Why are you cc'ing x86 and numa folks but not a single scheduler person
when you're patching scheduler stuff?
On Tue, 2012-09-18 at 18:12 +0800, Tang Chen wrote:
> Once array sched_domains_numa_masks is defined, it is never updated.
> When a new cpu on a new node is onlined,
Hmm, so there's hardware where you can boot with smaller nr_node_ids
than possible.. I guess that makes sense.
> the coincident member in
> sched_domains_numa_masks is not initialized, and all the masks are 0.
> As a result, the build_overlap_sched_groups() will initialize a NULL
> sched_group for the new cpu on the new node, which will lead to kernel panic.
<snip>
> This patch registers a new notifier for cpu hotplug notify chain, and
> updates sched_domains_numa_masks every time a new cpu is onlined or offlined.
Urgh, more hotplug notifiers.. a well.
> Signed-off-by: Tang Chen <tangchen@xxxxxxxxxxxxxx>
> ---
> kernel/sched/core.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 files changed, 62 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index fbf1fd0..66b36ab 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6711,6 +6711,14 @@ static void sched_init_numa(void)
> * numbers.
> */
>
> + /*
> + * Since sched_domains_numa_levels is also used in other functions as
> + * an index for sched_domains_numa_masks[][], we should reset it here in
> + * case sched_domains_numa_masks[][] fails to be initialized. And set it
> + * to 'level' when sched_domains_numa_masks[][] is fully initialized.
> + */
> + sched_domains_numa_levels = 0;
This isn't strictly needed for this patch right? I don't see anybody
calling sched_init_numa() a second time (although they should)..
> sched_domains_numa_masks = kzalloc(sizeof(void *) * level, GFP_KERNEL);
> if (!sched_domains_numa_masks)
> return;
> @@ -6765,11 +6773,64 @@ static void sched_init_numa(void)
> }
>
> sched_domain_topology = tl;
> +
> + sched_domains_numa_levels = level;
> +}
> +
> +static void sched_domains_numa_masks_set(int cpu)
> +{
> + int i, j;
> + int node = cpu_to_node(cpu);
> +
> + for (i = 0; i < sched_domains_numa_levels; i++)
> + for (j = 0; j < nr_node_ids; j++)
> + if (node_distance(j, node) <= sched_domains_numa_distance[i])
> + cpumask_set_cpu(cpu, sched_domains_numa_masks[i][j]);
> +}
> +
> +static void sched_domains_numa_masks_clear(int cpu)
> +{
> + int i, j;
> + for (i = 0; i < sched_domains_numa_levels; i++)
> + for (j = 0; j < nr_node_ids; j++)
> + cpumask_clear_cpu(cpu, sched_domains_numa_masks[i][j]);
> +}
Aside from the coding style nit of wanting braces over multi-line
statements even though not strictly required, I really don't see how
this could possibly be right..
We do this because nr_node_ids changed, right? This means the entire
distance table grew/shrunk, which means we should do the level scan
again.
> @@ -7218,6 +7279,7 @@ void __init sched_init_smp(void)
> mutex_unlock(&sched_domains_mutex);
> put_online_cpus();
>
> + hotcpu_notifier(sched_domains_numa_masks_update, CPU_PRI_SCHED_ACTIVE);
> hotcpu_notifier(cpuset_cpu_active, CPU_PRI_CPUSET_ACTIVE);
> hotcpu_notifier(cpuset_cpu_inactive, CPU_PRI_CPUSET_INACTIVE);
OK, so you really want your notifier to run before cpuset_cpu_active
because otherwise you get that crash, yet you fail with the whole order
thing.. You should not _ever_ rely on registration order.
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