[linux-lvm] issue about return value in _lvchange_activate_single

[heming.zhao at suse.com]

On 11/17/20 11:45 PM, David Teigland wrote:
> On Tue, Nov 17, 2020 at 11:52:28AM +0800, heming.zhao at suse.com wrote:
>> In lvm functions, it treats "return 0" as error case.
>>
>> if _lvchange_activate() return ECMD_FAILED, the caller _lvchange_activate_single() think as normal:
>> ```
>> if (!_lvchange_activate(cmd, lv)) <== ECMD_FAILED is 5, won't enter if case.
>>          return_ECMD_FAILED;
> 
> Thanks for finding that.  In some places 0 is the error value and in other
> places ECMD_FAILED is the error value; they frequently get mixed up.
> I believe this is the bug you are seeing:
> https://sourceware.org/git/?p=lvm2.git;a=commit;h=aba9652e584b6f6a422233dea951eb59326a3de2
> 

I recommend to use a define (e.g. E_COMM_ERR) not magic number (ZERO) to replace return value. 

>> 2. node2 change the systemid to itself
>>
>> ```
>> [tb-clustermd2 ~]# vgchange -y --config "local/extra_system_ids='tb-clustermd1'" --systemid tb-clustermd2 vg1
>>    Volume group "vg1" successfully changed
>> [tb-clustermd2 ~]# lvchange -ay vg1/lv1
>> [tb-clustermd2 ~]# dmsetup ls
>> vg1-lv1 (254:0)
> 
> This is what the LVM-activate resource agent does, except it wouldn't be
> done while the LV is active on another running host.  Just wanted to
> clarify that, I don't think it's the point of your illustration here.
> 
>> 3. this time both sides have dm device.
>> ```
>> [tb-clustermd1 ~]# dmsetup ls
>> vg1-lv1 (254:0)
>> [tb-clustermd2 ~]# dmsetup ls
>> vg1-lv1 (254:0)
>> ```
> 
> For the sake of anyone looking at this later, this shouldn't happen in a
> properly running cluster.  (If you wanted the LV active on two hosts at
> once, you'd use lvmlockd and no system ID on the VG.)
> 
>> 4. node1 executes lvchange cmds. please note the return value is 0
>> ```
>> [tb-clustermd1 ~]# lvchange -ay vg1/lv1 ; echo $?
>>    WARNING: Found LVs active in VG vg1 with foreign system ID tb-clustermd2.  Possible data corruption.
>>    Cannot activate LVs in a foreign VG.
>> 0
> 
> That's the one fixed by the commit above.
> 
> Dave
>