[tip:x86/urgent] x86, NUMA: Fix fakenuma boot failure

From: tip-bot for KOSAKI Motohiro
Date: Fri Apr 15 2011 - 15:25:31 EST

Commit-ID: 7d6b46707f2491a94f4bd3b4329d2d7f809e9368
Gitweb: http://git.kernel.org/tip/7d6b46707f2491a94f4bd3b4329d2d7f809e9368
Author: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
AuthorDate: Fri, 15 Apr 2011 20:39:01 +0900
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Fri, 15 Apr 2011 20:28:19 +0200

x86, NUMA: Fix fakenuma boot failure

Currently, numa=fake boot parameter is broken. If it's used,
kernel may panic due to devide by zero error depending on CPU

Call Trace:
[<ffffffff8104ad4c>] find_busiest_group+0x38c/0xd30
[<ffffffff81086aff>] ? local_clock+0x6f/0x80
[<ffffffff81050533>] load_balance+0xa3/0x600
[<ffffffff81050f53>] idle_balance+0xf3/0x180
[<ffffffff81550092>] schedule+0x722/0x7d0
[<ffffffff81550538>] ? wait_for_common+0x128/0x190
[<ffffffff81550a65>] schedule_timeout+0x265/0x320
[<ffffffff81095815>] ? lock_release_holdtime+0x35/0x1a0
[<ffffffff81550538>] ? wait_for_common+0x128/0x190
[<ffffffff8109bb6c>] ? __lock_release+0x9c/0x1d0
[<ffffffff815534e0>] ? _raw_spin_unlock_irq+0x30/0x40
[<ffffffff815534e0>] ? _raw_spin_unlock_irq+0x30/0x40
[<ffffffff81550540>] wait_for_common+0x130/0x190
[<ffffffff81051920>] ? try_to_wake_up+0x510/0x510
[<ffffffff8155067d>] wait_for_completion+0x1d/0x20
[<ffffffff8107f36c>] kthread_create_on_node+0xac/0x150
[<ffffffff81077bb0>] ? process_scheduled_works+0x40/0x40
[<ffffffff8155045f>] ? wait_for_common+0x4f/0x190
[<ffffffff8107a283>] __alloc_workqueue_key+0x1a3/0x590
[<ffffffff81e0cce2>] cpuset_init_smp+0x6b/0x7b
[<ffffffff81df3d07>] kernel_init+0xc3/0x182
[<ffffffff8155d5e4>] kernel_thread_helper+0x4/0x10
[<ffffffff81553cd4>] ? retint_restore_args+0x13/0x13
[<ffffffff81df3c44>] ? start_kernel+0x400/0x400
[<ffffffff8155d5e0>] ? gs_change+0x13/0x13

The divede by zero is caused by the following line,

/* Adjust by relative CPU power of the group */
sgs->avg_load = (sgs->group_load * SCHED_LOAD_SCALE) / group->cpu_power;

This regression was caused by commit e23bba6044 ("x86-64, NUMA: Unify
emulated distance mapping") because it changes cpu -> node
mapping in the process of dropping fake_physnodes().

old) all cpus are assinged node 0
now) cpus are assigned round robin
(the logic is implemented by numa_init_array())

Note: The change in behavior only happens if the system doesn't
have neither ACPI SRAT table nor AMD northbridge NUMA

Round robin assignment doesn't work because init_numa_sched_groups_power()
assumes all logical cpus in the same physical cpu share the same node
(then it only accounts for group_first_cpu()), and the simple round robin
breaks the above assumption.

Thus, this patch implements a reassignment of node-ids if buggy firmware
or numa emulation makes wrong cpu node map. Tt enforce all logical cpus
in the same physical cpu share the same node.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Yinghai Lu <yinghai@xxxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxx>
Cc: Shaohui Zheng <shaohui.zheng@xxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20110415203928.1303.A69D9226@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
arch/x86/kernel/smpboot.c | 23 +++++++++++++++++++++++
1 files changed, 23 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index c2871d3..8ed8908 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -312,6 +312,26 @@ void __cpuinit smp_store_cpu_info(int id)

+static void __cpuinit check_cpu_siblings_on_same_node(int cpu1, int cpu2)
+ int node1 = early_cpu_to_node(cpu1);
+ int node2 = early_cpu_to_node(cpu2);
+ /*
+ * Our CPU scheduler assumes all logical cpus in the same physical cpu
+ * share the same node. But, buggy ACPI or NUMA emulation might assign
+ * them to different node. Fix it.
+ */
+ if (node1 != node2) {
+ pr_warning("CPU %d in node %d and CPU %d in node %d are in the same physical CPU. forcing same node %d\n",
+ cpu1, node1, cpu2, node2, node2);
+ numa_remove_cpu(cpu1);
+ numa_set_node(cpu1, node2);
+ numa_add_cpu(cpu1);
+ }
static void __cpuinit link_thread_siblings(int cpu1, int cpu2)
cpumask_set_cpu(cpu1, cpu_sibling_mask(cpu2));
@@ -320,6 +340,7 @@ static void __cpuinit link_thread_siblings(int cpu1, int cpu2)
cpumask_set_cpu(cpu2, cpu_core_mask(cpu1));
cpumask_set_cpu(cpu1, cpu_llc_shared_mask(cpu2));
cpumask_set_cpu(cpu2, cpu_llc_shared_mask(cpu1));
+ check_cpu_siblings_on_same_node(cpu1, cpu2);

@@ -361,10 +382,12 @@ void __cpuinit set_cpu_sibling_map(int cpu)
per_cpu(cpu_llc_id, cpu) == per_cpu(cpu_llc_id, i)) {
cpumask_set_cpu(i, cpu_llc_shared_mask(cpu));
cpumask_set_cpu(cpu, cpu_llc_shared_mask(i));
+ check_cpu_siblings_on_same_node(cpu, i);
if (c->phys_proc_id == cpu_data(i).phys_proc_id) {
cpumask_set_cpu(i, cpu_core_mask(cpu));
cpumask_set_cpu(cpu, cpu_core_mask(i));
+ check_cpu_siblings_on_same_node(cpu, i);
* Does this new cpu bringup a new core?
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