Re: [PATCH v2] sched/core: Fix reset-on-fork from RT with uclamp
From: Dietmar Eggemann
Date: Thu Apr 16 2020 - 07:07:37 EST
On 16.04.20 10:59, Quentin Perret wrote:
> uclamp_fork() resets the uclamp values to their default when the
> reset-on-fork flag is set. It also checks whether the task has a RT
> policy, and sets its uclamp.min to 1024 accordingly. However, during
> reset-on-fork, the task's policy is lowered to SCHED_NORMAL right after,
> hence leading to an erroneous uclamp.min setting for the new task if it
> was forked from RT.
>
> Fix this by removing the unnecessary check on rt_task() in
> uclamp_fork() as this doesn't make sense if the reset-on-fork flag is
> set.
>
> Fixes: 1a00d999971c ("sched/uclamp: Set default clamps for RT tasks")
> Reported-by: Chitti Babu Theegala <ctheegal@xxxxxxxxxxxxxx>
> Reviewed-by: Patrick Bellasi <patrick.bellasi@xxxxxxxxxx>
> Signed-off-by: Quentin Perret <qperret@xxxxxxxxxx>
> ---
> Changes in v2:
> - Added missing 'Fixes:' tag (Patrick)
> - Removed unnecessary local variable (Doug, Patrick)
> ---
> kernel/sched/core.c | 9 ++-------
> 1 file changed, 2 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 3a61a3b8eaa9..9a2fbf98fd6f 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1232,13 +1232,8 @@ static void uclamp_fork(struct task_struct *p)
> return;
>
> for_each_clamp_id(clamp_id) {
> - unsigned int clamp_value = uclamp_none(clamp_id);
> -
> - /* By default, RT tasks always get 100% boost */
> - if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
> - clamp_value = uclamp_none(UCLAMP_MAX);
> -
> - uclamp_se_set(&p->uclamp_req[clamp_id], clamp_value, false);
> + uclamp_se_set(&p->uclamp_req[clamp_id],
> + uclamp_none(clamp_id), false);
> }
> }
LGTM.
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>