linux-kernel - Re: [PATCH] ia64: Ensure proper NUMA distance and possible map initialization

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Date:   Wed, 24 Mar 2021 19:59:39 +0100
From:   John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Valentin Schneider <valentin.schneider@....com>
Cc:     linux-kernel@...r.kernel.org,
        "linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
        debian-ia64 <debian-ia64@...ts.debian.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Sergei Trofimovich <slyfox@...too.org>,
        Anatoly Pugachev <matorola@...il.com>
Subject: Re: [PATCH] ia64: Ensure proper NUMA distance and possible map
 initialization

Hi!

On 3/24/21 7:54 PM, Andrew Morton wrote:
> On Thu, 18 Mar 2021 13:06:17 +0000 Valentin Schneider <valentin.schneider@....com> wrote:
> 
>> John Paul reported a warning about bogus NUMA distance values spurred by
>> commit:
>>
>>   620a6dc40754 ("sched/topology: Make sched_init_numa() use a set for the deduplicating sort")
>>
>> In this case, the afflicted machine comes up with a reported 256 possible
>> nodes, all of which are 0 distance away from one another. This was
>> previously silently ignored, but is now caught by the aforementioned
>> commit.
>>
>> The culprit is ia64's node_possible_map which remains unchanged from its
>> initialization value of NODE_MASK_ALL. In John's case, the machine doesn't
>> have any SRAT nor SLIT table, but AIUI the possible map remains untouched
>> regardless of what ACPI tables end up being parsed. Thus, !online &&
>> possible nodes remain with a bogus distance of 0 (distances \in [0, 9] are
>> "reserved and have no meaning" as per the ACPI spec).
>>
>> Follow x86 / drivers/base/arch_numa's example and set the possible map to
>> the parsed map, which in this case seems to be the online map.
>>
>> Link: http://lore.kernel.org/r/255d6b5d-194e-eb0e-ecdd-97477a534441@physik.fu-berlin.de
>> Fixes: 620a6dc40754 ("sched/topology: Make sched_init_numa() use a set for the deduplicating sort")
>> Reported-by: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
>> Signed-off-by: Valentin Schneider <valentin.schneider@....com>
>> ---
>> This might need an earlier Fixes: tag, but all of this is quite old and
>> dusty (the git blame rabbit hole leads me to ~2008/2007)
>>
> 
> Thanks.  Is this worth a cc:stable tag?

Looks like the regression was introduced 5.12-rc1, so no need for backporting.

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer - glaubitz@...ian.org
`. `'   Freie Universitaet Berlin - glaubitz@...sik.fu-berlin.de
  `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913