1 files changed, 47 insertions, 32 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 02f323b85b6d..0c13a41bde81 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4588,16 +4588,16 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
 }
 
 /* returns 0 on failure to allocate runtime */
-static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
+static int __assign_cfs_rq_runtime(struct cfs_bandwidth *cfs_b,
+				   struct cfs_rq *cfs_rq, u64 target_runtime)
 {
-	struct task_group *tg = cfs_rq->tg;
-	struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(tg);
-	u64 amount = 0, min_amount;
+	u64 min_amount, amount = 0;
+
+	lockdep_assert_held(&cfs_b->lock);
 
 	/* note: this is a positive sum as runtime_remaining <= 0 */
-	min_amount = sched_cfs_bandwidth_slice() - cfs_rq->runtime_remaining;
+	min_amount = target_runtime - cfs_rq->runtime_remaining;
 
-	raw_spin_lock(&cfs_b->lock);
 	if (cfs_b->quota == RUNTIME_INF)
 		amount = min_amount;
 	else {
@@ -4609,13 +4609,25 @@ static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
 			cfs_b->idle = 0;
 		}
 	}
-	raw_spin_unlock(&cfs_b->lock);
 
 	cfs_rq->runtime_remaining += amount;
 
 	return cfs_rq->runtime_remaining > 0;
 }
 
+/* returns 0 on failure to allocate runtime */
+static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
+{
+	struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
+	int ret;
+
+	raw_spin_lock(&cfs_b->lock);
+	ret = __assign_cfs_rq_runtime(cfs_b, cfs_rq, sched_cfs_bandwidth_slice());
+	raw_spin_unlock(&cfs_b->lock);
+
+	return ret;
+}
+
 static void __account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
 {
 	/* dock delta_exec before expiring quota (as it could span periods) */
@@ -4704,13 +4716,33 @@ static int tg_throttle_down(struct task_group *tg, void *data)
 	return 0;
 }
 
-static void throttle_cfs_rq(struct cfs_rq *cfs_rq)
+static bool throttle_cfs_rq(struct cfs_rq *cfs_rq)
 {
 	struct rq *rq = rq_of(cfs_rq);
 	struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
 	struct sched_entity *se;
 	long task_delta, idle_task_delta, dequeue = 1;
-	bool empty;
+
+	raw_spin_lock(&cfs_b->lock);
+	/* This will start the period timer if necessary */
+	if (__assign_cfs_rq_runtime(cfs_b, cfs_rq, 1)) {
+		/*
+		 * We have raced with bandwidth becoming available, and if we
+		 * actually throttled the timer might not unthrottle us for an
+		 * entire period. We additionally needed to make sure that any
+		 * subsequent check_cfs_rq_runtime calls agree not to throttle
+		 * us, as we may commit to do cfs put_prev+pick_next, so we ask
+		 * for 1ns of runtime rather than just check cfs_b.
+		 */
+		dequeue = 0;
+	} else {
+		list_add_tail_rcu(&cfs_rq->throttled_list,
+				  &cfs_b->throttled_cfs_rq);
+	}
+	raw_spin_unlock(&cfs_b->lock);
+
+	if (!dequeue)
+		return false;  /* Throttle no longer required. */
 
 	se = cfs_rq->tg->se[cpu_of(rq_of(cfs_rq))];
 
@@ -4744,29 +4776,13 @@ static void throttle_cfs_rq(struct cfs_rq *cfs_rq)
 	if (!se)
 		sub_nr_running(rq, task_delta);
 
-	cfs_rq->throttled = 1;
-	cfs_rq->throttled_clock = rq_clock(rq);
-	raw_spin_lock(&cfs_b->lock);
-	empty = list_empty(&cfs_b->throttled_cfs_rq);
-
-	/*
-	 * Add to the _head_ of the list, so that an already-started
-	 * distribute_cfs_runtime will not see us. If disribute_cfs_runtime is
-	 * not running add to the tail so that later runqueues don't get starved.
-	 */
-	if (cfs_b->distribute_running)
-		list_add_rcu(&cfs_rq->throttled_list, &cfs_b->throttled_cfs_rq);
-	else
-		list_add_tail_rcu(&cfs_rq->throttled_list, &cfs_b->throttled_cfs_rq);
-
 	/*
-	 * If we're the first throttled task, make sure the bandwidth
-	 * timer is running.
+	 * Note: distribution will already see us throttled via the
+	 * throttled-list.  rq->lock protects completion.
 	 */
-	if (empty)
-		start_cfs_bandwidth(cfs_b);
-
-	raw_spin_unlock(&cfs_b->lock);
+	cfs_rq->throttled = 1;
+	cfs_rq->throttled_clock = rq_clock(rq);
+	return true;
 }
 
 void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
@@ -5121,8 +5137,7 @@ static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq)
 	if (cfs_rq_throttled(cfs_rq))
 		return true;
 
-	throttle_cfs_rq(cfs_rq);
-	return true;
+	return throttle_cfs_rq(cfs_rq);
 }
 
 static enum hrtimer_restart sched_cfs_slack_timer(struct hrtimer *timer)