linux-kernel - Re: [PATCH] sched/topology: remove unneeded do while loop in cpu_attach

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Message-ID: <20230620141120.GA2016469@hirez.programming.kicks-ass.net>
Date:   Tue, 20 Jun 2023 16:11:20 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/topology: remove unneeded do while loop in
 cpu_attach_domain()

On Sat, Jun 17, 2023 at 04:19:26PM +0800, Miaohe Lin wrote:
> When sg != sd->groups, the do while loop would cause deadloop here. But
> that won't occur because sg is always equal to sd->groups now. Remove
> this unneeded do while loop.

This Changelog makes no sense to me.. Yes, as is the do {} while loop is
dead code, but it *should* have read like:

	do {
		sg->flags = 0;
		sg = sg->next;
	} while (sg != sd->groups);

as I noted here:

  https://lore.kernel.org/all/20230523105935.GN83892@hirez.programming.kicks-ass.net/T/#u

So what this changelog should argue is how there cannot be multiple
groups here -- or if there can be, add the missing iteration.

> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  kernel/sched/topology.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index ca4472281c28..9010c93c3fdb 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -750,10 +750,7 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
>  			 * domain for convenience. Clear such flags since
>  			 * the child is being destroyed.
>  			 */
> -			do {
> -				sg->flags = 0;
> -			} while (sg != sd->groups);
> -
> +			sg->flags = 0;
>  			sd->child = NULL;
>  		}
>  	}
> -- 
> 2.27.0
>