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

[Xue jiufei <xuejiufei@huawei.com>]

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