Say CPU 1 & CPU 2 are offlining, we will do in bulk cpu removal:
1. notifier callback (CPU_DOWN_PREPARE) on CPU 1
2. notifier callback (CPU_DOWN_PREPARE) on CPU 2
3. take_cpu_down CPU 1 & 2
4. notifier callback (CPU_DEAD) on CPU 1
5. notifier callback (CPU_DEAD) on CPU 2
The step 4 will settle down cpu domain according to new cpu_online_map. And
load balance could happen soon. Step 5 try to set this again and cause race.
This is a workaround for above issue.
Generally, this is because 'update_sched_domains' isn't a per-cpu callback, it
affects all cpus.
Signed-off-by: Shaohua Li <[email protected]>
---
linux-2.6.17-rc3-root/kernel/sched.c | 14 ++++++++++++--
1 files changed, 12 insertions(+), 2 deletions(-)
diff -puN kernel/sched.c~sched_domain_update_cpuhp kernel/sched.c
--- linux-2.6.17-rc3/kernel/sched.c~sched_domain_update_cpuhp 2006-05-07 07:45:32.000000000 +0800
+++ linux-2.6.17-rc3-root/kernel/sched.c 2006-05-07 07:45:32.000000000 +0800
@@ -6093,13 +6093,17 @@ void partition_sched_domains(cpumask_t *
* code, so we temporarily attach all running cpus to the NULL domain
* which will prevent rebalancing while the sched domains are recalculated.
*/
+static cpumask_t ready_sched_domains; /* FIXME: this is a hack */
static int update_sched_domains(struct notifier_block *nfb,
unsigned long action, void *hcpu)
{
switch (action) {
case CPU_UP_PREPARE:
case CPU_DOWN_PREPARE:
- detach_destroy_domains(&cpu_online_map);
+ if (!cpus_empty(ready_sched_domains)) {
+ detach_destroy_domains(&cpu_online_map);
+ cpus_clear(ready_sched_domains);
+ }
return NOTIFY_OK;
case CPU_UP_CANCELED:
@@ -6115,7 +6119,10 @@ static int update_sched_domains(struct n
}
/* The hotplug lock is already held by cpu_up/cpu_down */
- arch_init_sched_domains(&cpu_online_map);
+ if (!cpus_equal(ready_sched_domains, cpu_online_map)) {
+ arch_init_sched_domains(&cpu_online_map);
+ ready_sched_domains = cpu_online_map;
+ }
return NOTIFY_OK;
}
@@ -6125,6 +6132,9 @@ void __init sched_init_smp(void)
{
lock_cpu_hotplug();
arch_init_sched_domains(&cpu_online_map);
+#ifdef CONFIG_HOTPLUG_CPU
+ ready_sched_domains = cpu_online_map;
+#endif
unlock_cpu_hotplug();
/* XXX: Theoretical race here - CPU may be hotplugged now */
hotcpu_notifier(update_sched_domains, 0);
_