From mboxrd@z Thu Jan 1 00:00:00 1970 From: piaojun Date: Fri, 19 Jan 2018 11:59:17 +0800 Subject: [Ocfs2-devel] [Ocfs2-dev] BUG: deadlock with umount and ocfs2 workqueue triggered by ocfs2rec thread In-Reply-To: <63ADC13FD55D6546B7DECE290D39E373F2912961@H3CMLB12-EX.srv.huawei-3com.com> References: <0044cc89-5cda-c4a9-5eb0-1e5d85416805@suse.com> <20180117152135.nhiho7agzxige6xl@quack2.suse.cz> <20180117155734.ntkwdbvbkikh6dcl@quack2.suse.cz> <63ADC13FD55D6546B7DECE290D39E373F2912842@H3CMLB12-EX.srv.huawei-3com.com> <5A616313.4070403@huawei.com> <63ADC13FD55D6546B7DECE290D39E373F2912961@H3CMLB12-EX.srv.huawei-3com.com> Message-ID: <5A616D15.3060101@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 Changwei, On 2018/1/19 11:38, Changwei Ge wrote: > Hi Jun, > > On 2018/1/19 11:17, piaojun wrote: >> Hi Jan, Eric and Changwei, >> >> Could we use another mutex lock to protect quota recovery? Sharing the >> lock with VFS-layer probably seems a little weird. > > I am afraid that we can't since quota need ::s_umount and we indeed need > ::s_umount to get rid of race that quota has freed structs that will be > used by quota recovery in ocfs2. > Could you explain which 'structs' used by quota recovery? Do you mean 'struct super_block'? thanks, Jun >> >> On 2018/1/19 9:48, Changwei Ge wrote: >>> Hi Jan, >>> >>> On 2018/1/18 0:03, Jan Kara wrote: >>>> On Wed 17-01-18 16:21:35, Jan Kara wrote: >>>>> Hello, >>>>> >>>>> On Fri 12-01-18 16:25:56, Eric Ren wrote: >>>>>> On 01/12/2018 11:43 AM, Shichangkuo wrote: >>>>>>> Hi all, >>>>>>> ??Now we are testing ocfs2 with 4.14 kernel, and we finding a deadlock with umount and ocfs2 workqueue triggered by ocfs2rec thread. The stack as follows: >>>>>>> journal recovery work: >>>>>>> [] call_rwsem_down_read_failed+0x14/0x30 >>>>>>> [] ocfs2_finish_quota_recovery+0x62/0x450 [ocfs2] >>>>>>> [] ocfs2_complete_recovery+0xc1/0x440 [ocfs2] >>>>>>> [] process_one_work+0x130/0x350 >>>>>>> [] worker_thread+0x46/0x3b0 >>>>>>> [] kthread+0x101/0x140 >>>>>>> [] ret_from_fork+0x1f/0x30 >>>>>>> [] 0xffffffffffffffff >>>>>>> >>>>>>> /bin/umount: >>>>>>> [] flush_workqueue+0x104/0x3e0 >>>>>>> [] ocfs2_truncate_log_shutdown+0x3b/0xc0 [ocfs2] >>>>>>> [] ocfs2_dismount_volume+0x8c/0x3d0 [ocfs2] >>>>>>> [] ocfs2_put_super+0x31/0xa0 [ocfs2] >>>>>>> [] generic_shutdown_super+0x6d/0x120 >>>>>>> [] kill_block_super+0x2d/0x60 >>>>>>> [] deactivate_locked_super+0x51/0x90 >>>>>>> [] cleanup_mnt+0x3b/0x70 >>>>>>> [] task_work_run+0x86/0xa0 >>>>>>> [] exit_to_usermode_loop+0x6d/0xa9 >>>>>>> [] do_syscall_64+0x11d/0x130 >>>>>>> [] entry_SYSCALL64_slow_path+0x25/0x25 >>>>>>> [] 0xffffffffffffffff >>>>>>> ?? >>>>>>> Function ocfs2_finish_quota_recovery try to get sb->s_umount, which was already locked by umount thread, then get a deadlock. >>>>>> >>>>>> Good catch, thanks for reporting. Is it reproducible? Can you please share >>>>>> the steps for reproducing this issue? >>>>>>> This issue was introduced by c3b004460d77bf3f980d877be539016f2df4df12 and 5f530de63cfc6ca8571cbdf58af63fb166cc6517. >>>>>>> I think we cannot use :: s_umount, but the mutex ::dqonoff_mutex was already removed. >>>>>>> Shall we add a new mutex? >>>>>> >>>>>> @Jan, I don't look into the code yet, could you help me understand why we >>>>>> need to get sb->s_umount in ocfs2_finish_quota_recovery? >>>>>> Is it because that the quota recovery process will start at umounting? or >>>>>> some where else? >>>>> >>>>> I was refreshing my memory wrt how ocfs2 quota recovery works. The problem >>>>> is the following: We load information about all quota information that >>>>> needs recovering (this is possibly for other nodes) in >>>>> ocfs2_begin_quota_recovery() that gets called during mount. Real quota >>>>> recovery happens from the recovery thread in ocfs2_finish_quota_recovery(). >>>>> We need to protect code running there from dquot_disable() calls as that >>>>> will free structures we use for updating quota information etc. Currently >>>>> we use sb->s_umount for that protection. >>>>> >>>>> The problem above apparently happens when someone calls umount before the >>>>> recovery thread can finish quota recovery. I will think more about how to >>>>> fix the locking so that this lock inversion does not happen... >>>> >>>> So could we move ocfs2_recovery_exit() call in ocfs2_dismount_volume() up >>>> before ocfs2_disable_quotas()? It seems possible to me, I'm just not sure >>>> if there are not some hidden dependencies on recovery being shut down only >>>> after truncate log / local alloc. If we can do that, we could remove >>>> s_umount protection from ocfs2_finish_quota_recovery() and thus resolve the >>>> race. >>>> >>>> Honza >>> >>> Thanks for looking into this. >>> I am not quite familiar with quota part.:) >>> >>> Or can we move ocfs2_disable_quotas() in ocfs2_dismount_volume down >>> after ocfs2_recovery_exit() with ::invoking down_read(&sb->s_umount) >>> eliminated? >>> >>> Another way I can figure out is: >>> I think we might get inspired from qsync_work_fn(). >>> In that function if current work is under running context of umount with >>> ::s_umount held, it just delays current work to next time. >>> >>> So can we also _try lock_ in ocfs2_finish_quota_recovery() and recover >>> quota by other ocfs2 cluster member nodes or local node's next time of >>> mount? >>> >> I guess we need analyse the impact of _try lock_. Such as no other node >> will help recovering quota when I'm the only node in cluster. > > I don't see any risk for now. I will think about it more, later. > > Thanks, > Changwei >> >> thanks, >> Jun >> >>> Thanks, >>> Changwei >>> >>> >>>> >>> _______________________________________________ >>> Ocfs2-devel mailing list >>> Ocfs2-devel at oss.oracle.com >>> https://oss.oracle.com/mailman/listinfo/ocfs2-devel >>> >> > . >