Ocfs2 devel - Sep 2017 - [patch 1/2] ocfs2/dlm: protect 'tracking_list' by 'track_lock'

On 2017/9/25 18:35, Joseph Qi wrote:
> 
> 
> On 17/9/23 11:39, piaojun wrote:
>> 'dlm->tracking_list' need to be protected by
'dlm->track_lock'.
>>
>> Signed-off-by: Jun Piao <piaojun at huawei.com>
>> Reviewed-by: Alex Chen <alex.chen at huawei.com>
>> ---
>>  fs/ocfs2/dlm/dlmdomain.c | 7 ++++++-
>>  fs/ocfs2/dlm/dlmmaster.c | 4 ++--
>>  2 files changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/ocfs2/dlm/dlmdomain.c b/fs/ocfs2/dlm/dlmdomain.c
>> index a2b19fb..b118525 100644
>> --- a/fs/ocfs2/dlm/dlmdomain.c
>> +++ b/fs/ocfs2/dlm/dlmdomain.c
>> @@ -726,12 +726,17 @@ void dlm_unregister_domain(struct dlm_ctxt *dlm)
>>  		}
>>
>>  		/* This list should be empty. If not, print remaining lockres */
>> +		spin_lock(&dlm->track_lock);
>>  		if (!list_empty(&dlm->tracking_list)) {
>>  			mlog(ML_ERROR, "Following lockres' are still on the "
>>  			     "tracking list:\n");
>> -			list_for_each_entry(res, &dlm->tracking_list, tracking)
>> +			list_for_each_entry(res, &dlm->tracking_list, tracking) {
>> +				spin_unlock(&dlm->track_lock);
> 
> Um... If we unlock here, the iterator still has chance to be corrupted.
> 
> Thanks,
> Joseph
> 
we don't need care much about the corrupted 'tracking_list' because
we
have already picked up 'res' from 'tracking_list'. then we will
get
'track_lock' again to prevent 'tracking_list' from being
corrupted. but
I'd better make sure that 'res' is not NULL before printing, just
like:

list_for_each_entry(res, &dlm->tracking_list, tracking) {
		spin_unlock(&dlm->track_lock);
		if (res)
			dlm_print_one_lock_resource(res);
		spin_lock(&dlm->track_lock);
}

Thanks
Jun
>>  				dlm_print_one_lock_resource(res);
>> +				spin_lock(&dlm->track_lock);
>> +			}
>>  		}
>> +		spin_unlock(&dlm->track_lock);
>>
>>  		dlm_mark_domain_leaving(dlm);
>>  		dlm_leave_domain(dlm);
>> diff --git a/fs/ocfs2/dlm/dlmmaster.c b/fs/ocfs2/dlm/dlmmaster.c
>> index 3e04279..44e7d18 100644
>> --- a/fs/ocfs2/dlm/dlmmaster.c
>> +++ b/fs/ocfs2/dlm/dlmmaster.c
>> @@ -589,9 +589,9 @@ static void dlm_init_lockres(struct dlm_ctxt *dlm,
>>
>>  	res->last_used = 0;
>>
>> -	spin_lock(&dlm->spinlock);
>> +	spin_lock(&dlm->track_lock);
>>  	list_add_tail(&res->tracking, &dlm->tracking_list);
>> -	spin_unlock(&dlm->spinlock);
>> +	spin_unlock(&dlm->track_lock);
>>
>>  	memset(res->lvb, 0, DLM_LVB_LEN);
>>  	memset(res->refmap, 0, sizeof(res->refmap));
>>
> .
>

On 17/9/26 08:39, piaojun wrote:
> 
> 
> On 2017/9/25 18:35, Joseph Qi wrote:
>>
>>
>> On 17/9/23 11:39, piaojun wrote:
>>> 'dlm->tracking_list' need to be protected by
'dlm->track_lock'.
>>>
>>> Signed-off-by: Jun Piao <piaojun at huawei.com>
>>> Reviewed-by: Alex Chen <alex.chen at huawei.com>
>>> ---
>>>  fs/ocfs2/dlm/dlmdomain.c | 7 ++++++-
>>>  fs/ocfs2/dlm/dlmmaster.c | 4 ++--
>>>  2 files changed, 8 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/fs/ocfs2/dlm/dlmdomain.c b/fs/ocfs2/dlm/dlmdomain.c
>>> index a2b19fb..b118525 100644
>>> --- a/fs/ocfs2/dlm/dlmdomain.c
>>> +++ b/fs/ocfs2/dlm/dlmdomain.c
>>> @@ -726,12 +726,17 @@ void dlm_unregister_domain(struct dlm_ctxt
*dlm)
>>>  		}
>>>
>>>  		/* This list should be empty. If not, print remaining lockres */
>>> +		spin_lock(&dlm->track_lock);
>>>  		if (!list_empty(&dlm->tracking_list)) {
>>>  			mlog(ML_ERROR, "Following lockres' are still on the
"
>>>  			     "tracking list:\n");
>>> -			list_for_each_entry(res, &dlm->tracking_list, tracking)
>>> +			list_for_each_entry(res, &dlm->tracking_list, tracking)
{
>>> +				spin_unlock(&dlm->track_lock);
>>
>> Um... If we unlock here, the iterator still has chance to be corrupted.
>>
>> Thanks,
>> Joseph
>>
> 
> we don't need care much about the corrupted 'tracking_list'
because we
> have already picked up 'res' from 'tracking_list'. then we
will get
> 'track_lock' again to prevent 'tracking_list' from being
corrupted. but
> I'd better make sure that 'res' is not NULL before printing,
just like:
> 
> list_for_each_entry(res, &dlm->tracking_list, tracking) {
> 		spin_unlock(&dlm->track_lock);
> 		if (res)
> 			dlm_print_one_lock_resource(res);
> 		spin_lock(&dlm->track_lock);
> }
> 
> Thanks
> Jun
IIUC, your intent to add track lock here is to protect tracking list
when iterate the loop, right? I am saying that if unlock track lock
here, the loop is still unsafe.
Checking res here is meaningless. Maybe list_for_each_entry_safe
could work here.
BTW, how this race case happens? The above code is during umount,
what is the other flow?

Thanks,
Joseph