[Ocfs2-devel] ocfs2: A race between refmap setting and clearing

[Junxiao Bi <junxiao.bi@oracle.com>]

Hi Jiufei,

I didn't find other solution for this issue. You can go with yours.
Looks like your second one is more straightforward, there deref work can
be removed.

Thanks,
Junxiao.
On 01/11/2016 10:46 AM, xuejiufei wrote:
> Hi all,
> We have found a race between refmap setting and clearing which
> will cause the lock resource on master is freed before other nodes
> purge it.
> 
> Node 1                               Node 2(master)
> dlm_do_master_request
>                                 dlm_master_request_handler
>                                 -> dlm_lockres_set_refmap_bit
> call dlm_purge_lockres after unlock
>                                 dlm_deref_handler
>                                 -> find lock resource is in
>                                    DLM_LOCK_RES_SETREF_INPROG state,
>                                    so dispatch a deref work
> dlm_purge_lockres succeed.
> 
> dlm_do_master_request
>                                 dlm_master_request_handler
>                                 -> dlm_lockres_set_refmap_bit
> 
>                                 deref work trigger, call
>                                 dlm_lockres_clear_refmap_bit
>                                 to clear Node 1 from refmap
> 
> Now Node 2 can purge the lock resource but the owner of lock resource
> on Node 1 is still Node 2 which may trigger BUG if the lock resource
> is $RECOVERY or other problems.
> 
> We have discussed 2 solutions:
> 1)The master return error to Node 1 if the DLM_LOCK_RES_SETREF_INPROG
> is set. Node 1 will not retry and master send another message to Node 1
> after clearing the refmap. Node 1 can purge the lock resource after the
> refmap on master is cleared.
> 2) The master return error to Node 1 if the DLM_LOCK_RES_SETREF_INPROG
> is set, and Node 1 will retry to deref the lockres.
> 
> Does anybody has better ideas?
> 
> Thanks,
> --Jiufei
>