linux-kernel - Re: [PATCH 1/1] sched/topology: Make sched_init_numa() use a set for the deduplicating sort

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Message-ID: <jhj1re00zpp.mognet@arm.com>
Date:   Mon, 01 Feb 2021 11:55:30 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>,
        linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, peterz@...radead.org, vincent.guittot@...aro.org,
        morten.rasmussen@....com, mgorman@...e.de,
        song.bao.hua@...ilicon.com
Subject: Re: [PATCH 1/1] sched/topology: Make sched_init_numa() use a set for the deduplicating sort

On 01/02/21 10:53, Dietmar Eggemann wrote:
> On 22/01/2021 13:39, Valentin Schneider wrote:
>
> [...]
>
>> @@ -1705,7 +1702,7 @@ void sched_init_numa(void)
>>      /* Compute default topology size */
>>      for (i = 0; sched_domain_topology[i].mask; i++);
>>
>> -	tl = kzalloc((i + level + 1) *
>> +	tl = kzalloc((i + nr_levels) *
>>                      sizeof(struct sched_domain_topology_level), GFP_KERNEL);
>>      if (!tl)
>>              return;
>
> This hunk creates issues during startup on my Arm64 juno board on tip/sched/core.
>
> ---8<---
>
> From: Dietmar Eggemann <dietmar.eggemann@....com>
> Date: Mon, 1 Feb 2021 09:58:04 +0100
> Subject: [PATCH] sched/topology: Fix sched_domain_topology_level alloc in
>  sched_init_numa
>
> 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.
>
> This led to an Oops (on Arm64 juno with CONFIG_SCHED_DEBUG):
>
> sched_init_domains
>   build_sched_domains()
>     __free_domain_allocs()
>       __sdt_free() {
>       ...
>         for_each_sd_topology(tl)
>         ...
>           sd = *per_cpu_ptr(sdd->sd, j); <--
>         ...
>       }
>
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@....com>

Damn, I forgot the topology level stuff must terminate in a NULL'd
sentinel! Vincent fixed the same thing a few years ago...

  c515db8cd311 ("sched/numa: Fix initialization of sched_domain_topology for NUMA")

Thanks for fixing up my mistake, I ought to have tested !NUMA setups.