, it means it will send > >secondary DEREFs to the master. This is not good I think. > > > >A thought is setting lockres->owner to DLM_LOCK_RES_OWNER_UNKNOWN after > >sending a DEREF request againt this lockres. Also redo master reqeust > >before locking on it. > > The fix we are working towards is to ensure that we set > DLM_LOCK_RES_DROPPING_REF once we are determined > to purge the lockres. As in, we should not let go of the spinlock > before we have either set the flag or decided against purging > that resource. > > Once the flag is set, new users looking up the resource via > dlm_get_lock_resource() will notice the flag and will then wait > for that flag to be cleared before looking up the lockres hash > again. If all goes well, the lockres will not be found (because it > has since been unhashed) and it will be forced to go thru the > full mastery process. That is ideal. In many cases the lockres is not got via dlm_get_lock_resource(), but via dlm_lookup_lockres()/__dlm_lookup_lockres, which doesn't set the new IN-USE state, directly. dlm_lookup_lockres() takes and drops dlm->spinlock. And some of caller of __dlm_lookup_lockres() drops the spinlock as soon as it got the lockres. Such paths access the lockres later after dropping dlm->spinlock and res->spinlock. So there is a window that dlm_thread() get a chance to take the dlm->spinlock and res->spinlock and set the DROPPING_REF state. So whether new users can get the lockres depends on how "new" it is. If finds the lockres after DROPPING_REF state is set, sure it works well. But if it find it before DROPPING_REF is set, it won't protect the lockres from purging since even it "gets" the lockres, the lockres can still in unused state. regards, wengang.