[Devel] [PATCH RHEL8 COMMIT] kernel/sched/fair.c: Add missing update_rq_clock() calls

[Konstantin Khorenko]

The commit is pushed to "branch-rh8-4.18.0-193.6.3.vz8.4.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-193.6.3.vz8.4.9
------>
commit 15645110b30affdf50f83b458724c8b503224aa4
Author: Andrey Ryabinin <aryabinin at virtuozzo.com>
Date:   Mon Sep 28 18:46:06 2020 +0300

    kernel/sched/fair.c: Add missing update_rq_clock() calls
    
    We've got a hard lockup which seems to be caused by mgag200
    console printk code calling to schedule_work from scheduler
    with rq->lock held:
    
     #5 [ffffb79e034239a8] native_queued_spin_lock_slowpath at ffffffff8b50c6c6
     #6 [ffffb79e034239a8] _raw_spin_lock at ffffffff8bc96e5c
     #7 [ffffb79e034239b0] try_to_wake_up at ffffffff8b4e26ff
     #8 [ffffb79e03423a10] __queue_work at ffffffff8b4ce3f3
     #9 [ffffb79e03423a58] queue_work_on at ffffffff8b4ce714
    
    The printk called because assert_clock_updated() triggered
            SCHED_WARN_ON(rq->clock_update_flags < RQCF_ACT_SKIP);
    
    This means that we missing necessary update_rq_clock() call.
    Add one to cpulimit_balance_cpu_stop() to fix the warning.
    Also add one in load_balance() before move_task_groups() call.
    It seems to be another place missing this call.
    
    https://jira.sw.ru/browse/PSBM-108013
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 kernel/sched/fair.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5d3556b15e70..e6dc21d5fa03 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7816,6 +7816,7 @@ static int cpulimit_balance_cpu_stop(void *data)
 
 		schedstat_inc(sd->clb_count);
 
+		update_rq_clock(rq);
 		if (do_cpulimit_balance(&env))
 			schedstat_inc(sd->clb_pushed);
 		else
@@ -9176,6 +9177,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
 			env.loop = 0;
 			local_irq_save(rf.flags);
 			double_rq_lock(env.dst_rq, busiest);
+			update_rq_clock(env.dst_rq);
 			cur_ld_moved = ld_moved = move_task_groups(&env);
 			double_rq_unlock(env.dst_rq, busiest);
 			local_irq_restore(rf.flags);