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

[Changwei Ge]

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.

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 */
>>
>