[PATCH 1/2] Revert "powerpc/xive: Fix the size of the cpumask used in xive_find_target_in_mask()"

Yury Norov
2026-03-19T03:37:26Z

This reverts commit a9dadc1c512807f955f0799e85830b420da47932.

The commit message states:

When called from xive_irq_startup(), the size of the cpumask can be
larger than nr_cpu_ids. This can result in a WARN_ON.
[...]
This happens because we're being called with our affinity mask set to
irq_default_affinity. That in turn was populated using
cpumask_setall(), which sets NR_CPUs worth of bits, not nr_cpu_ids
worth. Finally cpumask_weight() will return > nr_cpu_ids when passed a
mask which has > nr_cpu_ids bits set.

In modern kernel, cpumask_weight() can't return > nr_cpu_ids.

In inline case, cpumask_setall() explicitly clears all bits above
nr_cpu_ids, see commit 63355b9884b3 ("cpumask: be more careful with
'cpumask_setall()'"). So, despite that cpumask_weight() is passed
with small_cpumask_bits, which is NR_CPUS in this case, it can't
count over the nr_cpu_ids.

In outline case, cpumask_setall() may set bits beyond the limit up to
the next byte alignment, but in this case small_cpumask_bits is wired
to nr_cpu_ids, thus making overcounting impossible.

Signed-off-by: Yury Norov <ynorov@nvidia.com>
---

I've added some explicit tests for cpumask_weight() to make sure:
https://lore.kernel.org/all/20260319004349.849281-1-ynorov@nvidia.com/

arch/powerpc/sysdev/xive/common.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/sysdev/xive/common.c b/arch/powerpc/sysdev/xive/common.c
index e1a4f8a97393..e91ec9036ad8 100644
--- a/arch/powerpc/sysdev/xive/common.c
+++ b/arch/powerpc/sysdev/xive/common.c
@@ -551,7 +551,7 @@ static int xive_find_target_in_mask(const struct cpumask *mask,
int cpu, first, num, i;

/* Pick up a starting point CPU in the mask based on fuzz */
- num = min_t(int, cpumask_weight(mask), nr_cpu_ids);
+ num = cpumask_weight(mask);
first = fuzz % num;

/* Locate it */
--
2.43.0