Messages in this thread | | | Subject | Re: [PATCH] ocfs2: reflink deadlock when clone file to the same directory simultaneously | From | Gang He <> | Date | Thu, 19 Aug 2021 14:31:36 +0800 |
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On 2021/8/19 10:02, Joseph Qi wrote: > > > On 8/19/21 9:51 AM, Gang He wrote: >> >> >> On 2021/8/18 19:20, Joseph Qi wrote: >>> >>> >>> On 8/18/21 5:20 PM, Gang He wrote: >>>> >>>> >>>> On 2021/8/13 17:54, Joseph Qi wrote: >>>>> >>>>> >>>>> On 8/9/21 6:08 PM, Gang He wrote: >>>>>> Hi Joseph and All, >>>>>> >>>>>> The deadlock is caused by self-locking on one node. >>>>>> There is three node cluster (mounted to /mnt/shared), the user run reflink command to clone the file to the same directory repeatedly, >>>>>> e.g. >>>>>> reflink "/mnt/shared/test" \ >>>>>> "/mnt/shared/.snapshots/test.`date +%m%d%H%M%S`.`hostname`" >>>>>> >>>>>> After a while, the reflink process on each node is hung, the file system cannot be listed. >>>>>> The problematic reflink command process is blocked by itself, e.g. the reflink process is hung at ghe-sle15sp2-nd2, >>>>>> kernel: task:reflink state:D stack: 0 pid:16992 ppid: 4530 >>>>>> kernel: Call Trace: >>>>>> kernel: __schedule+0x2fd/0x750 >>>>>> kernel: ? try_to_wake_up+0x17b/0x4e0 >>>>>> kernel: schedule+0x2f/0xa0 >>>>>> kernel: schedule_timeout+0x1cc/0x310 >>>>>> kernel: ? __wake_up_common+0x74/0x120 >>>>>> kernel: wait_for_completion+0xba/0x140 >>>>>> kernel: ? wake_up_q+0xa0/0xa0 >>>>>> kernel: __ocfs2_cluster_lock.isra.41+0x3b5/0x820 [ocfs2] >>>>>> kernel: ? ocfs2_inode_lock_full_nested+0x1fc/0x960 [ocfs2] >>>>>> kernel: ocfs2_inode_lock_full_nested+0x1fc/0x960 [ocfs2] >>>>>> kernel: ocfs2_init_security_and_acl+0xbe/0x1d0 [ocfs2] >>>>>> kernel: ocfs2_reflink+0x436/0x4c0 [ocfs2] >>>>>> kernel: ? ocfs2_reflink_ioctl+0x2ca/0x360 [ocfs2] >>>>>> kernel: ocfs2_reflink_ioctl+0x2ca/0x360 [ocfs2] >>>>>> kernel: ocfs2_ioctl+0x25e/0x670 [ocfs2] >>>>>> kernel: do_vfs_ioctl+0xa0/0x680 >>>>>> kernel: ksys_ioctl+0x70/0x80 >>>>>> >>>>>> In fact, the destination directory(.snapshots) inode dlm lock was acquired by ghe-sle15sp2-nd2, next there is bast message from other nodes to ask ghe-sle15sp2-nd2 downconvert lock, but the operation failed, the kernel message is printed like, >>>>>> kernel: (ocfs2dc-AA35DD9,2560,3):ocfs2_downconvert_lock:3660 ERROR: DLM error -16 while calling ocfs2_dlm_lock on resource M0000000000000000046e0200000000 >>>>>> kernel: (ocfs2dc-AA35DD9,2560,3):ocfs2_unblock_lock:3904 ERROR: status = -16 >>>>>> kernel: (ocfs2dc-AA35DD9,2560,3):ocfs2_process_blocked_lock:4303 ERROR: status = -16 >>>>>> >>>>>> Then, the reflink process tries to acquire this directory inode dlm lock, the process is blocked, the dlm lock resource in memory looks like >>>>>> >>>>>> l_name = "M0000000000000000046e0200000000", >>>>>> l_ro_holders = 0, >>>>>> l_ex_holders = 0, >>>>>> l_level = 5 '\005', >>>>>> l_requested = 0 '\000', >>>>>> l_blocking = 5 '\005', >>>>>> l_type = 0 '\000', >>>>>> l_action = 0 '\000', >>>>>> l_unlock_action = 0 '\000', >>>>>> l_pending_gen = 645948, >>>>>> >>>>>> >>>>>> So far, I do not know what makes dlm lock function failed, it also looks we do not handle this failure case in dlmglue layer, but I always reproduce this hang with my test script, e.g. >>>>>> >>>>>> loop=1 >>>>>> while ((loop++)) ; do >>>>>> for i in `seq 1 100`; do >>>>>> reflink "/mnt/shared/test" "/mnt/shared/.snapshots /test.${loop}.${i}.`date +%m%d%H%M%S`.`hostname`" >>>>>> done >>>>>> usleep 500000 >>>>>> rm -f /mnt/shared/.snapshots/testnode1.qcow2.*.`hostname` >>>>>> done >>>>>> >>>>>> My patch changes multiple acquiring dest directory inode dlm lock during in ocfs2_reflink function, it avoids the hang issue happen again.The code change also can improve reflink performance in this case. >>>>>> >>>>>> Thanks >>>>>> Gang >>>>> >>>>> 'status = -16' implies DLM_CANCELGRANT. >>>>> Do you use stack user instead of o2cb? If yes, can you try o2cb with >>>>> your reproducer? >>>> >>>> I setup o2cb based ocfs2 clusters with sle15sp2 and oracleLinux8u4. >>>> After two day testing with the same script, I did not encounter dlm_lock downconvert failure, the hang issue did not happen. >>>> After my patch was applied, there was not any side effect, the reflink performance was doubled in the case. >>>> >>> >>> Do you mean the hang only happens on stack user? >> Yes. >> Why? since o2cb based dlm_lock did not return error -16 when downcovert dlm lock during the whole testing. >> But pmck based dlm_lock retuned error -16 during the testing, then we did not handle this error further in dlmglue layer, next encounter the hang issue when dlm_lock acquire the lock. Maybe there is a race condition when using dlm_lock/dlm_unlock(cancel) in dlmglue layer. >> Anyway, the problem belongs to ocfs2 own parts. >> > I meant if DLM_CANCELGRANT is not the expected return code, we'd > better fix the issue in stack_user.c but not dlmglue, e.g. some specific > wrapper. We cannot wrapper(or ignore) this error in stack_user, otherwise it will lead to a hang problem when the next dlm_lock is invoked. Based on comments from fs/dlm maintainer, the error -16 is returned by dlm_lock in case ocfs2 calls dlm_unlock(CANCEL) to cancel an in-progress dlm_lock() request. In fact, if you read the code comments in dlmglue.c, it also talked about the similar situation, but I feel the current code should still has a race condition, then trigger dlm_lock return -16 error. For o2cb stack, it's dlm_lock did not expose this error, maybe it is different in dlm implementation.
Thanks Gang
> > Thanks, > Joseph >
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