linux-kernel - Re: [PATCH v2] sched/topology: fix kernel crash when a CPU is hotplugged in a memoryless node

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Message-ID: <20190220170841.GM32494@hirez.programming.kicks-ass.net>
Date:   Wed, 20 Feb 2019 18:08:41 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Laurent Vivier <lvivier@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Borislav Petkov <bp@...e.de>,
        David Gibson <david@...son.dropbear.id.au>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nathan Fontenot <nfont@...ux.vnet.ibm.com>,
        Michael Bringmann <mwb@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v2] sched/topology: fix kernel crash when a CPU is
 hotplugged in a memoryless node

On Wed, Feb 20, 2019 at 05:55:20PM +0100, Laurent Vivier wrote:
> index 3f35ba1d8fde..372278605f0d 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -1651,6 +1651,7 @@ void sched_init_numa(void)
>  	 */
>  	tl[i++] = (struct sched_domain_topology_level){
>  		.mask = sd_numa_mask,
> +		.flags = SDTL_OVERLAP,

This makes no sense what so ever. The numa identify node should not have
overlap with other domains.

Are you sure this is not because of the utterly broken powerpc nonsense
where they move CPUs between nodes?

>  		.numa_level = 0,
>  		SD_INIT_NAME(NODE)
>  	};
> -- 
> 2.20.1
>