Re: [PATCH] cgroup/cpuset: Fix wrong check in update_parent_subparts_cpumask()

[Tejun Heo <tj@kernel.org>]

On Tue, Jan 31, 2023 at 10:48:03AM -0500, Waiman Long wrote:
> 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")
> Reported-by: Srinivas Pandruvada <srinivas.pandruvada@intel.com>
> Signed-off-by: Waiman Long <longman@redhat.com>

Applied to cgroup/for-6.2-fixes w/ stable cc added.

Thanks.

-- 
tejun