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Date: Wed, 17 Aug 2022 17:01:32 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Chengming Zhou <zhouchengming@...edance.com>
Cc: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
vschneid@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 6/9] sched/fair: fix another detach on unattached task
corner case
On Mon, 8 Aug 2022 at 14:58, Chengming Zhou <zhouchengming@...edance.com> wrote:
>
> commit 7dc603c9028e ("sched/fair: Fix PELT integrity for new tasks")
> fixed two load tracking problems for new task, including detach on
> unattached new task problem.
>
> There still left another detach on unattached task problem for the task
> which has been woken up by try_to_wake_up() and waiting for actually
> being woken up by sched_ttwu_pending().
>
> try_to_wake_up(p)
> cpu = select_task_rq(p)
> if (task_cpu(p) != cpu)
> set_task_cpu(p, cpu)
> migrate_task_rq_fair()
> remove_entity_load_avg() --> unattached
> se->avg.last_update_time = 0;
> __set_task_cpu()
> ttwu_queue(p, cpu)
> ttwu_queue_wakelist()
> __ttwu_queue_wakelist()
>
> task_change_group_fair()
> detach_task_cfs_rq()
> detach_entity_cfs_rq()
> detach_entity_load_avg() --> detach on unattached task
> set_task_rq()
> attach_task_cfs_rq()
> attach_entity_cfs_rq()
> attach_entity_load_avg()
>
> The reason of this problem is similar, we should check in detach_entity_cfs_rq()
> that se->avg.last_update_time != 0, before do detach_entity_load_avg().
>
> This patch move detach/attach_entity_cfs_rq() functions up to be together
> with other load tracking functions to avoid to use another #ifdef CONFIG_SMP.
>
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
> ---
> kernel/sched/fair.c | 132 +++++++++++++++++++++++---------------------
> 1 file changed, 68 insertions(+), 64 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index f52e7dc7f22d..4bc76d95a99d 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -874,9 +874,6 @@ void init_entity_runnable_average(struct sched_entity *se)
> void post_init_entity_util_avg(struct task_struct *p)
> {
> }
> -static void update_tg_load_avg(struct cfs_rq *cfs_rq)
> -{
> -}
> #endif /* CONFIG_SMP */
>
> /*
> @@ -3176,6 +3173,7 @@ void reweight_task(struct task_struct *p, int prio)
> load->inv_weight = sched_prio_to_wmult[prio];
> }
>
> +static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq);
> static inline int throttled_hierarchy(struct cfs_rq *cfs_rq);
>
> #ifdef CONFIG_FAIR_GROUP_SCHED
> @@ -4086,6 +4084,71 @@ static void remove_entity_load_avg(struct sched_entity *se)
> raw_spin_unlock_irqrestore(&cfs_rq->removed.lock, flags);
> }
>
> +#ifdef CONFIG_FAIR_GROUP_SCHED
> +/*
> + * Propagate the changes of the sched_entity across the tg tree to make it
> + * visible to the root
> + */
> +static void propagate_entity_cfs_rq(struct sched_entity *se)
> +{
> + struct cfs_rq *cfs_rq = cfs_rq_of(se);
> +
> + if (cfs_rq_throttled(cfs_rq))
> + return;
> +
> + if (!throttled_hierarchy(cfs_rq))
> + list_add_leaf_cfs_rq(cfs_rq);
> +
> + /* Start to propagate at parent */
> + se = se->parent;
> +
> + for_each_sched_entity(se) {
> + cfs_rq = cfs_rq_of(se);
> +
> + update_load_avg(cfs_rq, se, UPDATE_TG);
> +
> + if (cfs_rq_throttled(cfs_rq))
> + break;
> +
> + if (!throttled_hierarchy(cfs_rq))
> + list_add_leaf_cfs_rq(cfs_rq);
> + }
> +}
> +#else
> +static void propagate_entity_cfs_rq(struct sched_entity *se) { }
> +#endif
> +
> +static void detach_entity_cfs_rq(struct sched_entity *se)
> +{
> + struct cfs_rq *cfs_rq = cfs_rq_of(se);
> +
> + /*
> + * In case the task sched_avg hasn't been attached:
> + * - A forked task which hasn't been woken up by wake_up_new_task().
> + * - A task which has been woken up by try_to_wake_up() but is
> + * waiting for actually being woken up by sched_ttwu_pending().
> + */
> + if (!se->avg.last_update_time)
> + return;
The 2 lines above and the associated comment are the only relevant
part of the patch, aren't they ?
Is everything else just code moving from one place to another one
without change ?
> +
> + /* Catch up with the cfs_rq and remove our load when we leave */
> + update_load_avg(cfs_rq, se, 0);
> + detach_entity_load_avg(cfs_rq, se);
> + update_tg_load_avg(cfs_rq);
> + propagate_entity_cfs_rq(se);
> +}
> +
> +static void attach_entity_cfs_rq(struct sched_entity *se)
> +{
> + struct cfs_rq *cfs_rq = cfs_rq_of(se);
> +
> + /* Synchronize entity with its cfs_rq */
> + update_load_avg(cfs_rq, se, sched_feat(ATTACH_AGE_LOAD) ? 0 : SKIP_AGE_LOAD);
> + attach_entity_load_avg(cfs_rq, se);
> + update_tg_load_avg(cfs_rq);
> + propagate_entity_cfs_rq(se);
> +}
> +
> static inline unsigned long cfs_rq_runnable_avg(struct cfs_rq *cfs_rq)
> {
> return cfs_rq->avg.runnable_avg;
> @@ -4308,11 +4371,8 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
> }
>
> static inline void remove_entity_load_avg(struct sched_entity *se) {}
> -
> -static inline void
> -attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
> -static inline void
> -detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
> +static inline void detach_entity_cfs_rq(struct sched_entity *se) {}
> +static inline void attach_entity_cfs_rq(struct sched_entity *se) {}
>
> static inline int newidle_balance(struct rq *rq, struct rq_flags *rf)
> {
> @@ -11519,62 +11579,6 @@ static inline bool vruntime_normalized(struct task_struct *p)
> return false;
> }
>
> -#ifdef CONFIG_FAIR_GROUP_SCHED
> -/*
> - * Propagate the changes of the sched_entity across the tg tree to make it
> - * visible to the root
> - */
> -static void propagate_entity_cfs_rq(struct sched_entity *se)
> -{
> - struct cfs_rq *cfs_rq = cfs_rq_of(se);
> -
> - if (cfs_rq_throttled(cfs_rq))
> - return;
> -
> - if (!throttled_hierarchy(cfs_rq))
> - list_add_leaf_cfs_rq(cfs_rq);
> -
> - /* Start to propagate at parent */
> - se = se->parent;
> -
> - for_each_sched_entity(se) {
> - cfs_rq = cfs_rq_of(se);
> -
> - update_load_avg(cfs_rq, se, UPDATE_TG);
> -
> - if (cfs_rq_throttled(cfs_rq))
> - break;
> -
> - if (!throttled_hierarchy(cfs_rq))
> - list_add_leaf_cfs_rq(cfs_rq);
> - }
> -}
> -#else
> -static void propagate_entity_cfs_rq(struct sched_entity *se) { }
> -#endif
> -
> -static void detach_entity_cfs_rq(struct sched_entity *se)
> -{
> - struct cfs_rq *cfs_rq = cfs_rq_of(se);
> -
> - /* Catch up with the cfs_rq and remove our load when we leave */
> - update_load_avg(cfs_rq, se, 0);
> - detach_entity_load_avg(cfs_rq, se);
> - update_tg_load_avg(cfs_rq);
> - propagate_entity_cfs_rq(se);
> -}
> -
> -static void attach_entity_cfs_rq(struct sched_entity *se)
> -{
> - struct cfs_rq *cfs_rq = cfs_rq_of(se);
> -
> - /* Synchronize entity with its cfs_rq */
> - update_load_avg(cfs_rq, se, sched_feat(ATTACH_AGE_LOAD) ? 0 : SKIP_AGE_LOAD);
> - attach_entity_load_avg(cfs_rq, se);
> - update_tg_load_avg(cfs_rq);
> - propagate_entity_cfs_rq(se);
> -}
> -
> static void detach_task_cfs_rq(struct task_struct *p)
> {
> struct sched_entity *se = &p->se;
> --
> 2.36.1
>
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