sched/fair: Disable runtime_enabled on dying rq

We kill rq->rd on the CPU_DOWN_PREPARE stage:

	cpuset_cpu_inactive -> cpuset_update_active_cpus -> partition_sched_domains ->
	-> cpu_attach_domain -> rq_attach_root -> set_rq_offline

This unthrottles all throttled cfs_rqs.

But the cpu is still able to call schedule() till

	take_cpu_down->__cpu_disable()

is called from stop_machine.

This case the tasks from just unthrottled cfs_rqs are pickable
in a standard scheduler way, and they are picked by dying cpu.
The cfs_rqs becomes throttled again, and migrate_tasks()
in migration_call skips their tasks (one more unthrottle
in migrate_tasks()->CPU_DYING does not happen, because rq->rd
is already NULL).

Patch sets runtime_enabled to zero. This guarantees, the runtime
is not accounted, and the cfs_rqs won't exceed given
cfs_rq->runtime_remaining = 1, and tasks will be pickable
in migrate_tasks(). runtime_enabled is recalculated again
when rq becomes online again.

Ben Segall also noticed, we always enable runtime in
tg_set_cfs_bandwidth(). Actually, we should do that for online
cpus only. To prevent races with unthrottle_offline_cfs_rqs()
we take get_online_cpus() lock.

Reviewed-by: Ben Segall <bsegall@google.com>
Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
CC: Konstantin Khorenko <khorenko@parallels.com>
CC: Paul Turner <pjt@google.com>
CC: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1403684382.3462.42.camel@tkhai
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e50234ba0b27e3aaaf5f0669d1a7ea549f2274a1..2dbc63d1a847655150ed921717d5f7e001cc41e5 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7817,6 +7817,11 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
        if (period > max_cfs_quota_period)
                return -EINVAL;
 
+       /*
+        * Prevent race between setting of cfs_rq->runtime_enabled and
+        * unthrottle_offline_cfs_rqs().
+        */
+       get_online_cpus();
        mutex_lock(&cfs_constraints_mutex);
        ret = __cfs_schedulable(tg, period, quota);
        if (ret)
@@ -7842,7 +7847,7 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
        }
        raw_spin_unlock_irq(&cfs_b->lock);
 
-       for_each_possible_cpu(i) {
+       for_each_online_cpu(i) {
                struct cfs_rq *cfs_rq = tg->cfs_rq[i];
                struct rq *rq = cfs_rq->rq;
 
@@ -7858,6 +7863,7 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
                cfs_bandwidth_usage_dec();
 out_unlock:
        mutex_unlock(&cfs_constraints_mutex);
+       put_online_cpus();
 
        return ret;
 }

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a140c6a8c9477f20b8251eedba287290ac7bddb5..923fe32db6b363a7b71d36c3642b48c07e2b3c76 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3798,6 +3798,19 @@ static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
        hrtimer_cancel(&cfs_b->slack_timer);
 }
 
+static void __maybe_unused update_runtime_enabled(struct rq *rq)
+{
+       struct cfs_rq *cfs_rq;
+
+       for_each_leaf_cfs_rq(rq, cfs_rq) {
+               struct cfs_bandwidth *cfs_b = &cfs_rq->tg->cfs_bandwidth;
+
+               raw_spin_lock(&cfs_b->lock);
+               cfs_rq->runtime_enabled = cfs_b->quota != RUNTIME_INF;
+               raw_spin_unlock(&cfs_b->lock);
+       }
+}
+
 static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
 {
        struct cfs_rq *cfs_rq;
@@ -3811,6 +3824,12 @@ static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
                 * there's some valid quota amount
                 */
                cfs_rq->runtime_remaining = 1;
+               /*
+                * Offline rq is schedulable till cpu is completely disabled
+                * in take_cpu_down(), so we prevent new cfs throttling here.
+                */
+               cfs_rq->runtime_enabled = 0;
+
                if (cfs_rq_throttled(cfs_rq))
                        unthrottle_cfs_rq(cfs_rq);
        }
@@ -3854,6 +3873,7 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
        return NULL;
 }
 static inline void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}
+static inline void update_runtime_enabled(struct rq *rq) {}
 static inline void unthrottle_offline_cfs_rqs(struct rq *rq) {}
 
 #endif /* CONFIG_CFS_BANDWIDTH */
@@ -7362,6 +7382,8 @@ void trigger_load_balance(struct rq *rq)
 static void rq_online_fair(struct rq *rq)
 {
        update_sysctl();
+
+       update_runtime_enabled(rq);
 }
 
 static void rq_offline_fair(struct rq *rq)