[PATCH v2 02/10] perf/alibaba_uncore_drw: Avoid placing cpumask var on stack

Dawei Li
2024-04-03T12:53:24Z

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/alibaba_uncore_drw_pmu.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/drivers/perf/alibaba_uncore_drw_pmu.c b/drivers/perf/alibaba_uncore_drw_pmu.c
index a9277dcf90ce..d4d14b65c4a5 100644
--- a/drivers/perf/alibaba_uncore_drw_pmu.c
+++ b/drivers/perf/alibaba_uncore_drw_pmu.c
@@ -746,18 +746,14 @@ static int ali_drw_pmu_offline_cpu(unsigned int cpu, struct hlist_node *node)
struct ali_drw_pmu_irq *irq;
struct ali_drw_pmu *drw_pmu;
unsigned int target;
- int ret;
- cpumask_t node_online_cpus;

irq = hlist_entry_safe(node, struct ali_drw_pmu_irq, node);
if (cpu != irq->cpu)
return 0;

- ret = cpumask_and(&node_online_cpus,
- cpumask_of_node(cpu_to_node(cpu)), cpu_online_mask);
- if (ret)
- target = cpumask_any_but(&node_online_cpus, cpu);
- else
+ target = cpumask_any_and_but(cpumask_of_node(cpu_to_node(cpu)),
+ cpu_online_mask, cpu);
+ if (target >= nr_cpu_ids)
target = cpumask_any_but(cpu_online_mask, cpu);

if (target >= nr_cpu_ids)
--
2.27.0