On 2026-03-20 09:31, Mathieu Desnoyers wrote:
On 2026-03-20 09:21, Harry Yoo (Oracle) wrote:
On Fri, Mar 20, 2026 at 08:35:46AM -0400, Mathieu Desnoyers wrote:
On 2026-03-20 00:17, Harry Yoo wrote:
[...]
[1]: https://lore.kernel.org/20260227153730.1556542-4-
[email protected]/
@Mathieu: In patch 1/3 description,
Changes since v7:
- Explicitly initialize the subsystem from start_kernel() right
after mm_core_init() so it is up and running before the
creation of
the first mm at boot.
But how does this work when someone calls mm_cpumask() on init_mm
early?
Looks like it will behave incorrectly because get_rss_stat_items_size()
returns zero?
It doesn't work as expected at all. I missed that all users of
mm_cpumask()
end up relying on get_rss_stat_items_size(), which now calls
percpu_counter_tree_items_size(), which depends on initialization from
percpu_counter_tree_subsystem_init().
If you add a call to percpu_counter_tree_subsystem_init in
arch/powerpc/kernel/setup_arch() just before:
[...]
One thing we could do to catch this kind of init sequence issue
is to add a WARN_ON_ONCE in percpu_counter_tree_items_size:
size_t percpu_counter_tree_items_size(void)
{
if (WARN_ON_ONCE(!nr_cpus_order))
return 0;
return counter_config->nr_items * sizeof(struct
percpu_counter_tree_level_item);
}
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
