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From: Valentin Schneider <vschneid@redhat.com>
To: Daniil Dulov <d.dulov@aladdin.ru>, Ingo Molnar <mingo@redhat.com>
Cc: Daniil Dulov <d.dulov@aladdin.ru>, Peter Zijlstra
 <peterz@infradead.org>, Juri Lelli <juri.lelli@redhat.com>, Vincent
 Guittot <vincent.guittot@linaro.org>, Dietmar Eggemann
 <dietmar.eggemann@arm.com>, Steven Rostedt <rostedt@goodmis.org>, Ben
 Segall <bsegall@google.com>, Mel
 Gorman <mgorman@suse.de>, Daniel Bristot de Oliveira <bristot@redhat.com>,
 linux-kernel@vger.kernel.org, lvc-project@linuxtesting.org
Subject: Re: [PATCH] sched/topology: Check return value of zalloc_cpumask_var()
In-Reply-To: <20240307132340.13192-1-d.dulov@aladdin.ru>
References: <20240307132340.13192-1-d.dulov@aladdin.ru>
Date: Thu, 14 Mar 2024 17:25:14 +0100
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On 07/03/24 16:23, Daniil Dulov wrote:
> zalloc_cpumask_var() returns false if mask was not allocated.
> So, let's check if cpu masks are allocated successfully.
>
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> Fixes: 8d5dc5126bb2 ("sched/topology: Small cleanup")
> Signed-off-by: Daniil Dulov <d.dulov@aladdin.ru>
> ---
>  kernel/sched/topology.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 10d1391e7416..2df98ffdfe16 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -2600,9 +2600,10 @@ int __init sched_init_domains(const struct cpumask *cpu_map)
>  {
>       int err;
>
> -	zalloc_cpumask_var(&sched_domains_tmpmask, GFP_KERNEL);
> -	zalloc_cpumask_var(&sched_domains_tmpmask2, GFP_KERNEL);
> -	zalloc_cpumask_var(&fallback_doms, GFP_KERNEL);
> +	if (!zalloc_cpumask_var(&sched_domains_tmpmask, GFP_KERNEL) ||
> +	    !zalloc_cpumask_var(&sched_domains_tmpmask2, GFP_KERNEL) ||
> +	    !zalloc_cpumask_var(&fallback_doms, GFP_KERNEL))
> +		return -ENOMEM;

Despite returning an int, sched_init_domains()' return value is ignored by
sched_init_smp()

The int return was added in 2006 by:
  51888ca25a03 ("[PATCH] sched_domain: handle kmalloc failure")
but it looks like sched_init_smp() never checked it.

Now, allocation failures this early in init really isn't good and more
things are bound to explode, but I suppose you could add a return value
check in sched_init_smp() and WARN on anything non-zero. Without
sched_domain's, we'll still have the boot CPU doing useful work.

>
>       arch_update_cpu_topology();
>       asym_cpu_capacity_scan();
> --
> 2.25.1