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

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Message-Id: <20210318130617.896309-1-valentin.schneider@arm.com>
Date:   Thu, 18 Mar 2021 13:06:17 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     linux-kernel@...r.kernel.org,
        "linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
        debian-ia64 <debian-ia64@...ts.debian.org>
Cc:     John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        "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: [PATCH] ia64: Ensure proper NUMA distance and possible map initialization

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)

Alternatively, can we deprecate ia64 already?
---
 arch/ia64/kernel/acpi.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/ia64/kernel/acpi.c b/arch/ia64/kernel/acpi.c
index a5636524af76..e2af6b172200 100644
--- a/arch/ia64/kernel/acpi.c
+++ b/arch/ia64/kernel/acpi.c
@@ -446,7 +446,8 @@ void __init acpi_numa_fixup(void)
 	if (srat_num_cpus == 0) {
 		node_set_online(0);
 		node_cpuid[0].phys_id = hard_smp_processor_id();
-		return;
+		slit_distance(0, 0) = LOCAL_DISTANCE;
+		goto out;
 	}
 
 	/*
@@ -489,7 +490,7 @@ void __init acpi_numa_fixup(void)
 			for (j = 0; j < MAX_NUMNODES; j++)
 				slit_distance(i, j) = i == j ?
 					LOCAL_DISTANCE : REMOTE_DISTANCE;
-		return;
+		goto out;
 	}
 
 	memset(numa_slit, -1, sizeof(numa_slit));
@@ -514,6 +515,8 @@ void __init acpi_numa_fixup(void)
 		printk("\n");
 	}
 #endif
+out:
+	node_possible_map = node_online_map;
 }
 #endif				/* CONFIG_ACPI_NUMA */
 
-- 
2.25.1