cgroup/cpuset: Fail if isolated and nohz_full don't leave any housekeeping

Currently the user can set up isolated cpus via cpuset and nohz_full in
such a way that leaves no housekeeping CPU (i.e. no CPU that is neither
domain isolated nor nohz full). This can be a problem for other
subsystems (e.g. the timer wheel imgration).

Prevent this configuration by blocking any assignation that would cause
the union of domain isolated cpus and nohz_full to covers all CPUs.

[longman: Remove isolated_cpus_should_update() and rewrite the checking
 in update_prstate() and update_parent_effective_cpumask()]

Originally-by: Gabriele Monaco <gmonaco@redhat.com>
Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Chen Ridong <chenridong@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index da770dac955edb837032c88d1c98a064f5b5446d..99622e90991a743718c332d92a02ed7e285b2f6f 100644 (file)
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1393,6 +1393,45 @@ static bool partition_xcpus_del(int old_prs, struct cpuset *parent,
        return isolcpus_updated;
 }
 
+/*
+ * isolated_cpus_can_update - check for isolated & nohz_full conflicts
+ * @add_cpus: cpu mask for cpus that are going to be isolated
+ * @del_cpus: cpu mask for cpus that are no longer isolated, can be NULL
+ * Return: false if there is conflict, true otherwise
+ *
+ * If nohz_full is enabled and we have isolated CPUs, their combination must
+ * still leave housekeeping CPUs.
+ *
+ * TBD: Should consider merging this function into
+ *      prstate_housekeeping_conflict().
+ */
+static bool isolated_cpus_can_update(struct cpumask *add_cpus,
+                                    struct cpumask *del_cpus)
+{
+       cpumask_var_t full_hk_cpus;
+       int res = true;
+
+       if (!housekeeping_enabled(HK_TYPE_KERNEL_NOISE))
+               return true;
+
+       if (del_cpus && cpumask_weight_and(del_cpus,
+                       housekeeping_cpumask(HK_TYPE_KERNEL_NOISE)))
+               return true;
+
+       if (!alloc_cpumask_var(&full_hk_cpus, GFP_KERNEL))
+               return false;
+
+       cpumask_and(full_hk_cpus, housekeeping_cpumask(HK_TYPE_KERNEL_NOISE),
+                   housekeeping_cpumask(HK_TYPE_DOMAIN));
+       cpumask_andnot(full_hk_cpus, full_hk_cpus, isolated_cpus);
+       cpumask_and(full_hk_cpus, full_hk_cpus, cpu_active_mask);
+       if (!cpumask_weight_andnot(full_hk_cpus, add_cpus))
+               res = false;
+
+       free_cpumask_var(full_hk_cpus);
+       return res;
+}
+
 static void update_isolation_cpumasks(bool isolcpus_updated)
 {
        int ret;
@@ -1551,6 +1590,9 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs,
        if (!cpumask_intersects(tmp->new_cpus, cpu_active_mask) ||
            cpumask_subset(top_cpuset.effective_cpus, tmp->new_cpus))
                return PERR_INVCPUS;
+       if ((new_prs == PRS_ISOLATED) &&
+           !isolated_cpus_can_update(tmp->new_cpus, NULL))
+               return PERR_HKEEPING;
 
        spin_lock_irq(&callback_lock);
        isolcpus_updated = partition_xcpus_add(new_prs, NULL, tmp->new_cpus);
@@ -1650,6 +1692,9 @@ static void remote_cpus_update(struct cpuset *cs, struct cpumask *xcpus,
                else if (cpumask_intersects(tmp->addmask, subpartitions_cpus) ||
                         cpumask_subset(top_cpuset.effective_cpus, tmp->addmask))
                        cs->prs_err = PERR_NOCPUS;
+               else if ((prs == PRS_ISOLATED) &&
+                        !isolated_cpus_can_update(tmp->addmask, tmp->delmask))
+                       cs->prs_err = PERR_HKEEPING;
                if (cs->prs_err)
                        goto invalidate;
        }
@@ -1750,6 +1795,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
        int part_error = PERR_NONE;     /* Partition error? */
        int isolcpus_updated = 0;
        struct cpumask *xcpus = user_xcpus(cs);
+       int parent_prs = parent->partition_root_state;
        bool nocpu;
 
        lockdep_assert_held(&cpuset_mutex);
@@ -1813,6 +1859,10 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
                if (prstate_housekeeping_conflict(new_prs, xcpus))
                        return PERR_HKEEPING;
 
+               if ((new_prs == PRS_ISOLATED) && (new_prs != parent_prs) &&
+                   !isolated_cpus_can_update(xcpus, NULL))
+                       return PERR_HKEEPING;
+
                if (tasks_nocpu_error(parent, cs, xcpus))
                        return PERR_NOCPUS;
 
@@ -1866,6 +1916,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
                 *
                 * For invalid partition:
                 *   delmask = newmask & parent->effective_xcpus
+                *   The partition may become valid soon.
                 */
                if (is_partition_invalid(cs)) {
                        adding = false;
@@ -1880,6 +1931,23 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
                        deleting = cpumask_and(tmp->delmask, tmp->delmask,
                                               parent->effective_xcpus);
                }
+
+               /*
+                * TBD: Invalidate a currently valid child root partition may
+                * still break isolated_cpus_can_update() rule if parent is an
+                * isolated partition.
+                */
+               if (is_partition_valid(cs) && (old_prs != parent_prs)) {
+                       if ((parent_prs == PRS_ROOT) &&
+                           /* Adding to parent means removing isolated CPUs */
+                           !isolated_cpus_can_update(tmp->delmask, tmp->addmask))
+                               part_error = PERR_HKEEPING;
+                       if ((parent_prs == PRS_ISOLATED) &&
+                           /* Adding to parent means adding isolated CPUs */
+                           !isolated_cpus_can_update(tmp->addmask, tmp->delmask))
+                               part_error = PERR_HKEEPING;
+               }
+
                /*
                 * The new CPUs to be removed from parent's effective CPUs
                 * must be present.
@@ -2994,7 +3062,11 @@ static int update_prstate(struct cpuset *cs, int new_prs)
                 * A change in load balance state only, no change in cpumasks.
                 * Need to update isolated_cpus.
                 */
-               isolcpus_updated = true;
+               if ((new_prs == PRS_ISOLATED) &&
+                   !isolated_cpus_can_update(cs->effective_xcpus, NULL))
+                       err = PERR_HKEEPING;
+               else
+                       isolcpus_updated = true;
        } else {
                /*
                 * Switching back to member is always allowed even if it