[PATCH V4 18/38] x86/intel_rdt: Add utility to test if tasks assigned to resource group

[Reinette Chatre]

In considering changes to a resource group it becomes necessary to know
whether tasks have been assigned to the resource group in question.

Introduce a new utility that can be used to check if any tasks have been
assigned to a particular resource group.

Signed-off-by: Reinette Chatre <reinette.cha...@intel.com>
---
 arch/x86/kernel/cpu/intel_rdt.h          |  1 +
 arch/x86/kernel/cpu/intel_rdt_rdtgroup.c | 26 ++++++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/arch/x86/kernel/cpu/intel_rdt.h b/arch/x86/kernel/cpu/intel_rdt.h
index bda87f5ef7bc..10a1539cbec6 100644
--- a/arch/x86/kernel/cpu/intel_rdt.h
+++ b/arch/x86/kernel/cpu/intel_rdt.h
@@ -480,6 +480,7 @@ bool rdtgroup_cbm_overlaps(struct rdt_resource *r, struct 
rdt_domain *d,
 unsigned int rdtgroup_cbm_to_size(struct rdt_resource *r, struct rdt_domain *d,
                                  u32 cbm);
 enum rdtgrp_mode rdtgroup_mode_by_closid(int closid);
+int rdtgroup_tasks_assigned(struct rdtgroup *r);
 struct rdt_domain *get_domain_from_cpu(int cpu, struct rdt_resource *r);
 int update_domains(struct rdt_resource *r, int closid);
 void closid_free(int closid);
diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c 
b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
index 7d623d940e49..f431ab493339 100644
--- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
+++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
@@ -564,6 +564,32 @@ static int __rdtgroup_move_task(struct task_struct *tsk,
        return ret;
 }
 
+/**
+ * rdtgroup_tasks_assigned - Test if tasks have been assigned to resource group
+ * @r: Resource group
+ *
+ * Return: 1 if tasks have been assigned to @r, 0 otherwise
+ */
+int rdtgroup_tasks_assigned(struct rdtgroup *r)
+{
+       struct task_struct *p, *t;
+       int ret = 0;
+
+       lockdep_assert_held(&rdtgroup_mutex);
+
+       rcu_read_lock();
+       for_each_process_thread(p, t) {
+               if ((r->type == RDTCTRL_GROUP && t->closid == r->closid) ||
+                   (r->type == RDTMON_GROUP && t->rmid == r->mon.rmid)) {
+                       ret = 1;
+                       break;
+               }
+       }
+       rcu_read_unlock();
+
+       return ret;
+}
+
 static int rdtgroup_task_write_permission(struct task_struct *task,
                                          struct kernfs_open_file *of)
 {
-- 
2.13.6