linux-yocto/5.10: cgroup1: fix leaked context root causing sporadic NULL deref in LTP

Integrating the following commit(s) to linux-yocto/5.10:

    ab49d2db98bd cgroup1: fix leaked context root causing sporadic NULL deref in LTP

PaulG tracked down the AB intermittent issues and generated a kernel
patch.

See: https://lore.kernel.org/lkml/20210616125157.438837-1-paul.gortmaker@windriver.com/



While we wait for it to loop through mainline, we'll integrate it into
our 5.10 branches.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 9a16dff7)
Signed-off-by: Anuj Mittal <anuj.mittal@intel.com>