Re: [PATCH 2/5] kernel/watchdog_hld: clarify the condition in hardlockup_detector_event_create()

[Andrew Morton]

On Wed, 15 Sep 2021 11:51:00 +0800 Pingfan Liu <kernelfans@xxxxxxxxx> wrote:

> hardlockup_detector_event_create() indirectly calls
> kmem_cache_alloc_node(), which is blockable.
> 
> So here, the really planned context is is_percpu_thread().
> 
> ...
>
> --- a/kernel/watchdog_hld.c
> +++ b/kernel/watchdog_hld.c
> @@ -165,10 +165,13 @@ static void watchdog_overflow_callback(struct perf_event *event,
>  
>  static int hardlockup_detector_event_create(void)
>  {
> -	unsigned int cpu = smp_processor_id();
> +	unsigned int cpu;
>  	struct perf_event_attr *wd_attr;
>  	struct perf_event *evt;
>  
> +	/* This function plans to execute in cpu bound kthread */
> +	BUG_ON(!is_percpu_thread());

Can we avoid adding the BUG()?  Find a way to emit a WARNing and then
permit the kernel to continue?

> +	cpu = raw_smp_processor_id();
>  	wd_attr = &wd_hw_attr;
>  	wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);