[kvm-unit-tests PATCH 2/2] lib/on-cpus: Fix on_cpumask

Andrew Jones
2024-10-23T13:17:30Z

on_cpumask should wait until the cpus in the mask, not including
the calling cpu, are idle. Checking the weight against nr_cpus
minus 1 only works when the mask is the same as the present mask.

Fixes: d012cfd5d309 ("lib/on-cpus: Introduce on_cpumask and on_cpumask_async")
Signed-off-by: Andrew Jones <andrew.jones@linux.dev>
---
lib/cpumask.h | 14 ++++++++++++++
lib/on-cpus.c | 17 ++++++++---------
2 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/lib/cpumask.h b/lib/cpumask.h
index e1e92aacd1f1..37d360786573 100644
--- a/lib/cpumask.h
+++ b/lib/cpumask.h
@@ -58,6 +58,20 @@ static inline void cpumask_clear(cpumask_t *mask)
memset(mask, 0, sizeof(*mask));
}

+/* true if src1 is a subset of src2 */
+static inline bool cpumask_subset(const struct cpumask *src1, const struct cpumask *src2)
+{
+ unsigned long lastmask = BIT_MASK(nr_cpus) - 1;
+ int i;
+
+ for (i = 0; i < BIT_WORD(nr_cpus); ++i) {
+ if (cpumask_bits(src1)[i] & ~cpumask_bits(src2)[i])
+ return false;
+ }
+
+ return !lastmask || !((cpumask_bits(src1)[i] & ~cpumask_bits(src2)[i]) & lastmask);
+}
+
static inline bool cpumask_empty(const cpumask_t *mask)
{
unsigned long lastmask = BIT_MASK(nr_cpus) - 1;
diff --git a/lib/on-cpus.c b/lib/on-cpus.c
index f6072117fa1b..7ce58be0e7e9 100644
--- a/lib/on-cpus.c
+++ b/lib/on-cpus.c
@@ -126,24 +126,23 @@ void on_cpumask_async(const cpumask_t *mask, void (*func)(void *data), void *dat
void on_cpumask(const cpumask_t *mask, void (*func)(void *data), void *data)
{
int cpu, me = smp_processor_id();
+ cpumask_t tmp;

- for_each_cpu(cpu, mask) {
- if (cpu == me)
- continue;
+ cpumask_copy(&tmp, mask);
+ cpumask_clear_cpu(me, &tmp);
+
+ for_each_cpu(cpu, &tmp)
on_cpu_async(cpu, func, data);
- }
if (cpumask_test_cpu(me, mask))
func(data);

- for_each_cpu(cpu, mask) {
- if (cpu == me)
- continue;
+ for_each_cpu(cpu, &tmp) {
cpumask_set_cpu(me, &on_cpu_info[cpu].waiters);
deadlock_check(me, cpu);
}
- while (cpumask_weight(&cpu_idle_mask) < nr_cpus - 1)
+ while (!cpumask_subset(&tmp, &cpu_idle_mask))
smp_wait_for_event();
- for_each_cpu(cpu, mask)
+ for_each_cpu(cpu, &tmp)
cpumask_clear_cpu(me, &on_cpu_info[cpu].waiters);
}

--
2.47.0