[PATCH] cpuset: Enforce that a child's cpus must be a subset of the parent

Waiman Long
2018-05-30T13:46:31Z

It was found that the cpuset.cpus could contain CPUs that are not listed
in their parent's cpu list as shown by the command sequence below:

# echo "+cpuset" >cgroup.subtree_control
# mkdir g1
# echo 0-5 >g1/cpuset.cpus
# mkdir g1/g11
# echo "+cpuset" > g1/cgroup.subtree_control
# echo 6-11 >g1/g11/cpuset.cpus
# grep -R . g1 | grep "\.cpus"
g1/cpuset.cpus:0-5
g1/cpuset.cpus.effective:0-5
g1/g11/cpuset.cpus:6-11
g1/g11/cpuset.cpus.effective:0-5

As the intersection of g11's cpus and that of g1 is empty, the effective
cpus of g11 is just that of g1. The check in update_cpumask() is now
corrected to make sure that cpus in a child cpus must be a subset of
its parent's cpus. The error "write error: Invalid argument" will now
be reported in the above case.

Reported-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/cgroup/cpuset.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 71fb2d0..ceec438 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1185,12 +1185,17 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
if (!*buf) {
cpumask_clear(trialcs->cpus_allowed);
} else {
+ struct cpuset *parent = parent_cs(cs);
+
retval = cpulist_parse(buf, trialcs->cpus_allowed);
if (retval < 0)
return retval;

+ /*
+ * The cpu list must be a subset of the parent.
+ */
if (!cpumask_subset(trialcs->cpus_allowed,
- top_cpuset.cpus_allowed))
+ parent->cpus_allowed))
return -EINVAL;
}

--
1.8.3.1