From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joseph Qi Date: Tue, 22 Sep 2015 20:23:59 +0800 Subject: [Ocfs2-devel] [PATCH v2] ocfs2/dlm: fix race between convert and recovery In-Reply-To: <5600A6FD.90901@oracle.com> References: <55FBF4BA.30000@huawei.com> <55FFCC9F.90201@huawei.com> <5600A6FD.90901@oracle.com> Message-ID: <5601485F.4030506@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 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. > > 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. >> >> > > > . >