[PATCH v2 06/10] perf/dwc_pcie: Avoid placing cpumask var on stack

Dawei Li
2024-04-03T12:54:19Z

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/dwc_pcie_pmu.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/perf/dwc_pcie_pmu.c b/drivers/perf/dwc_pcie_pmu.c
index 957058ad0099..c5e328f23841 100644
--- a/drivers/perf/dwc_pcie_pmu.c
+++ b/drivers/perf/dwc_pcie_pmu.c
@@ -690,9 +690,8 @@ static int dwc_pcie_pmu_offline_cpu(unsigned int cpu, struct hlist_node *cpuhp_n
{
struct dwc_pcie_pmu *pcie_pmu;
struct pci_dev *pdev;
- int node;
- cpumask_t mask;
unsigned int target;
+ int node;

pcie_pmu = hlist_entry_safe(cpuhp_node, struct dwc_pcie_pmu, cpuhp_node);
/* Nothing to do if this CPU doesn't own the PMU */
@@ -702,10 +701,9 @@ static int dwc_pcie_pmu_offline_cpu(unsigned int cpu, struct hlist_node *cpuhp_n
pcie_pmu->on_cpu = -1;
pdev = pcie_pmu->pdev;
node = dev_to_node(&pdev->dev);
- if (cpumask_and(&mask, cpumask_of_node(node), cpu_online_mask) &&
- cpumask_andnot(&mask, &mask, cpumask_of(cpu)))
- target = cpumask_any(&mask);
- else
+
+ target = cpumask_any_and_but(cpumask_of_node(node), 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