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sched/fair: Fix enqueue_task_fair warning

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When a cfs rq is throttled, the latter and its child are removed from the
leaf list but their nr_running is not changed which includes staying higher
than 1. When a task is enqueued in this throttled branch, the cfs rqs must
be added back in order to ensure correct ordering in the list but this can
only happens if nr_running == 1.
When cfs bandwidth is used, we call unconditionnaly list_add_leaf_cfs_rq()
when enqueuing an entity to make sure that the complete branch will be
added.

Similarly unthrottle_cfs_rq() can stop adding cfs in the list when a parent
is throttled. Iterate the remaining entity to ensure that the complete
branch will be added in the list.

Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: stable@vger.kernel.org
Cc: stable@vger.kernel.org #v5.1+
Link: https://lkml.kernel.org/r/20200306135257.25044-1-vincent.guittot@linaro.org
This commit is contained in:
Vincent Guittot 2020-03-06 14:52:57 +01:00 committed by Peter Zijlstra
parent 14533a16c4
commit fe61468b2c
1 changed files with 22 additions and 4 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

26
kernel/sched/fair.c
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@ -4136,6 +4136,7 @@ static inline void check_schedstat_required(void)
#endif
}
static inline bool cfs_bandwidth_used(void);
/*
* MIGRATION
@ -4214,10 +4215,16 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
__enqueue_entity(cfs_rq, se);
se->on_rq = 1;
if (cfs_rq->nr_running == 1) {
/*
* When bandwidth control is enabled, cfs might have been removed
* because of a parent been throttled but cfs->nr_running > 1. Try to
* add it unconditionnally.
*/
if (cfs_rq->nr_running == 1 || cfs_bandwidth_used())
list_add_leaf_cfs_rq(cfs_rq);
if (cfs_rq->nr_running == 1)
check_enqueue_throttle(cfs_rq);
}
}
static void __clear_buddies_last(struct sched_entity *se)
@ -4808,11 +4815,22 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
break;
}
assert_list_leaf_cfs_rq(rq);
if (!se)
add_nr_running(rq, task_delta);
/*
* The cfs_rq_throttled() breaks in the above iteration can result in
* incomplete leaf list maintenance, resulting in triggering the
* assertion below.
*/
for_each_sched_entity(se) {
cfs_rq = cfs_rq_of(se);
list_add_leaf_cfs_rq(cfs_rq);
}
assert_list_leaf_cfs_rq(rq);
/* Determine whether we need to wake up potentially idle CPU: */
if (rq->curr == rq->idle && rq->cfs.nr_running)
resched_curr(rq);