[LTP] [PATCH v4, 2/2] cgroup/cgroup_regression_test: Fix umount failure

[Joerg Vehlow]

Hi,

On 7/21/2021 4:37 PM, Petr Vorel wrote:
> Hi Leo,
>
> Reviewed-by: Petr Vorel <pvorel@suse.cz>
>
>>   	rmdir cgroup/0 cgroup/1
>> -	umount cgroup/
>> +	tst_umount cgroup/	# Avoid possible EBUSY error
>>   }
>>   #---------------------------------------------------------------------------
>> @@ -193,7 +193,7 @@ test3()
>>   	wait $pid2 2>/dev/null
>>   	rmdir $cpu_subsys_path/0 2> /dev/null
>> -	umount cgroup/ 2> /dev/null
>> +	tst_umount cgroup/ 2> /dev/null		# Avoid possible EBUSY error
> I'd prefer: # keep "/" to avoid possible EBUSY error
> But that can be changed before merge.
>
> More I'm interested if other maintainers agree with me about this approach.
> (keep / here instead of in tst_umount())
I had a first look at this patches and was curious, what the reasoning 
behind the "/" is.
The comment you suggest is wrong. The / was introduced to prevent 
unmounting some other mountpoint,
where the device was cgroup.
Imho the approach of adding a / to the end was wrong and intransparent. 
I would rather use "./cgroup" or "$PWD/cgroup".
If possible, I'd actually change tst_umount, to always unmount the 
mountpoint and not the device, i.e. if the given path is not an absolute 
path, make it absolute (e.g. by prepending $PWD").
This way the check if the mountpoint exist wouldn't be the fuzzy thing 
it is right now.

As for the comment ("# Avoid possible EBUSY error"): Honestly I'd drop 
it and like in the c-api make using tst_umount instead of plain umount 
the default, for the same reasons.

>>   	if dmesg | grep -q "MAX_LOCKDEP_SUBCLASSES too low"; then
>>   		tst_res TFAIL "lockdep BUG was found"
>> @@ -254,7 +254,7 @@ test5()
>>   	mount -t cgroup none cgroup 2> /dev/null
>>   	mkdir cgroup/0
>>   	rmdir cgroup/0
>> -	umount cgroup/ 2> /dev/null
>> +	tst_umount cgroup/ 2> /dev/null		# Avoid possible EBUSY error
> I'd drop stderr redirection here. It was here originally, but I suppose it's not
> needed when using tst_umount. But that can be done during merge.
+1

Joerg