1 files changed, 74 insertions, 59 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index f8b8996228dd..cb816e36cc8b 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -306,52 +306,6 @@ static int init_task_group_load = INIT_TASK_GROUP_LOAD;
  */
 struct task_group init_task_group;
 
-/* return group to which a task belongs */
-static inline struct task_group *task_group(struct task_struct *p)
-{
-        struct task_group *tg;
-
-#ifdef CONFIG_CGROUP_SCHED
-        tg = container_of(task_subsys_state(p, cpu_cgroup_subsys_id),
-                                struct task_group, css);
-#else
-        tg = &init_task_group;
-#endif
-        return tg;
-}
-
-/* Change a task's cfs_rq and parent entity if it moves across CPUs/groups */
-static inline void set_task_rq(struct task_struct *p, unsigned int cpu)
-{
-        /*
-         * Strictly speaking this rcu_read_lock() is not needed since the
-         * task_group is tied to the cgroup, which in turn can never go away
-         * as long as there are tasks attached to it.
-         *
-         * However since task_group() uses task_subsys_state() which is an
-         * rcu_dereference() user, this quiets CONFIG_PROVE_RCU.
-         */
-        rcu_read_lock();
-#ifdef CONFIG_FAIR_GROUP_SCHED
-        p->se.cfs_rq = task_group(p)->cfs_rq[cpu];
-        p->se.parent = task_group(p)->se[cpu];
-#endif
-
-#ifdef CONFIG_RT_GROUP_SCHED
-        p->rt.rt_rq  = task_group(p)->rt_rq[cpu];
-        p->rt.parent = task_group(p)->rt_se[cpu];
-#endif
-        rcu_read_unlock();
-}
-
-#else
-
-static inline void set_task_rq(struct task_struct *p, unsigned int cpu) { }
-static inline struct task_group *task_group(struct task_struct *p)
-{
-        return NULL;
-}
-
 #endif  /* CONFIG_CGROUP_SCHED */
 
 /* CFS-related fields in a runqueue */
@@ -644,6 +598,49 @@ static inline int cpu_of(struct rq *rq)
 #define cpu_curr(cpu)           (cpu_rq(cpu)->curr)
 #define raw_rq()                (&__raw_get_cpu_var(runqueues))
 
+#ifdef CONFIG_CGROUP_SCHED
+
+/*
+ * Return the group to which this tasks belongs.
+ *
+ * We use task_subsys_state_check() and extend the RCU verification
+ * with lockdep_is_held(&task_rq(p)->lock) because cpu_cgroup_attach()
+ * holds that lock for each task it moves into the cgroup. Therefore
+ * by holding that lock, we pin the task to the current cgroup.
+ */
+static inline struct task_group *task_group(struct task_struct *p)
+{
+        struct cgroup_subsys_state *css;
+
+        css = task_subsys_state_check(p, cpu_cgroup_subsys_id,
+                        lockdep_is_held(&task_rq(p)->lock));
+        return container_of(css, struct task_group, css);
+}
+
+/* Change a task's cfs_rq and parent entity if it moves across CPUs/groups */
+static inline void set_task_rq(struct task_struct *p, unsigned int cpu)
+{
+#ifdef CONFIG_FAIR_GROUP_SCHED
+        p->se.cfs_rq = task_group(p)->cfs_rq[cpu];
+        p->se.parent = task_group(p)->se[cpu];
+#endif
+
+#ifdef CONFIG_RT_GROUP_SCHED
+        p->rt.rt_rq  = task_group(p)->rt_rq[cpu];
+        p->rt.parent = task_group(p)->rt_se[cpu];
+#endif
+}
+
+#else /* CONFIG_CGROUP_SCHED */
+
+static inline void set_task_rq(struct task_struct *p, unsigned int cpu) { }
+static inline struct task_group *task_group(struct task_struct *p)
+{
+        return NULL;
+}
+
+#endif /* CONFIG_CGROUP_SCHED */
+
 inline void update_rq_clock(struct rq *rq)
 {
         if (!rq->skip_clock_update)
@@ -1257,6 +1254,12 @@ static void sched_avg_update(struct rq *rq)
         s64 period = sched_avg_period();
 
         while ((s64)(rq->clock - rq->age_stamp) > period) {
+                /*
+                 * Inline assembly required to prevent the compiler
+                 * optimising this loop into a divmod call.
+                 * See __iter_div_u64_rem() for another example of this.
+                 */
+                asm("" : "+rm" (rq->age_stamp));
                 rq->age_stamp += period;
                 rq->rt_avg /= 2;
         }
@@ -1660,9 +1663,6 @@ static void update_shares(struct sched_domain *sd)
 
 static void update_h_load(long cpu)
 {
-        if (root_task_group_empty())
-                return;
-
         walk_tg_tree(tg_load_down, tg_nop, (void *)cpu);
 }
 
@@ -2494,7 +2494,16 @@ void sched_fork(struct task_struct *p, int clone_flags)
         if (p->sched_class->task_fork)
                 p->sched_class->task_fork(p);
 
+        /*
+         * The child is not yet in the pid-hash so no cgroup attach races,
+         * and the cgroup is pinned to this child due to cgroup_fork()
+         * is ran before sched_fork().
+         *
+         * Silence PROVE_RCU.
+         */
+        rcu_read_lock();
         set_task_cpu(p, cpu);
+        rcu_read_unlock();
 
 #if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
         if (likely(sched_info_on()))
@@ -4465,16 +4474,6 @@ recheck:
         }
 
         if (user) {
-#ifdef CONFIG_RT_GROUP_SCHED
-                /*
-                 * Do not allow realtime tasks into groups that have no runtime
-                 * assigned.
-                 */
-                if (rt_bandwidth_enabled() && rt_policy(policy) &&
-                                task_group(p)->rt_bandwidth.rt_runtime == 0)
-                        return -EPERM;
-#endif
-
                 retval = security_task_setscheduler(p, policy, param);
                 if (retval)
                         return retval;
@@ -4490,6 +4489,22 @@ recheck:
          * runqueue lock must be held.
          */
         rq = __task_rq_lock(p);
+
+#ifdef CONFIG_RT_GROUP_SCHED
+        if (user) {
+                /*
+                 * Do not allow realtime tasks into groups that have no runtime
+                 * assigned.
+                 */
+                if (rt_bandwidth_enabled() && rt_policy(policy) &&
+                                task_group(p)->rt_bandwidth.rt_runtime == 0) {
+                        __task_rq_unlock(rq);
+                        raw_spin_unlock_irqrestore(&p->pi_lock, flags);
+                        return -EPERM;
+                }
+        }
+#endif
+
         /* recheck policy now with rq lock held */
         if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) {
                 policy = oldpolicy = -1;