[PATCH v2 08/10] perf/hisi_uncore: Avoid placing cpumask var on stack

Dawei Li
2024-04-03T12:54:27Z

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/hisilicon/hisi_uncore_pmu.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/perf/hisilicon/hisi_uncore_pmu.c b/drivers/perf/hisilicon/hisi_uncore_pmu.c
index 04031450d5fe..ccc9191ad1b6 100644
--- a/drivers/perf/hisilicon/hisi_uncore_pmu.c
+++ b/drivers/perf/hisilicon/hisi_uncore_pmu.c
@@ -504,7 +504,6 @@ int hisi_uncore_pmu_offline_cpu(unsigned int cpu, struct hlist_node *node)
{
struct hisi_pmu *hisi_pmu = hlist_entry_safe(node, struct hisi_pmu,
node);
- cpumask_t pmu_online_cpus;
unsigned int target;

if (!cpumask_test_and_clear_cpu(cpu, &hisi_pmu->associated_cpus))
@@ -518,9 +517,8 @@ int hisi_uncore_pmu_offline_cpu(unsigned int cpu, struct hlist_node *node)
hisi_pmu->on_cpu = -1;

/* Choose a new CPU to migrate ownership of the PMU to */
- cpumask_and(&pmu_online_cpus, &hisi_pmu->associated_cpus,
- cpu_online_mask);
- target = cpumask_any_but(&pmu_online_cpus, cpu);
+ target = cpumask_any_and_but(&hisi_pmu->associated_cpus,
+ cpu_online_mask, cpu);
if (target >= nr_cpu_ids)
return 0;

--
2.27.0