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Date: Fri, 2 Nov 2018 11:50:03 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: John Garry <john.garry@...wei.com>
Cc: "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
Anshuman Khandual <anshuman.khandual@....com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
linux-kernel@...r.kernel.org, Linuxarm <linuxarm@...wei.com>,
Rob Herring <robh+dt@...nel.org>,
Frank Rowand <frowand.list@...il.com>,
Ingo Molnar <mingo@...hat.com>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>
Subject: Re: Crash report: Broken NUMA distance map causes crash on arm64
system
On Thu, Nov 01, 2018 at 10:01:05AM +0000, John Garry wrote:
> On 31/10/2018 20:46, Peter Zijlstra wrote:
> > > I also note that if I apply the patch, below, to reject the invalid NUMA
> > > distance, we're still getting a warning/error:
> > >
> > > [ 7.144407] CPU: All CPU(s) started at EL2
> > > [ 7.148678] alternatives: patching kernel code
> > > [ 7.153557] ERROR: Node-0 not representative
> > > [ 7.153557]
> > > [ 7.159365] 10 15 20 25
> > > [ 7.162097] 15 10 25 30
> > > [ 7.164832] 20 25 10 15
> > > [ 7.167562] 25 30 15 10
> >
> > Yeah, that's an 'obviously' broken topology too.
> >
>
> AFAICT, this conforms to ACPI spec SLIT rules, and the kernel SLIT
> validation allows this also. So maybe we should shout louder here or even
> mark the SLIT as invalid if totally broken.
Right. Part of the problem is that I only have a few necessary
conditions (symmetry, trace-identity, node0-complete-distance) for the
distance table, but together they are not sufficient to determine if a
topology is 'good'.
(also, strictly speaking, non-symmetric topologies are possible -- think
uni-directional mesh links -- we've just not ever seen and validated
those)
That said; I can certainly make this code give up and warn harder on
those conditions.
How is something like the below?
---
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 9d74371e4aad..41e703dd875f 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1207,6 +1218,11 @@ sd_init(struct sched_domain_topology_level *tl,
return sd;
}
+static const struct cpumask *cpu_system_mask(int cpu)
+{
+ return cpu_online_mask;
+}
+
/*
* Topology list, bottom-up.
*/
@@ -1337,7 +1353,7 @@ void sched_init_numa(void)
int level = 0;
int i, j, k;
- sched_domains_numa_distance = kzalloc(sizeof(int) * nr_node_ids, GFP_KERNEL);
+ sched_domains_numa_distance = kzalloc(sizeof(int) * (nr_node_ids + 1), GFP_KERNEL);
if (!sched_domains_numa_distance)
return;
@@ -1353,39 +1369,22 @@ void sched_init_numa(void)
* node_distance(i,j) in order to avoid cubic time.
*/
next_distance = curr_distance;
+
for (i = 0; i < nr_node_ids; i++) {
for (j = 0; j < nr_node_ids; j++) {
- for (k = 0; k < nr_node_ids; k++) {
- int distance = node_distance(i, k);
-
- if (distance > curr_distance &&
- (distance < next_distance ||
- next_distance == curr_distance))
- next_distance = distance;
-
- /*
- * While not a strong assumption it would be nice to know
- * about cases where if node A is connected to B, B is not
- * equally connected to A.
- */
- if (sched_debug() && node_distance(k, i) != distance)
- sched_numa_warn("Node-distance not symmetric");
-
- if (sched_debug() && i && !find_numa_distance(distance))
- sched_numa_warn("Node-0 not representative");
- }
- if (next_distance != curr_distance) {
- sched_domains_numa_distance[level++] = next_distance;
- sched_domains_numa_levels = level;
- curr_distance = next_distance;
- } else break;
- }
+ int distance = node_distance(0, j);
- /*
- * In case of sched_debug() we verify the above assumption.
- */
- if (!sched_debug())
- break;
+ if (distance > curr_distance &&
+ (distance < next_distance ||
+ next_distance == curr_distance))
+ next_distance = distance;
+
+ }
+ if (next_distance != curr_distance) {
+ sched_domains_numa_distance[level++] = next_distance;
+ sched_domains_numa_levels = level;
+ curr_distance = next_distance;
+ } else break;
}
/*
@@ -1428,7 +1427,24 @@ void sched_init_numa(void)
sched_domains_numa_masks[i][j] = mask;
for_each_node(k) {
- if (node_distance(j, k) > sched_domains_numa_distance[i])
+ int distance = node_distance(j, k);
+
+ if (!i && j != k) {
+ sched_numa_warn("Non-trace locality\n");
+ goto fail;
+ }
+
+ if (distance > curr_distance) {
+ sched_numa_warn("Node-0 not complete\n");
+ goto fail;
+ }
+
+ if (distance != node_distance(k, j)) {
+ sched_numa_warn("Non symmetric\n");
+ goto fail;
+ }
+
+ if (distance > sched_domains_numa_distance[i])
continue;
cpumask_or(mask, mask, cpumask_of_node(k));
@@ -1437,9 +1453,10 @@ void sched_init_numa(void)
}
/* Compute default topology size */
- for (i = 0; sched_domain_topology[i].mask; i++);
+ for (k = 0; sched_domain_topology[k].mask; k++)
+ ;
- tl = kzalloc((i + level + 1) *
+ tl = kzalloc((k + level + 1) *
sizeof(struct sched_domain_topology_level), GFP_KERNEL);
if (!tl)
return;
@@ -1447,7 +1464,7 @@ void sched_init_numa(void)
/*
* Copy the default topology bits..
*/
- for (i = 0; sched_domain_topology[i].mask; i++)
+ for (i = 0; i < k; i++)
tl[i] = sched_domain_topology[i];
/*
@@ -1478,6 +1495,31 @@ void sched_init_numa(void)
sched_max_numa_distance = sched_domains_numa_distance[level - 1];
init_numa_topology_type();
+
+ return;
+
+fail:
+ /* Compute default topology size */
+ for (k = 0; sched_domain_topology[k].mask; k++)
+ ;
+
+ tl = kzalloc((k + 2) *
+ sizeof(struct sched_domain_topology_level), GFP_KERNEL);
+ if (!tl)
+ return;
+
+ /*
+ * Copy the default topology bits..
+ */
+ for (i = 0; i < k; i++)
+ tl[i] = sched_domain_topology[i];
+
+ tl[i] = (struct sched_domain_topology_level){
+ .mask = cpu_system_mask,
+ SD_INIT_NAME(SYSTEM)
+ };
+
+ sched_domain_topology = tl;
}
void sched_domains_numa_masks_set(unsigned int cpu)
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