!1280 cgroup: always put cset in cgroup_css_set_put_fork

Merge Pull Request from: @wufan618223 
 
    A successful call to cgroup_css_set_fork() will always have taken
    a ref on kargs->cset (regardless of CLONE_INTO_CGROUP), so always
    do a corresponding put in cgroup_css_set_put_fork().

    Without this, a cset and its contained css structures will be
    leaked for some fork failures.  The following script reproduces
    the leak for a fork failure due to exceeding pids.max in the
    pids controller.  A similar thing can happen if we jump to the
    bad_fork_cancel_cgroup label in copy_process().

    [ -z "$1" ] && echo "Usage $0 pids-root" && exit 1
    PID_ROOT=$1
    CGROUP=$PID_ROOT/foo

    [ -e $CGROUP ] && rmdir -f $CGROUP
    mkdir $CGROUP
    echo 5 > $CGROUP/pids.max
    echo $$ > $CGROUP/cgroup.procs

    fork_bomb()
    {
            set -e
            for i in $(seq 10); do
                    /bin/sleep 3600 &
            done
    }

    (fork_bomb) &
    wait
    echo $$ > $PID_ROOT/cgroup.procs
    kill $(cat $CGROUP/cgroup.procs)
    rmdir $CGROUP 
 
Link:https://gitee.com/openeuler/kernel/pulls/1280

 

Reviewed-by: Jialin Zhang <zhangjialin11@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>