[Ocfs2-devel] [patch 04/15] ocfs2: avoid access invalid address when read o2dlm debug messages

[jiangyiwen <jiangyiwen@huawei.com>]

? 2014/12/23 14:06, Xue jiufei ??:
> Hi jiangyiwen,
> On 2014/12/20 17:39, jiangyiwen wrote:
>> ? 2014/12/20 4:25, Mark Fasheh ??:
>>> On Fri, Dec 19, 2014 at 04:34:39PM +0800, jiangyiwen wrote:
>>>> ? 2014/12/17 6:26, Mark Fasheh ??:
>>>>> On Mon, Dec 15, 2014 at 02:51:00PM -0800, Andrew Morton wrote:
>>>>>> In such a race case, invalid address access may occurs.  So we should
>>>>>> delete list res->tracking before resA->refs decrease to 0.
>>>>>>
>>>>>
>>>>>
>>>>>> diff -puN fs/ocfs2/dlm/dlmmaster.c~ocfs2-avoid-access-invalid-address-when-read-o2dlm-debug-messages fs/ocfs2/dlm/dlmmaster.c
>>>>>> --- a/fs/ocfs2/dlm/dlmmaster.c~ocfs2-avoid-access-invalid-address-when-read-o2dlm-debug-messages
>>>>>> +++ a/fs/ocfs2/dlm/dlmmaster.c
>>>>>> @@ -498,16 +498,6 @@ static void dlm_lockres_release(struct k
>>>>>>  	mlog(0, "destroying lockres %.*s\n", res->lockname.len,
>>>>>>  	     res->lockname.name);
>>>>>>  
>>>>>> -	spin_lock(&dlm->track_lock);
>>>>>> -	if (!list_empty(&res->tracking))
>>>>>> -		list_del_init(&res->tracking);
>>>>>> -	else {
>>>>>> -		mlog(ML_ERROR, "Resource %.*s not on the Tracking list\n",
>>>>>> -		     res->lockname.len, res->lockname.name);
>>>>>> -		dlm_print_one_lock_resource(res);
>>>>>> -	}
>>>>>> -	spin_unlock(&dlm->track_lock);
>>>>>> -
>>>>>>  	atomic_dec(&dlm->res_cur_count);
>>>>>>  
>>>>>>  	if (!hlist_unhashed(&res->hash_node) ||
>>>>>> diff -puN fs/ocfs2/dlm/dlmthread.c~ocfs2-avoid-access-invalid-address-when-read-o2dlm-debug-messages fs/ocfs2/dlm/dlmthread.c
>>>>>> --- a/fs/ocfs2/dlm/dlmthread.c~ocfs2-avoid-access-invalid-address-when-read-o2dlm-debug-messages
>>>>>> +++ a/fs/ocfs2/dlm/dlmthread.c
>>>>>> @@ -211,6 +211,16 @@ static void dlm_purge_lockres(struct dlm
>>>>>>  
>>>>>>  	__dlm_unhash_lockres(dlm, res);
>>>>>>  
>>>>>> +	spin_lock(&dlm->track_lock);
>>>>>> +	if (!list_empty(&res->tracking))
>>>>>> +		list_del_init(&res->tracking);
>>>>>> +	else {
>>>>>> +		mlog(ML_ERROR, "Resource %.*s not on the Tracking list\n",
>>>>>> +				res->lockname.len, res->lockname.name);
>>>>>> +		__dlm_print_one_lock_resource(res);
>>>>>> +	}
>>>>>> +	spin_unlock(&dlm->track_lock);
>>>>>> +
>>>>>>  	/* lockres is not in the hash now.  drop the flag and wake up
>>>>>>  	 * any processes waiting in dlm_get_lock_resource. */
>>>>>>  	if (!master) {
>>>>>> _
>>>>>
>>>>> How do we know that dlm_purge_lockres() is the last caller of
>>>>> dlm_lockres_put()? Don't we now have a problem where if the last ref is
>>>>> dropped by any other function than dlm_purge_lockres() the lockres is freed
>>>>> while on the tracking list?
>>>>> 	--Mark
>>>>>
>>>>> --
>>>>> Mark Fasheh
>>>>>
>>>>> .
>>>>>
>>>> dlm_purge_lockres is not necessarily the last caller of
>>>> dlm_lockres_put(), but it means lockres will be purged if
>>>> dlm_purge_lockres is called. Besides, lockres is also unhashed in
>>>> dlm_purge_lockres, so lockres can be removed from tracking list.
>>>> contents of dlm->tracking_list will be consistent with
>>>> dlm->lockres_hash.
>>>
>>> I'm still confused. This is what I'm worried about:
>>>
>>> 1) a procss calls dlm_lockres_put(), NOT from dlm_purge_lockres().
>>>
>>> 2) if the count goes to zero, then that process will call dlm_lockres_release()
>>>
>> But at this time, it has already called dlm_purge_lockres(). The reasons are as follows:
>> 1) lockres is created in dlm_init_lockres(), it call kref_init(), count is 1;
>> 2) Only when lockres is unused, it will call dlm_lockres_put() twice by dlm_run_purge_list().
>> So dlm_purge_lockres() has been called if the count goes to zero.
>>
>>> 3) dlm_lockres_release() will free the lockres without removing it from the
>>> tracking list. Thus we will have a corrupted list.
>>>
>> Without this scene. dlm_purge_lockres() is called before dlm_lockres_release().
> Once lock resource is inserted into hash list, it should call
> dlm_purge_lockres()->__dlm_unhash_lockres() to put the last ref.
> However, if lock resource is initialized and inserted into tracking
> list but not inserted into hash list, it can happen that
> dlm_lockres_release() will free the lockres without removing it from
> the tracking list.
> So we should remove lockres from tracking list if we call
> dlm_lockres_put() after lockres is created but not inserted into hash
> list yet.
> 
> Thanks,
> Xuejiufei
Thanks, you are right! I will send new version later.
	--Yiwen Jiang

>>> Does that make sense? Am I wrong here?
>>> 	--Mark
>>>
>>> --
>>> Mark Fasheh
>>>
>>> .
>>>
>>
>>
>>
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> 
> 
> 
> .
>