Reviewed-by: Cheng Jian <cj.chengjian@huawei.com> 在 2021/10/23 17:09, wjy 写道:

From: Vincent Guittot <vincent.guittot@linaro.org>

stable inclusion from stable-v5.10.44 commit 32e22db8b25ea165bd9e446c7f92b089c8568eaf bugzilla: https://bugzilla.openeuler.org/show_bug.cgi?id=379 CVE: NA

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commit 02da26ad5ed6ea8680e5d01f20661439611ed776 upstream.

During the update of fair blocked load (__update_blocked_fair()), we update the contribution of the cfs in tg->load_avg if cfs_rq's pelt has decayed. Nevertheless, the pelt values of a cfs_rq could have been recently updated while propagating the change of a child. In this case, cfs_rq's pelt will not decayed because it has already been updated and we don't update tg->load_avg.

__update_blocked_fair ... for_each_leaf_cfs_rq_safe: child cfs_rq update cfs_rq_load_avg() for child cfs_rq ... update_load_avg(cfs_rq_of(se), se, 0) ... update cfs_rq_load_avg() for parent cfs_rq -propagation of child's load makes parent cfs_rq->load_sum becoming null -UPDATE_TG is not set so it doesn't update parent cfs_rq->tg_load_avg_contrib .. for_each_leaf_cfs_rq_safe: parent cfs_rq update cfs_rq_load_avg() for parent cfs_rq - nothing to do because parent cfs_rq has already been updated recently so cfs_rq->tg_load_avg_contrib is not updated ... parent cfs_rq is decayed list_del_leaf_cfs_rq parent cfs_rq - but it still contibutes to tg->load_avg

we must set UPDATE_TG flags when propagting pending load to the parent

Fixes: 039ae8bcf7a5 ("sched/fair: Fix O(nr_cgroups) in the load balancing path") Reported-by: Odin Ugedal <odin@uged.al> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Odin Ugedal <odin@uged.al> Link: https://lkml.kernel.org/r/20210527122916.27683-3-vincent.guittot@linaro.org Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: wjy <464310675@qq.com> --- kernel/sched/fair.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 1ad0e52487f6..43497d88a330 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7961,7 +7961,7 @@ static bool __update_blocked_fair(struct rq *rq, bool *done) /* Propagate pending load changes to the parent, if any: */ se = cfs_rq->tg->se[cpu]; if (se && !skip_blocked_update(se)) - update_load_avg(cfs_rq_of(se), se, 0); + update_load_avg(cfs_rq_of(se), se, UPDATE_TG);

/* * There can be a lot of idle CPU cgroups. Don't let fully