On 29.09.2020 16:55, Andrey Ryabinin wrote:
> Add update_rq_clock() for 'target_rq' to avoid WARN() coming
> from attach_task(). Also add update_rq_clock(env.src_rq); in
> load_balance() for detach_task().
> 
> https://jira.sw.ru/browse/PSBM-108013
> Reported-by: Kirill Tkhai <ktk...@virtuozzo.com>
> Signed-off-by: Andrey Ryabinin <aryabi...@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 e6dc21d5fa03..99dcb9e77efd 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7817,6 +7817,7 @@ static int cpulimit_balance_cpu_stop(void *data)
>               schedstat_inc(sd->clb_count);
>  
>               update_rq_clock(rq);
> +             update_rq_clock(target_rq);
>               if (do_cpulimit_balance(&env))
>                       schedstat_inc(sd->clb_pushed);
>               else
> @@ -9177,6 +9178,7 @@ 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.src_rq);

Fortunately, we may avoid update_rq_clock here, since srq_rq clock are already 
updated.
Also, I'm afraid this will bring to SCHED_WARN_ON(rq->clock_update_flags & 
RQCF_UPDATED)
in this function. It looks we should use rq_repin_lock() here instead:

@@ -9177,6 +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);
+                       rq_repin_lock(rq, &rf);
                        update_rq_clock(env.dst_rq);
                        cur_ld_moved = ld_moved = move_task_groups(&env);
                        double_rq_unlock(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);
> 

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