Re: [PATCH] sched/core: Avoid WARN_DOUBLE_CLOCK warning when CONFIG_SCHED_CORE

[Hao Jia]

Friendly ping...

On 2022/12/6 Hao Jia wrote:
> When we need to call update_rq_clock() to update the rq clock of
> other CPUs on the same core, before that we need to clear RQCF_UPDATED
> of rq->clock_update_flags to avoid the WARN_DOUBLE_CLOCK warning.
> Because at this time the rq->clock_update_flags of other CPUs
> may be RQCF_UPDATED.
>
> Some call trace reports:
> Call Trace 1:
> <TASK>
> __schedule+0x61c/0x11d0
> schedule+0x5d/0xd0
> worker_thread+0xb5/0x380
> ? preempt_count_add+0x56/0xa0
> ? rescuer_thread+0x310/0x310
> kthread+0xe6/0x110
> ? kthread_complete_and_exit+0x20/0x20
> ret_from_fork+0x1f/0x30
> </TASK>
>
> Call Trace 2:
> <TASK>
> __schedule+0x91d/0x11d0
> schedule+0x5d/0xd0
> exit_to_user_mode_prepare+0xe5/0x1e0
> syscall_exit_to_user_mode+0x17/0x30
> do_syscall_64+0x40/0x90
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> Call Trace 3:
> <IRQ>
> __sched_core_tick+0x27/0x40
> scheduler_tick+0x1be/0x270
> ? tick_sched_handle.isra.18+0x60/0x60
> update_process_times+0x6a/0x90
> tick_sched_handle.isra.18+0x1f/0x60
> tick_sched_timer+0x47/0x80
> __hrtimer_run_queues+0x10a/0x280
> hrtimer_interrupt+0x10b/0x240
> __sysvec_apic_timer_interrupt+0x70/0x160
> sysvec_apic_timer_interrupt+0x9a/0xd0
> </IRQ>
> <TASK>
> asm_sysvec_apic_timer_interrupt+0x16/0x20
>
> Steps to reproduce:
> 1. Enable CONFIG_SCHED_DEBUG and CONFIG_SCHED_CORE when compiling
>     the kernel
> 2. echo 1 > /sys/kernel/debug/clear_warn_once
>     echo "WARN_DOUBLE_CLOCK" > /sys/kernel/debug/sched/features
> 3. Run the linux/tools/testing/selftests/sched/cs_prctl_test test
>
> Signed-off-by: Hao Jia <jiahao.os@xxxxxxxxxxxxx>
> ---
>   kernel/sched/core.c       |  5 ++++-
>   kernel/sched/core_sched.c |  4 +++-
>   kernel/sched/sched.h      | 10 +++++++++-
>   3 files changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index daff72f00385..fcf5e4faec34 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -5951,6 +5951,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
>   	rq->core->core_cookie = 0UL;
>   	if (rq->core->core_forceidle_count) {
>   		if (!core_clock_updated) {
> +			rq_clock_clear_update(rq->core);
>   			update_rq_clock(rq->core);
>   			core_clock_updated = true;
>   		}
> @@ -6007,8 +6008,10 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
>   		 * pick_next_task(). If the current cpu is not the core,
>   		 * the core may also have been updated above.
>   		 */
> -		if (i != cpu && (rq_i != rq->core || !core_clock_updated))
> +		if (i != cpu && (rq_i != rq->core || !core_clock_updated)) {
> +			rq_clock_clear_update(rq_i);
>   			update_rq_clock(rq_i);
> +		}
>   
>   		p = rq_i->core_pick = pick_task(rq_i);
>   		if (!max || prio_less(max, p, fi_before))
> diff --git a/kernel/sched/core_sched.c b/kernel/sched/core_sched.c
> index a57fd8f27498..70a6f36fd830 100644
> --- a/kernel/sched/core_sched.c
> +++ b/kernel/sched/core_sched.c
> @@ -291,8 +291,10 @@ void __sched_core_tick(struct rq *rq)
>   	if (!rq->core->core_forceidle_count)
>   		return;
>   
> -	if (rq != rq->core)
> +	if (rq != rq->core) {
> +		rq_clock_clear_update(rq->core);
>   		update_rq_clock(rq->core);
> +	}
>   
>   	__sched_core_account_forceidle(rq);
>   }
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index a4a20046e586..1a2c40c413c2 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -2544,8 +2544,16 @@ static inline void double_rq_clock_clear_update(struct rq *rq1, struct rq *rq2)
>   	rq2->clock_update_flags &= (RQCF_REQ_SKIP|RQCF_ACT_SKIP);
>   #endif
>   }
> -#else
> +
> +#ifdef CONFIG_SCHED_CORE
> +static inline void rq_clock_clear_update(struct rq *rq)
> +{
> +	rq->clock_update_flags &= (RQCF_REQ_SKIP|RQCF_ACT_SKIP);
> +}
> +#endif
> +#else /* CONFIG_SCHED_DEBUG */
>   static inline void double_rq_clock_clear_update(struct rq *rq1, struct rq *rq2) {}
> +static inline void rq_clock_clear_update(struct rq *rq) {}
>   #endif
>   
>   #ifdef CONFIG_SMP