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@xxxxxxx> Signed-off-by: Dawei Li <dawei.li@xxxxxxxxxxxx> --- drivers/perf/thunderx2_pmu.c | 10 +++------- 1 file changed, 3 insertions(+), 7 deletions(-) diff --git a/drivers/perf/thunderx2_pmu.c b/drivers/perf/thunderx2_pmu.c index e16d10c763de..b3377b662ffc 100644 --- a/drivers/perf/thunderx2_pmu.c +++ b/drivers/perf/thunderx2_pmu.c @@ -932,9 +932,8 @@ static int tx2_uncore_pmu_online_cpu(unsigned int cpu, static int tx2_uncore_pmu_offline_cpu(unsigned int cpu, struct hlist_node *hpnode) { - int new_cpu; struct tx2_uncore_pmu *tx2_pmu; - struct cpumask cpu_online_mask_temp; + unsigned int new_cpu; tx2_pmu = hlist_entry_safe(hpnode, struct tx2_uncore_pmu, hpnode); @@ -945,11 +944,8 @@ static int tx2_uncore_pmu_offline_cpu(unsigned int cpu, if (tx2_pmu->hrtimer_callback) hrtimer_cancel(&tx2_pmu->hrtimer); - cpumask_copy(&cpu_online_mask_temp, cpu_online_mask); - cpumask_clear_cpu(cpu, &cpu_online_mask_temp); - new_cpu = cpumask_any_and( - cpumask_of_node(tx2_pmu->node), - &cpu_online_mask_temp); + new_cpu = cpumask_any_and_but(cpumask_of_node(tx2_pmu->node), + cpu_online_mask, cpu); tx2_pmu->cpu = new_cpu; if (new_cpu >= nr_cpu_ids) -- 2.27.0