[PATCH v2 05/10] perf/arm_dsu: Avoid placing cpumask var on stack

Dawei Li
2024-04-03T12:53:45Z

For CONFIG_CPUMASK_OFFSTACK=y kernel, explicit allocation of cpumask
variable on stack is not recommended since it can cause potential stack
overflow.

Instead, kernel code should always use *cpumask_var API(s) to allocate
cpumask var in config-neutral way, leaving allocation strategy to
CONFIG_CPUMASK_OFFSTACK.

But dynamic allocation in cpuhp's teardown callback is somewhat problematic
for if allocation fails(which is unlikely but still possible):
- If -ENOMEM is returned to caller, kernel crashes for non-bringup
teardown;
- If callback pretends nothing happened and returns 0 to caller, it may
trap system into an in-consisitent/compromised state;

Use newly-introduced cpumask_any_and_but() to address all issues above.
It eliminates usage of temporary cpumask var in generic way, no matter how
the cpumask var is allocated.

Suggested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Dawei Li <dawei.li@shingroup.cn>
---
drivers/perf/arm_dsu_pmu.c | 19 ++++++-------------
1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/drivers/perf/arm_dsu_pmu.c b/drivers/perf/arm_dsu_pmu.c
index bae3ca37f846..adc0bbb5fafe 100644
--- a/drivers/perf/arm_dsu_pmu.c
+++ b/drivers/perf/arm_dsu_pmu.c
@@ -230,15 +230,6 @@ static const struct attribute_group *dsu_pmu_attr_groups[] = {
NULL,
};

-static int dsu_pmu_get_online_cpu_any_but(struct dsu_pmu *dsu_pmu, int cpu)
-{
- struct cpumask online_supported;
-
- cpumask_and(&online_supported,
- &dsu_pmu->associated_cpus, cpu_online_mask);
- return cpumask_any_but(&online_supported, cpu);
-}
-
static inline bool dsu_pmu_counter_valid(struct dsu_pmu *dsu_pmu, u32 idx)
{
return (idx < dsu_pmu->num_counters) ||
@@ -827,14 +818,16 @@ static int dsu_pmu_cpu_online(unsigned int cpu, struct hlist_node *node)

static int dsu_pmu_cpu_teardown(unsigned int cpu, struct hlist_node *node)
{
- int dst;
- struct dsu_pmu *dsu_pmu = hlist_entry_safe(node, struct dsu_pmu,
- cpuhp_node);
+ struct dsu_pmu *dsu_pmu;
+ unsigned int dst;
+
+ dsu_pmu = hlist_entry_safe(node, struct dsu_pmu, cpuhp_node);

if (!cpumask_test_and_clear_cpu(cpu, &dsu_pmu->active_cpu))
return 0;

- dst = dsu_pmu_get_online_cpu_any_but(dsu_pmu, cpu);
+ dst = cpumask_any_and_but(&dsu_pmu->associated_cpus,
+ cpu_online_mask, cpu);
/* If there are no active CPUs in the DSU, leave IRQ disabled */
if (dst >= nr_cpu_ids)
return 0;
--
2.27.0