cgroup/cpuset: Fix wrong check in update_parent_subparts_cpumask()

It was found that the check to see if a partition could use up all
the cpus from the parent cpuset in update_parent_subparts_cpumask()
was incorrect. As a result, it is possible to leave parent with no
effective cpu left even if there are tasks in the parent cpuset. This
can lead to system panic as reported in [1].

Fix this probem by updating the check to fail the enabling the partition
if parent's effective_cpus is a subset of the child's cpus_allowed.

Also record the error code when an error happens in update_prstate()
and add a test case where parent partition and child have the same cpu
list and parent has task. Enabling partition in the child will fail in
this case.

[1] https://www.spinics.net/lists/cgroups/msg36254.html

Fixes: f0af1bfc27b5 ("cgroup/cpuset: Relax constraints to partition & cpus changes")
Cc: [email protected] # v6.1
Reported-by: Srinivas Pandruvada <[email protected]>
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>

0 files changed, 0 insertions, 0 deletions