Re: [PATCH v2 2/2] mce: don't try to wake thread before it exists.

[Daniel Wagner <daniel.wagner@bmw-carit.de>]

On 03/06/2015 10:12 PM, Sebastian Andrzej Siewior wrote:
> * Sebastian Andrzej Siewior | 2015-03-06 22:01:27 [+0100]:
> 
>> We only miss a printk. The userland helper is not yet ready and we won't
>> anyone one waiting on the wait queue. So it should be enough to simply
>> check if the swait is ready.
> 
> So this should be enough and I fold this in you #1 patch. And now I see
> that swork_queue() might be called from hardirq context so it needs irqs
> off. I fix that one, too. But after that we should be good to go.

Thanks.

> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -1385,6 +1385,7 @@ static void __mce_notify_work(struct swo
>  }
>  
>  #ifdef CONFIG_PREEMPT_RT_FULL
> +static bool notify_work_ready __read_mostly;
>  static struct swork_event notify_work;
>  
>  static int mce_notify_work_init(void)
> @@ -1396,12 +1397,14 @@ static int mce_notify_work_init(void)
>  		return err;
>  
>  	INIT_SWORK(&notify_work, __mce_notify_work);
> +	notify_work_ready = true;
>  	return 0;
>  }

Stupid question: Couldn't the compiler or the CPU reorder the assignemnt
here? That is notify_work_ready is true before notify_work->func is set?

>  static void mce_notify_work(void)
>  {
> -	swork_queue(&notify_work);
> +	if (notify_work_ready)
> +		swork_queue(&notify_work);

Obviously, here the related question on the ordering.

Maybe I am a bit too paranoid after reading memory-barriers.txt a few times.

cheers,
daniel