cgroup/cpuset: Add warnings to catch inconsistency in exclusive CPUs

Add WARN_ON_ONCE() statements whenever new exclusive CPUs are being
added to a partition root to catch inconsistency in the way exclusive
CPUs are being handled in the cpuset code.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 1497a2a4b2a35e1071a44ca46028adf109f3da02..d0143b3dce47e0c3cabdfe8210e794c25ba272b5 100644 (file)
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1453,13 +1453,15 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs,
         * The requested exclusive_cpus must not be allocated to other
         * partitions and it can't use up all the root's effective_cpus.
         *
-        * Note that if there is any local partition root above it or
-        * remote partition root underneath it, its exclusive_cpus must
-        * have overlapped with subpartitions_cpus.
+        * The effective_xcpus mask can contain offline CPUs, but there must
+        * be at least one or more online CPUs present before it can be enabled.
+        *
+        * Note that creating a remote partition with any local partition root
+        * above it or remote partition root underneath it is not allowed.
         */
        compute_effective_exclusive_cpumask(cs, tmp->new_cpus, NULL);
-       if (cpumask_empty(tmp->new_cpus) ||
-           cpumask_intersects(tmp->new_cpus, subpartitions_cpus) ||
+       WARN_ON_ONCE(cpumask_intersects(tmp->new_cpus, subpartitions_cpus));
+       if (!cpumask_intersects(tmp->new_cpus, cpu_active_mask) ||
            cpumask_subset(top_cpuset.effective_cpus, tmp->new_cpus))
                return PERR_INVCPUS;
 
@@ -1555,6 +1557,7 @@ static void remote_cpus_update(struct cpuset *cs, struct cpumask *xcpus,
         * left in the top cpuset.
         */
        if (adding) {
+               WARN_ON_ONCE(cpumask_intersects(tmp->addmask, subpartitions_cpus));
                if (!capable(CAP_SYS_ADMIN))
                        cs->prs_err = PERR_ACCESS;
                else if (cpumask_intersects(tmp->addmask, subpartitions_cpus) ||
@@ -1664,7 +1667,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
        bool nocpu;
 
        lockdep_assert_held(&cpuset_mutex);
-       WARN_ON_ONCE(is_remote_partition(cs));
+       WARN_ON_ONCE(is_remote_partition(cs));  /* For local partition only */
 
        /*
         * new_prs will only be changed for the partcmd_update and
@@ -1710,7 +1713,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
                 * exclusive_cpus not set. Sibling conflict should only happen
                 * if exclusive_cpus isn't set.
                 */
-               xcpus = tmp->new_cpus;
+               xcpus = tmp->delmask;
                if (compute_effective_exclusive_cpumask(cs, xcpus, NULL))
                        WARN_ON_ONCE(!cpumask_empty(cs->exclusive_cpus));
 
@@ -1731,9 +1734,20 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
                if (nocpu)
                        return PERR_NOCPUS;
 
-               deleting = cpumask_and(tmp->delmask, xcpus, parent->effective_xcpus);
-               if (deleting)
-                       subparts_delta++;
+               /*
+                * This function will only be called when all the preliminary
+                * checks have passed. At this point, the following condition
+                * should hold.
+                *
+                * (cs->effective_xcpus & cpu_active_mask) ⊆ parent->effective_cpus
+                *
+                * Warn if it is not the case.
+                */
+               cpumask_and(tmp->new_cpus, xcpus, cpu_active_mask);
+               WARN_ON_ONCE(!cpumask_subset(tmp->new_cpus, parent->effective_cpus));
+
+               deleting = true;
+               subparts_delta++;
                new_prs = (cmd == partcmd_enable) ? PRS_ROOT : PRS_ISOLATED;
        } else if (cmd == partcmd_disable) {
                /*
@@ -1787,6 +1801,15 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
                        deleting = cpumask_and(tmp->delmask, tmp->delmask,
                                               parent->effective_xcpus);
                }
+               /*
+                * The new CPUs to be removed from parent's effective CPUs
+                * must be present.
+                */
+               if (deleting) {
+                       cpumask_and(tmp->new_cpus, tmp->delmask, cpu_active_mask);
+                       WARN_ON_ONCE(!cpumask_subset(tmp->new_cpus, parent->effective_cpus));
+               }
+
                /*
                 * Make partition invalid if parent's effective_cpus could
                 * become empty and there are tasks in the parent.