Messages in this thread | | | Subject | Re: [PATCH] ocfs2: reflink deadlock when clone file to the same directory simultaneously | From | Gang He <> | Date | Wed, 18 Aug 2021 17:20:53 +0800 |
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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.
Thanks Gang
> > Thanks, > Joseph >
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