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    Subject[RFC tg_shares_up improvements - v1 04/12] sched: fix load corruption from update_cfs_shares
    as part of enqueue_entity both a new entity weight and its contribution to the
    queuing cfs_rq / rq are updated. Since update_cfs_shares will only update the
    queueing weights when the entity is on_rq (which in this case it is not yet),
    there's a dependency loop here:

    update_cfs_shares needs account_entity_enqueue to update cfs_rq->load.weight
    account_entity_enqueue needs the updated weight for the queuing cfs_rq load[*]

    Fix this and avoid spurious dequeue/enqueues by issuing update_cfs_shares as
    if we had accounted the enqueue already.

    This was also resulting in rq->load corruption previously.

    [*]: this dependency also exists when using the group cfs_rq w/
    update_cfs_shares as the weight of the enqueued entity changes without the
    load being updated.

    Signed-off-by: Paul Turner <pjt@google.com>
    ---
    kernel/sched_fair.c | 16 ++++++++--------
    1 file changed, 8 insertions(+), 8 deletions(-)

    Index: kernel/sched_fair.c
    ===================================================================
    --- kernel/sched_fair.c.orig
    +++ kernel/sched_fair.c
    @@ -718,7 +718,7 @@ static void reweight_entity(struct cfs_r
    account_entity_enqueue(cfs_rq, se);
    }

    -static void update_cfs_shares(struct cfs_rq *cfs_rq)
    +static void update_cfs_shares(struct cfs_rq *cfs_rq, long weight_delta)
    {
    struct task_group *tg;
    struct sched_entity *se;
    @@ -732,7 +732,7 @@ static void update_cfs_shares(struct cfs
    if (!se)
    return;

    - load = cfs_rq->load.weight;
    + load = cfs_rq->load.weight + weight_delta;

    load_weight = atomic_read(&tg->load_weight);
    load_weight -= cfs_rq->load_contribution;
    @@ -754,7 +754,7 @@ static inline void update_cfs_load(struc
    {
    }

    -static inline void update_cfs_shares(struct cfs_rq *cfs_rq)
    +static inline void update_cfs_shares(struct cfs_rq *cfs_rq, long weight_delta)
    {
    }
    #endif /* CONFIG_FAIR_GROUP_SCHED */
    @@ -881,8 +881,8 @@ enqueue_entity(struct cfs_rq *cfs_rq, st
    */
    update_curr(cfs_rq);
    update_cfs_load(cfs_rq, 0);
    + update_cfs_shares(cfs_rq_of(se), se->load.weight);
    account_entity_enqueue(cfs_rq, se);
    - update_cfs_shares(cfs_rq_of(se));

    if (flags & ENQUEUE_WAKEUP) {
    place_entity(cfs_rq, se, 0);
    @@ -944,7 +944,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, st
    update_cfs_load(cfs_rq, 0);
    account_entity_dequeue(cfs_rq, se);
    update_min_vruntime(cfs_rq);
    - update_cfs_shares(cfs_rq_of(se));
    + update_cfs_shares(cfs_rq_of(se), 0);

    /*
    * Normalize the entity after updating the min_vruntime because the
    @@ -1177,7 +1177,7 @@ enqueue_task_fair(struct rq *rq, struct
    struct cfs_rq *cfs_rq = cfs_rq_of(se);

    update_cfs_load(cfs_rq, 0);
    - update_cfs_shares(cfs_rq);
    + update_cfs_shares(cfs_rq, 0);
    }

    hrtick_update(rq);
    @@ -1207,7 +1207,7 @@ static void dequeue_task_fair(struct rq
    struct cfs_rq *cfs_rq = cfs_rq_of(se);

    update_cfs_load(cfs_rq, 0);
    - update_cfs_shares(cfs_rq);
    + update_cfs_shares(cfs_rq, 0);
    }

    hrtick_update(rq);
    @@ -2030,7 +2030,7 @@ static int tg_shares_up(struct task_grou
    * We need to update shares after updating tg->load_weight in
    * order to adjust the weight of groups with long running tasks.
    */
    - update_cfs_shares(cfs_rq);
    + update_cfs_shares(cfs_rq, 0);

    raw_spin_unlock_irqrestore(&rq->lock, flags);

    --



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