linux-kernel - Re: [PATCH 5.10+5.4 2/3] sched/topology: Fix sched_domain_topology_level alloc in sched_init

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Message-ID: <39660e162b54f241cdb571e0029c26d4596ec8e0.camel@perches.com>
Date:   Sat, 05 Mar 2022 09:13:21 -0800
From:   Joe Perches <joe@...ches.com>
To:     dann frazier <dann.frazier@...onical.com>, stable@...r.kernel.org
Cc:     Miao Xie <miaox@...fujitsu.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Barry Song <song.bao.hua@...ilicon.com>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        Sergei Trofimovich <slyfox@...too.org>,
        Anatoly Pugachev <matorola@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5.10+5.4 2/3] sched/topology: Fix
 sched_domain_topology_level alloc in sched_init_numa()

On Sat, 2022-03-05 at 09:44 -0700, dann frazier wrote:
> From: Dietmar Eggemann <dietmar.eggemann@....com>
> 
> commit 71e5f6644fb2f3304fcb310145ded234a37e7cc1 upstream.
> 
> Commit "sched/topology: Make sched_init_numa() use a set for the
> deduplicating sort" allocates 'i + nr_levels (level)' instead of
> 'i + nr_levels + 1' sched_domain_topology_level.
[]
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
[]
> @@ -1655,7 +1655,7 @@ void sched_init_numa(void)
>  	/* Compute default topology size */
>  	for (i = 0; sched_domain_topology[i].mask; i++);

Thanks.

Couple trivial notes:

A trailing semicolon in a for loop, "for (...);" can be error prone
and is also the only usage of that style in kernel/ path.

A more common usage might be:

	i = 0;
	while (sched_domain_topology[i].mask)
		i++;

> -	tl = kzalloc((i + nr_levels) *
> +	tl = kzalloc((i + nr_levels + 1) *
>  			sizeof(struct sched_domain_topology_level), GFP_KERNEL);

kcalloc would be better, although the array is completely set
by the loop below so the zeroing isn't necessary.
Maybe use kmalloc_array.

Doubtful there's an overall impact though.