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 <[email protected]>
---
I've added some explicit tests for cpumask_weight() to make sure:
https://lore.kernel.org/all/[email protected]/
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
