[Ocfs2-devel] [PATCH] ocfs2: wait for recovering done after direct unlock request

[piaojun]

Hi Changwei,

Thanks for your explaination, and I still have a question below.

On 2019/2/15 14:29, Changwei Ge wrote:
> Hi Jun,
> 
> On 2019/2/15 14:20, piaojun wrote:
>> Hi Changwei,
>>
>> The DLM process is a little bit complex, so I suggest pasting the code
>> path. And I wonder if my code is right?
>>
>> Thanks,
>> Jun
>>
>> On 2019/2/14 14:14, Changwei Ge wrote:
>>> There is scenario causing ocfs2 umount hang when multiple hosts are
>>> rebooting at the same time.
>>>
>>> NODE1                           NODE2               NODE3
>>> send unlock requset to NODE2
>>>                                  dies
>>>                                                      become recovery master
>>>                                                      recover NODE2
>>> find NODE2 dead
>>> mark resource RECOVERING
>>> directly remove lock from grant list
>> dlm_do_local_recovery_cleanup
>>    dlm_move_lockres_to_recovery_list
>>      res->state |= DLM_LOCK_RES_RECOVERING;
>>      list_add_tail(&res->recovering, &dlm->reco.resources);
>>
>>> calculate usage but RECOVERING marked
>>> **miss the window of purging
>> dlmunlock
>>    dlmunlock_remote
>>      dlmunlock_common // unlock successfully directly
>>
>>    dlm_lockres_calc_usage
>>      __dlm_lockres_calc_usage
>>        __dlm_lockres_unused
>>          if (res->state & (DLM_LOCK_RES_RECOVERING| // won't purge lock as DLM_LOCK_RES_RECOVERING is set
> 
> True.
> 
>>
>>> clear RECOVERING
>> dlm_finish_local_lockres_recovery
>>    res->state &= ~DLM_LOCK_RES_RECOVERING;
>>
>> Could you help explaining where getting stuck?
> 
> Sure,
> As dlm missed the window to purge lock resource, it can't be unhashed.
> 
> During umount:
> dlm_unregister_domain
>    dlm_migrate_all_locks -> there is always a lock resource hashed, so can't return from dlm_migrate_all_locks() thus hang during umount.

In dlm_migrate_all_locks, lockres will be move to purge_list and purged again:
dlm_migrate_all_locks
  __dlm_lockres_calc_usage
    list_add_tail(&res->purge, &dlm->purge_list);

Do you mean this process does not work?

> 
> Thanks,
> Changwei
> 	
> 
>>
>>>
>>> To reproduce this iusse, crash a host and then umount ocfs2
>>> from another node.
>>>
>>> To sovle this, just let unlock progress wait for recovery done.
>>>
>>> Signed-off-by: Changwei Ge <ge.changwei at h3c.com>
>>> ---
>>>   fs/ocfs2/dlm/dlmunlock.c | 23 +++++++++++++++++++----
>>>   1 file changed, 19 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/fs/ocfs2/dlm/dlmunlock.c b/fs/ocfs2/dlm/dlmunlock.c
>>> index 63d701c..c8e9b70 100644
>>> --- a/fs/ocfs2/dlm/dlmunlock.c
>>> +++ b/fs/ocfs2/dlm/dlmunlock.c
>>> @@ -105,7 +105,8 @@ static enum dlm_status dlmunlock_common(struct dlm_ctxt *dlm,
>>>   	enum dlm_status status;
>>>   	int actions = 0;
>>>   	int in_use;
>>> -        u8 owner;
>>> +	u8 owner;
>>> +	int recovery_wait = 0;
>>>   
>>>   	mlog(0, "master_node = %d, valblk = %d\n", master_node,
>>>   	     flags & LKM_VALBLK);
>>> @@ -208,9 +209,12 @@ static enum dlm_status dlmunlock_common(struct dlm_ctxt *dlm,
>>>   		}
>>>   		if (flags & LKM_CANCEL)
>>>   			lock->cancel_pending = 0;
>>> -		else
>>> -			lock->unlock_pending = 0;
>>> -
>>> +		else {
>>> +			if (!lock->unlock_pending)
>>> +				recovery_wait = 1;
>>> +			else
>>> +				lock->unlock_pending = 0;
>>> +		}
>>>   	}
>>>   
>>>   	/* get an extra ref on lock.  if we are just switching
>>> @@ -244,6 +248,17 @@ static enum dlm_status dlmunlock_common(struct dlm_ctxt *dlm,
>>>   	spin_unlock(&res->spinlock);
>>>   	wake_up(&res->wq);
>>>   
>>> +	if (recovery_wait) {
>>> +		spin_lock(&res->spinlock);
>>> +		/* Unlock request will directly succeed after owner dies,
>>> +		 * and the lock is already removed from grant list. We have to
>>> +		 * wait for RECOVERING done or we miss the chance to purge it
>>> +		 * since the removement is much faster than RECOVERING proc.
>>> +		 */
>>> +		__dlm_wait_on_lockres_flags(res, DLM_LOCK_RES_RECOVERING);
>>> +		spin_unlock(&res->spinlock);
>>> +	}
>>> +
>>>   	/* let the caller's final dlm_lock_put handle the actual kfree */
>>>   	if (actions & DLM_UNLOCK_FREE_LOCK) {
>>>   		/* this should always be coupled with list removal */
>>>
>>
> .
>