piaojun
2018-Jan-19 03:59 UTC
[Ocfs2-devel] [Ocfs2-dev] BUG: deadlock with umount and ocfs2 workqueue triggered by ocfs2rec thread
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: >>>>>>> [<ffffffff8a8c0694>] call_rwsem_down_read_failed+0x14/0x30 >>>>>>> [<ffffffffc0d5d652>] ocfs2_finish_quota_recovery+0x62/0x450 [ocfs2] >>>>>>> [<ffffffffc0d21221>] ocfs2_complete_recovery+0xc1/0x440 [ocfs2] >>>>>>> [<ffffffff8a09a1f0>] process_one_work+0x130/0x350 >>>>>>> [<ffffffff8a09a946>] worker_thread+0x46/0x3b0 >>>>>>> [<ffffffff8a0a0e51>] kthread+0x101/0x140 >>>>>>> [<ffffffff8aa002ff>] ret_from_fork+0x1f/0x30 >>>>>>> [<ffffffffffffffff>] 0xffffffffffffffff >>>>>>> >>>>>>> /bin/umount: >>>>>>> [<ffffffff8a099b24>] flush_workqueue+0x104/0x3e0 >>>>>>> [<ffffffffc0cf18db>] ocfs2_truncate_log_shutdown+0x3b/0xc0 [ocfs2] >>>>>>> [<ffffffffc0d4fd6c>] ocfs2_dismount_volume+0x8c/0x3d0 [ocfs2] >>>>>>> [<ffffffffc0d500e1>] ocfs2_put_super+0x31/0xa0 [ocfs2] >>>>>>> [<ffffffff8a2445bd>] generic_shutdown_super+0x6d/0x120 >>>>>>> [<ffffffff8a24469d>] kill_block_super+0x2d/0x60 >>>>>>> [<ffffffff8a244e71>] deactivate_locked_super+0x51/0x90 >>>>>>> [<ffffffff8a263a1b>] cleanup_mnt+0x3b/0x70 >>>>>>> [<ffffffff8a09e9c6>] task_work_run+0x86/0xa0 >>>>>>> [<ffffffff8a003d70>] exit_to_usermode_loop+0x6d/0xa9 >>>>>>> [<ffffffff8a003a2d>] do_syscall_64+0x11d/0x130 >>>>>>> [<ffffffff8aa00113>] entry_SYSCALL64_slow_path+0x25/0x25 >>>>>>> [<ffffffffffffffff>] 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 >>> >> > . >
Changwei Ge
2018-Jan-19 05:42 UTC
[Ocfs2-devel] [Ocfs2-dev] BUG: deadlock with umount and ocfs2 workqueue triggered by ocfs2rec thread
Hi Jun, On 2018/1/19 11:59, piaojun wrote:> 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'?I am not pointing to super_block. Sure. You can refer to ocfs2_finish_quota_recovery ocfs2_recover_local_quota_file -> here, operations on quota happens Thanks, Changwei> > 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: >>>>>>>> [<ffffffff8a8c0694>] call_rwsem_down_read_failed+0x14/0x30 >>>>>>>> [<ffffffffc0d5d652>] ocfs2_finish_quota_recovery+0x62/0x450 [ocfs2] >>>>>>>> [<ffffffffc0d21221>] ocfs2_complete_recovery+0xc1/0x440 [ocfs2] >>>>>>>> [<ffffffff8a09a1f0>] process_one_work+0x130/0x350 >>>>>>>> [<ffffffff8a09a946>] worker_thread+0x46/0x3b0 >>>>>>>> [<ffffffff8a0a0e51>] kthread+0x101/0x140 >>>>>>>> [<ffffffff8aa002ff>] ret_from_fork+0x1f/0x30 >>>>>>>> [<ffffffffffffffff>] 0xffffffffffffffff >>>>>>>> >>>>>>>> /bin/umount: >>>>>>>> [<ffffffff8a099b24>] flush_workqueue+0x104/0x3e0 >>>>>>>> [<ffffffffc0cf18db>] ocfs2_truncate_log_shutdown+0x3b/0xc0 [ocfs2] >>>>>>>> [<ffffffffc0d4fd6c>] ocfs2_dismount_volume+0x8c/0x3d0 [ocfs2] >>>>>>>> [<ffffffffc0d500e1>] ocfs2_put_super+0x31/0xa0 [ocfs2] >>>>>>>> [<ffffffff8a2445bd>] generic_shutdown_super+0x6d/0x120 >>>>>>>> [<ffffffff8a24469d>] kill_block_super+0x2d/0x60 >>>>>>>> [<ffffffff8a244e71>] deactivate_locked_super+0x51/0x90 >>>>>>>> [<ffffffff8a263a1b>] cleanup_mnt+0x3b/0x70 >>>>>>>> [<ffffffff8a09e9c6>] task_work_run+0x86/0xa0 >>>>>>>> [<ffffffff8a003d70>] exit_to_usermode_loop+0x6d/0xa9 >>>>>>>> [<ffffffff8a003a2d>] do_syscall_64+0x11d/0x130 >>>>>>>> [<ffffffff8aa00113>] entry_SYSCALL64_slow_path+0x25/0x25 >>>>>>>> [<ffffffffffffffff>] 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 >>>> >>> >> . >> >