A question of perf NMI handler

Lin Ming
2010-08-04T09:21:07Z

With nmi_watchdog enabled, perf_event_nmi_handler always return
NOTIFY_STOP(active_events > 0), and the notifier call chain will not
call further.

If it was not perf NMI, does the perf nmi handler may stop the real NMI
handler get called because NOTIFY_STOP is returned??

static int __kprobes
perf_event_nmi_handler(struct notifier_block *self,
unsigned long cmd, void *__args)
{
struct die_args *args = __args;
struct pt_regs *regs;

if (!atomic_read(&active_events)) ===> With nmi_watchdog enabled, active_events > 0
return NOTIFY_DONE;

switch (cmd) {
case DIE_NMI:
case DIE_NMI_IPI:
break;

default:
return NOTIFY_DONE;
}

regs = args->regs;

apic_write(APIC_LVTPC, APIC_DM_NMI);
/*
* Can't rely on the handled return value to say it was our NMI, two
* events could trigger 'simultaneously' raising two back-to-back NMIs.
*
* If the first NMI handles both, the latter will be empty and daze
* the CPU.
*/
x86_pmu.handle_irq(regs);

return NOTIFY_STOP;
}

Thanks,
Lin Ming