[PATCH-cgroup 2/5] cgroup/cpuset: Clear effective_xcpus on cpus_allowed clearing only if cpus.exclusive not set

[Waiman Long <longman@redhat.com>]

Commit e2ffe502ba45 ("cgroup/cpuset: Add cpuset.cpus.exclusive for
v2") adds a user writable cpuset.cpus.exclusive file for setting
exclusive CPUs to be used for the creation of partitions. Since then
effective_xcpus depends on both the cpuset.cpus and cpuset.cpus.exclusive
setting. If cpuset.cpus.exclusive is set, effective_xcpus will depend
only on cpuset.cpus.exclusive.  When it is not set, effective_xcpus
will be set according to the cpuset.cpus value when the cpuset becomes
a valid partition root.

When cpuset.cpus is being cleared by the user, effective_xcpus should
only be cleared when cpuset.cpus.exclusive is not set. However, that
is not currently the case.

  # cd /sys/fs/cgroup/
  # mkdir test
  # echo +cpuset > cgroup.subtree_control
  # cd test
  # echo 3 > cpuset.cpus.exclusive
  # cat cpuset.cpus.exclusive.effective
  3
  # echo > cpuset.cpus
  # cat cpuset.cpus.exclusive.effective // was cleared

Fix it by clearing effective_xcpus only if cpuset.cpus.exclusive is
not set.

Fixes: e2ffe502ba45 ("cgroup/cpuset: Add cpuset.cpus.exclusive for v2")
Reported-by: Chen Ridong <chenridong@huawei.com>
Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/cgroup/cpuset.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index f1846a08e245..7287cecb27d1 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2508,7 +2508,8 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
 	 */
 	if (!*buf) {
 		cpumask_clear(trialcs->cpus_allowed);
-		cpumask_clear(trialcs->effective_xcpus);
+		if (cpumask_empty(trialcs->exclusive_cpus))
+			cpumask_clear(trialcs->effective_xcpus);
 	} else {
 		retval = cpulist_parse(buf, trialcs->cpus_allowed);
 		if (retval < 0)
-- 
2.43.5