[LTP] [PATCH] cgroup_regression_test.sh: fix test_5 possible mount failure because of cgroup hierarchy

[Yang Xu <xuyang2018.jy@cn.fujitsu.com>]

Hi 

Ping.  :-) 

> Currently, if systems doesn't mount subsys1,subsys2 and the hierarchy is not equal to 0, running it
> reports the following error:
>
> mount: xxx is already mounted or /tmp/ltp-wPw08anmTI/LTP_cgroup_regression_test.V4jf0qrS7z/cgroup busy
> cgroup_regression_test 5 TFAIL: mount net_prio and pids failed
>
> It fails because libcgroup doesn't permmit destroy cgroup subsystem hierarchies.
> Simple umnout does not destroy the hierarchies. They still live inside kernel!
>
> When  hierarchy is equal to 0 in /proc/cgroups, we can mount them together on
> a new mountpoint.
>
> I add a check for subsystem hierarchy and get subsystem from head.
>
> Notice:
> more information about"Bug 612805 - cgroup: mount: none already mounted or /cgroups busy"
>
> Signed-off-by: Yang Xu <xuyang2018.jy@cn.fujitsu.com>
> ---
>  .../cgroup/cgroup_regression_test.sh           | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/testcases/kernel/controllers/cgroup/cgroup_regression_test.sh b/testcases/kernel/controllers/cgroup/cgroup_regression_test.sh
> index e197f5d3f..38cb760c2 100755
> --- a/testcases/kernel/controllers/cgroup/cgroup_regression_test.sh
> +++ b/testcases/kernel/controllers/cgroup/cgroup_regression_test.sh
> @@ -252,8 +252,10 @@ test5()
>  		return
>  	fi
>  
> -	local subsys1=`tail -n 1 /proc/cgroups | awk '{ print $1 }'`
> -	local subsys2=`tail -n 2 /proc/cgroups | head -1 | awk '{ print $1 }'`
> +	local subsys1=`head -2 /proc/cgroups | tail -n 1 | awk '{ print $1 }'`
> +	local subsys1_hierarchy=`head -2 /proc/cgroups | tail -n 1 | awk '{ print $2 }'`
> +	local subsys2=`head -3 /proc/cgroups | tail -n 1 | awk '{ print $1 }'`
> +	local subsys2_hierarchy=`head -3 /proc/cgroups | tail -n 1 | awk '{ print $2 }'`
>  
>  	# Accounting here for the fact that the chosen subsystems could
>  	# have been already previously mounted at boot time: in such a
> @@ -267,10 +269,16 @@ test5()
>  	if [ -z "$mounted" ]; then
>  		mntpoint=cgroup
>  		failing=$subsys1
> -		mount -t cgroup -o $subsys1,$subsys2 xxx $mntpoint/
> +		mount -t cgroup -o $subsys1,$subsys2 xxx $mntpoint/ 2>/dev/null
> +		# Even subsystem has not been mounted, it still live in kernel.
> +		# So we will get EBUSY when both mount subsys1 and subsys2 if
> +		# hierarchy isn't equal to 0.
>  		if [ $? -ne 0 ]; then
> -			tst_res TFAIL "mount $subsys1 and $subsys2 failed"
> -			return
> +			if [ "$subsys1_hierarchy" = 0 -a "$subsys2_hierarchy" = 0 ]; then
> +				tst_res TFAIL "mount $subsys1 and $subsys2 failed"
> +				return
> +			fi
> +			failing=$subsys1,$subsys2
>  		fi
>  	else
>  		# Use the pre-esistent mountpoint as $mntpoint and use a