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

[jiangyiwen <jiangyiwen@huawei.com>]

? 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.
	--YiWen Jiang