Re: [PATCH linux-next] powerpc: use raw_smp_processor_id in arch_touch_nmi_watchdog

[John Ogness]

On 2022-07-14, Zhouyi Zhou <zhouzho...@gmail.com> wrote:
> use raw_smp_processor_id() in arch_touch_nmi_watchdog
> because when called from watchdog, the cpu is preemptible.

I would expect the correct solution is to make it a non-migration
section. Something like the below (untested) patch.

John Ogness

diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c
index bfc27496fe7e..9d34aa809241 100644
--- a/arch/powerpc/kernel/watchdog.c
+++ b/arch/powerpc/kernel/watchdog.c
@@ -450,17 +450,23 @@ static enum hrtimer_restart watchdog_timer_fn(struct 
hrtimer *hrtimer)
 void arch_touch_nmi_watchdog(void)
 {
        unsigned long ticks = tb_ticks_per_usec * wd_timer_period_ms * 1000;
-       int cpu = smp_processor_id();
+       int cpu;
        u64 tb;
 
-       if (!cpumask_test_cpu(cpu, &watchdog_cpumask))
+       cpu = get_cpu();
+
+       if (!cpumask_test_cpu(cpu, &watchdog_cpumask)) {
+               goto out;
                return;
+       }
 
        tb = get_tb();
        if (tb - per_cpu(wd_timer_tb, cpu) >= ticks) {
                per_cpu(wd_timer_tb, cpu) = tb;
                wd_smp_clear_cpu_pending(cpu);
        }
+out:
+       put_cpu();
 }
 EXPORT_SYMBOL(arch_touch_nmi_watchdog);