From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joseph Qi Date: Wed, 23 Sep 2015 15:48:44 +0800 Subject: [Ocfs2-devel] [PATCH v2] ocfs2/dlm: fix race between convert and recovery In-Reply-To: <56020774.1020102@oracle.com> References: <55FBF4BA.30000@huawei.com> <55FFCC9F.90201@huawei.com> <5600A6FD.90901@oracle.com> <5601485F.4030506@huawei.com> <5601FFA6.4020407@oracle.com> <56020495.7070306@huawei.com> <56020774.1020102@oracle.com> Message-ID: <5602595C.6000701@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 On 2015/9/23 9:59, Junxiao Bi wrote: > On 09/23/2015 09:47 AM, Joseph Qi wrote: >> On 2015/9/23 9:25, Junxiao Bi wrote: >>> On 09/22/2015 08:23 PM, Joseph Qi wrote: >>>> Hi Junxiao, >>>> >>>> On 2015/9/22 8:55, Junxiao Bi wrote: >>>>> On 09/21/2015 05:23 PM, Joseph Qi wrote: >>>>>> Hi Junxiao, >>>>>> This solution may have problem in the following scenario: >>>>>> Consider dlm_send_remote_convert_request has taken too much time, and >>>>>> dlm_move_lockres_to_recovery_list runs first and new master will see >>>>>> this node is currently in convert list after recovery. >>>>>> Then dlm_send_remote_convert_request returns other than DLM_NORMAL and >>>>>> it will revert it to grant list, then retry convert. This will makes >>>>>> this node and master inconsistent. >>>>>> I will try to find another solution to resolve the race issue. >>>>> >>>>> If master is down, no need retry convert. May check the return value of >>>>> dlm_send_remote_convert_request(), if DLM_RECOVERING, don't retry, >>>>> otherwise retry? >>>> >>>> I want to keep the original logic. And for fixing the race case I >>>> described, how about the following idea? >>>> >>>> Check the status DLM_NORMAL. If res->state is currently >>>> DLM_LOCK_RES_RECOVERING (set in dlm_move_lockres_to_recovery_list, means >>>> still in recovery) or res master changed (means new master has finished >>>> the recovery), reset the status to DLM_RECOVERING, just like the check >>>> at the beginning of dlmconvert_remote. Then it is now in grant list and >>>> outer will retry. >>> How this idea fix the race windows you described in patch log? Lock is >>> reverted to granted list but dlm_send_remote_convert_request() return >>> DLM_NORMAL. >>> >> As I described in the former mail, status is now reset to DLM_RECOVERING, >> caller will retry. And the original way will just wait forever. > I mean convert request was sent to res master successfully, > dlm_send_remote_convert_request() have return DLM_NORMAL, but before res > master send ast it panic. Looks convert will not retry in this case. > The original way is just what you said. And my idea is letting dlmlock retry by resetting status to DLM_RECOVERING in such a case. > Thanks, > Junxiao. >> >> Thanks >> Joseph >> >>> Thanks, >>> Junxiao. >>>> >>>>> >>>>> Thanks, >>>>> Junxiao. >>>>> >>>>>> >>>>>> On 2015/9/20 15:20, Junxiao Bi wrote: >>>>>>> Reviewed-by: Junxiao Bi >>>>>>> >>>>>>>>> ? 2015?9?18????7:25?Joseph Qi ??? >>>>>>>>> >>>>>>>>> There is a race window between dlmconvert_remote and >>>>>>>>> dlm_move_lockres_to_recovery_list, which will cause a lock with >>>>>>>>> OCFS2_LOCK_BUSY in grant list, thus system hangs. >>>>>>>>> >>>>>>>>> dlmconvert_remote >>>>>>>>> { >>>>>>>>> spin_lock(&res->spinlock); >>>>>>>>> list_move_tail(&lock->list, &res->converting); >>>>>>>>> lock->convert_pending = 1; >>>>>>>>> spin_unlock(&res->spinlock); >>>>>>>>> >>>>>>>>> status = dlm_send_remote_convert_request(); >>>>>>>>>>>>>>>>>>>>> race window, master has queued ast and return DLM_NORMAL, >>>>>>>>> and then down before sending ast. >>>>>>>>> this node detects master down and calls >>>>>>>>> dlm_move_lockres_to_recovery_list, which will revert the >>>>>>>>> lock to grant list. >>>>>>>>> Then OCFS2_LOCK_BUSY won't be cleared as new master won't >>>>>>>>> send ast any more because it thinks already be authorized. >>>>>>>>> >>>>>>>>> spin_lock(&res->spinlock); >>>>>>>>> lock->convert_pending = 0; >>>>>>>>> if (status != DLM_NORMAL) >>>>>>>>> dlm_revert_pending_convert(res, lock); >>>>>>>>> spin_unlock(&res->spinlock); >>>>>>>>> } >>>>>>>>> >>>>>>>>> In this case, just leave it in convert list and new master will take care >>>>>>>>> of it after recovery. And if convert request returns other than >>>>>>>>> DLM_NORMAL, convert thread will do the revert itself. So remove the >>>>>>>>> revert logic in dlm_move_lockres_to_recovery_list. >>>>>>>>> >>>>>>>>> changelog since v1: >>>>>>>>> Clean up convert_pending since it is now useless. >>>>>> >>>>>> >>>>> >>>>> >>>>> . >>>>> >>>> >>>> >>> >>> >>> . >>> >> >> > > > . >