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SubjectRe: [PATCH] sched,fair: use list_for_each_entry() in print_cfs_stats()
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On 25/09/2020 21:10, Hui Su wrote:
> Macro for_each_leaf_cfs_rq_safe() use list_for_each_entry_safe(),
> which can against removal of list entry, but we only
> print the cfs_rq data and won't remove the list entry in
> print_cfs_stats().
>
> Thus, add macro for_each_leaf_cfs_rq() based on
> list_for_each_entry(), and use for_each_leaf_cfs_rq() in
> print_cfs_stats().
>
> Signed-off-by: Hui Su <sh_def@163.com>
> ---
> kernel/sched/fair.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1a68a0536add..d40dfb4349b0 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -391,11 +391,16 @@ static inline void assert_list_leaf_cfs_rq(struct rq *rq)
> SCHED_WARN_ON(rq->tmp_alone_branch != &rq->leaf_cfs_rq_list);
> }
>
> -/* Iterate thr' all leaf cfs_rq's on a runqueue */
> +/* Iterate thr' all leaf cfs_rq's on a runqueue safely */
> #define for_each_leaf_cfs_rq_safe(rq, cfs_rq, pos) \
> list_for_each_entry_safe(cfs_rq, pos, &rq->leaf_cfs_rq_list, \
> leaf_cfs_rq_list)
>
> +/* Iterate thr' all leaf cfs_rq's on a runqueue */
> +#define for_each_leaf_cfs_rq(rq, cfs_rq) \
> + list_for_each_entry(cfs_rq, &rq->leaf_cfs_rq_list, \
> + leaf_cfs_rq_list)
> +
> /* Do the two (enqueued) entities belong to the same group ? */
> static inline struct cfs_rq *
> is_same_group(struct sched_entity *se, struct sched_entity *pse)
> @@ -11185,10 +11190,10 @@ const struct sched_class fair_sched_class
> #ifdef CONFIG_SCHED_DEBUG
> void print_cfs_stats(struct seq_file *m, int cpu)
> {
> - struct cfs_rq *cfs_rq, *pos;
> + struct cfs_rq *cfs_rq;
>
> rcu_read_lock();
> - for_each_leaf_cfs_rq_safe(cpu_rq(cpu), cfs_rq, pos)
> + for_each_leaf_cfs_rq(cpu_rq(cpu), cfs_rq)
> print_cfs_rq(m, cpu, cfs_rq);
> rcu_read_unlock();
> }

IMHO, for_each_leaf_cfs_rq_safe() was introduced in commit a9e7f6544b9c
("sched/fair: Fix O(nr_cgroups) in load balance path") and reintroduced
again by commit 039ae8bcf7a5 ("sched/fair: Fix O(nr_cgroups) in the load
balancing path") to prevent races between tasks running
print_cfs_stats() and today's __update_blocked_fair() ->
list_del_leaf_cfs_rq(cfs_rq).

Your patch doesn't compile w/ !CONFIG_FAIR_GROUP_SCHED.

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