linux-kernel - Re: [PATCH v1] sched/uclamp: Skip uclamp_rq_dec() for non-final dequeue of delayed tasks

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAB8ipk-6=jZt5LZ9q9ehCE2PhhrBz4xV7BSLiqUda7=arm2rDQ@mail.gmail.com>
Date: Tue, 1 Jul 2025 18:49:05 +0800
From: Xuewen Yan <xuewen.yan94@...il.com>
To: Zihuan Zhang <zhangzihuan@...inos.cn>
Cc: xuewen.yan@...soc.com, vincent.guittot@...aro.org, mingo@...hat.com, 
	peterz@...radead.org, juri.lelli@...hat.com, rostedt@...dmis.org, 
	bsegall@...gle.com, mgorman@...e.de, vschneid@...hat.com, 
	hongyan.xia2@....com, linux-kernel@...r.kernel.org, ke.wang@...soc.com, 
	di.shen@...soc.com, kprateek.nayak@....com, kuyo.chang@...iatek.com, 
	juju.sung@...iatek.com, qyousef@...alina.io
Subject: Re: [PATCH v1] sched/uclamp: Skip uclamp_rq_dec() for non-final
 dequeue of delayed tasks

Hi zihuan,

On Tue, Jul 1, 2025 at 5:34 PM Zihuan Zhang <zhangzihuan@...inos.cn> wrote:
>
> Currently, uclamp_rq_inc() skips updating the clamp aggregation for
> delayed tasks unless ENQUEUE_DELAYED is set, to ensure we only track the
> real enqueue of a task that was previously marked as sched_delayed.
>
> However, the corresponding uclamp_rq_dec() path only checks
> sched_delayed, and misses the DEQUEUE_DELAYED flag. As a result, we may
> skip dec for a delayed task that is now being truly dequeued, leading to
> uclamp aggregation mismatch.
>
> This patch makes uclamp_rq_dec() consistent with uclamp_rq_inc() by
> checking both sched_delayed and DEQUEUE_DELAYED, ensuring correct
> accounting symmetry.
>
> Fixes: 90ca9410dab2 ("sched/uclamp: Align uclamp and util_est and call before freq update")
> Signed-off-by: Zihuan Zhang <zhangzihuan@...inos.cn>
> ---
>  kernel/sched/core.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 8988d38d46a3..99f1542cff7d 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1781,7 +1781,7 @@ static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p, int flags
>                 rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
>  }
>
> -static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
> +static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p, int flags)
>  {
>         enum uclamp_id clamp_id;
>
> @@ -1797,7 +1797,8 @@ static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
>         if (unlikely(!p->sched_class->uclamp_enabled))
>                 return;
>
> -       if (p->se.sched_delayed)
> +       /* Skip dec if this is a delayed task not being truly dequeued */
> +       if (p->se.sched_delayed && !(flags & DEQUEUE_DELAYED))
>                 return;

Consider the __sched_setscheduler()，when changing the delayed-task's
sched-class，your patch would dec the uclamp twice.

BR
---
xuewen

>
>         for_each_clamp_id(clamp_id)
> @@ -2039,7 +2040,7 @@ static void __init init_uclamp(void)
>
>  #else /* !CONFIG_UCLAMP_TASK */
>  static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p, int flags) { }
> -static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p) { }
> +static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p, int flags) { }
>  static inline void uclamp_fork(struct task_struct *p) { }
>  static inline void uclamp_post_fork(struct task_struct *p) { }
>  static inline void init_uclamp(void) { }
> @@ -2112,7 +2113,7 @@ inline bool dequeue_task(struct rq *rq, struct task_struct *p, int flags)
>          * Must be before ->dequeue_task() because ->dequeue_task() can 'fail'
>          * and mark the task ->sched_delayed.
>          */
> -       uclamp_rq_dec(rq, p);
> +       uclamp_rq_dec(rq, p, flags);
>         return p->sched_class->dequeue_task(rq, p, flags);
>  }
>
> --
> 2.25.1
>