[PATCH 2/2] sched/core: Avoid double calling update_rq_clock()

[Hao Jia]

There are some double rq clock update warnings are triggered.
------------[ cut here ]------------
rq->clock_update_flags & RQCF_UPDATED
WARNING: CPU: 17 PID: 138 at kernel/sched/core.c:741
update_rq_clock+0xaf/0x180
Call Trace:
 <TASK>
 __balance_push_cpu_stop+0x146/0x180
 ? migration_cpu_stop+0x2a0/0x2a0
 cpu_stopper_thread+0xa3/0x140
 smpboot_thread_fn+0x14f/0x210
 ? sort_range+0x20/0x20
 kthread+0xe6/0x110
 ? kthread_complete_and_exit+0x20/0x20
 ret_from_fork+0x1f/0x30

------------[ cut here ]------------
rq->clock_update_flags & RQCF_UPDATED
WARNING: CPU: 54 PID: 0 at kernel/sched/core.c:741
update_rq_clock+0xaf/0x180
Call Trace:
 <TASK>
 unthrottle_cfs_rq+0x4b/0x300
 __cfsb_csd_unthrottle+0xe0/0x100
 __flush_smp_call_function_queue+0xaf/0x1d0
 flush_smp_call_function_queue+0x49/0x90
 do_idle+0x17c/0x270
 cpu_startup_entry+0x19/0x20
 start_secondary+0xfa/0x120
 secondary_startup_64_no_verify+0xce/0xdb

------------[ cut here ]------------
rq->clock_update_flags & RQCF_UPDATED
WARNING: CPU: 0 PID: 3323 at kernel/sched/core.c:741
update_rq_clock+0xaf/0x180
Call Trace:
 <TASK>
 unthrottle_cfs_rq+0x4b/0x300
 rq_offline_fair+0x89/0x90
 set_rq_offline.part.118+0x28/0x60
 rq_attach_root+0xc4/0xd0
 cpu_attach_domain+0x3dc/0x7f0
 partition_sched_domains_locked+0x2a5/0x3c0
 rebuild_sched_domains_locked+0x477/0x830
 rebuild_sched_domains+0x1b/0x30
 cpuset_hotplug_workfn+0x2ca/0xc90
 ? balance_push+0x56/0xf0
 ? _raw_spin_unlock+0x15/0x30
 ? finish_task_switch+0x98/0x2f0
 ? __switch_to+0x291/0x410
 ? __schedule+0x65e/0x1310
 process_one_work+0x1bc/0x3d0
 worker_thread+0x4c/0x380
 ? preempt_count_add+0x92/0xa0
 ? rescuer_thread+0x310/0x310
 kthread+0xe6/0x110
 ? kthread_complete_and_exit+0x20/0x20
 ret_from_fork+0x1f/0x30

For the __balance_push_cpu_stop() case, we remove update_rq_clock() from
the __migrate_task() function to avoid double updating the rq clock.
And in order to avoid missing rq clock update, add update_rq_clock()
call before migration_cpu_stop() calls __migrate_task().

This also works for unthrottle_cfs_rq(), so we also removed
update_rq_clock() from the unthrottle_cfs_rq() function to avoid
warnings caused by calling it multiple times, such as
__cfsb_csd_unthrottle() and unthrottle_offline_cfs_rqs(). and
in order to avoid missing rq clock update, we correspondingly add
update_rq_clock() calls before unthrottle_cfs_rq() runs.

Note that the rq clock has been updated before the set_rq_offline()
function runs, so we don't need to add update_rq_clock() call in
unthrottle_offline_cfs_rqs().

Signed-off-by: Hao Jia <jiahao.os@xxxxxxxxxxxxx>
---
 kernel/sched/core.c | 11 +++++++----
 kernel/sched/fair.c |  9 ++++++---
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0d18c3969f90..c1abd88ec1ed 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2376,7 +2376,6 @@ static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
 	if (!is_cpu_allowed(p, dest_cpu))
 		return rq;
 
-	update_rq_clock(rq);
 	rq = move_queued_task(rq, rf, p, dest_cpu);
 
 	return rq;
@@ -2434,10 +2433,12 @@ static int migration_cpu_stop(void *data)
 				goto out;
 		}
 
-		if (task_on_rq_queued(p))
+		if (task_on_rq_queued(p)) {
+			update_rq_clock(rq);
 			rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
-		else
+		} else {
 			p->wake_cpu = arg->dest_cpu;
+		}
 
 		/*
 		 * XXX __migrate_task() can fail, at which point we might end
@@ -10759,8 +10760,10 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota,
 		cfs_rq->runtime_enabled = runtime_enabled;
 		cfs_rq->runtime_remaining = 0;
 
-		if (cfs_rq->throttled)
+		if (cfs_rq->throttled) {
+			update_rq_clock(rq);
 			unthrottle_cfs_rq(cfs_rq);
+		}
 		rq_unlock_irq(rq, &rf);
 	}
 	if (runtime_was_enabled && !runtime_enabled)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6986ea31c984..03ced34e992e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5438,8 +5438,6 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
 
 	cfs_rq->throttled = 0;
 
-	update_rq_clock(rq);
-
 	raw_spin_lock(&cfs_b->lock);
 	cfs_b->throttled_time += rq_clock(rq) - cfs_rq->throttled_clock;
 	list_del_rcu(&cfs_rq->throttled_list);
@@ -5518,6 +5516,7 @@ static void __cfsb_csd_unthrottle(void *arg)
 	struct rq_flags rf;
 
 	rq_lock(rq, &rf);
+	update_rq_clock(rq);
 
 	/*
 	 * Since we hold rq lock we're safe from concurrent manipulation of
@@ -5547,6 +5546,7 @@ static inline void __unthrottle_cfs_rq_async(struct cfs_rq *cfs_rq)
 	bool first;
 
 	if (rq == this_rq()) {
+		update_rq_clock(rq);
 		unthrottle_cfs_rq(cfs_rq);
 		return;
 	}
@@ -5563,6 +5563,7 @@ static inline void __unthrottle_cfs_rq_async(struct cfs_rq *cfs_rq)
 #else
 static inline void __unthrottle_cfs_rq_async(struct cfs_rq *cfs_rq)
 {
+	update_rq_clock(rq_of(cfs_rq));
 	unthrottle_cfs_rq(cfs_rq);
 }
 #endif
@@ -5640,8 +5641,10 @@ static bool distribute_cfs_runtime(struct cfs_bandwidth *cfs_b)
 	if (local_unthrottle) {
 		rq = cpu_rq(this_cpu);
 		rq_lock_irqsave(rq, &rf);
-		if (cfs_rq_throttled(local_unthrottle))
+		if (cfs_rq_throttled(local_unthrottle)) {
+			update_rq_clock(rq);
 			unthrottle_cfs_rq(local_unthrottle);
+		}
 		rq_unlock_irqrestore(rq, &rf);
 	}
 
-- 
2.37.0