Re: fix BUG: using smp_processor_id() in touch_nmi_watchdog and touch_softlockup_watchdog

[Peter Zijlstra <peterz@infradead.org>]

On Fri, 2010-08-13 at 13:21 +0300, Sergey Senozhatsky wrote:

> [   67.703556] BUG: using smp_processor_id() in preemptible [00000000] code: s2disk/5139
> [   67.703563] caller is touch_nmi_watchdog+0x15/0x2c
> [   67.703566] Pid: 5139, comm: s2disk Not tainted 2.6.36-rc0-git12-07921-g60bf26a-dirty #116
> [   67.703568] Call Trace:
> [   67.703575]  [<ffffffff811f6bf1>] debug_smp_processor_id+0xc9/0xe4
> [   67.703578]  [<ffffffff81092766>] touch_nmi_watchdog+0x15/0x2c
> [   67.703584]  [<ffffffff81222950>] acpi_os_stall+0x34/0x40
> [   67.703589]  [<ffffffff812398d2>] acpi_ex_system_do_stall+0x34/0x38

Which could mean two things, either ACPI got funny on us, or Don's new
watchdog stuff has a hole in it.


> ---
> 
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index 613bc1f..8822f1e 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -116,13 +116,14 @@ static unsigned long get_sample_period(void)
>  static void __touch_watchdog(void)
>  {
>  	int this_cpu = smp_processor_id();
> -
> -	__get_cpu_var(watchdog_touch_ts) = get_timestamp(this_cpu);
> +	per_cpu(watchdog_touch_ts, this_cpu) = get_timestamp(this_cpu);
>  }

That change seems sensible enough..

>  void touch_softlockup_watchdog(void)
>  {
> -	__get_cpu_var(watchdog_touch_ts) = 0;
> +	int this_cpu = get_cpu();
> +	per_cpu(watchdog_touch_ts, this_cpu) = 0;
> +	put_cpu();
>  }
>  EXPORT_SYMBOL(touch_softlockup_watchdog);
>  
> @@ -142,7 +143,9 @@ void touch_all_softlockup_watchdogs(void)
>  #ifdef CONFIG_HARDLOCKUP_DETECTOR
>  void touch_nmi_watchdog(void)
>  {
> -	__get_cpu_var(watchdog_nmi_touch) = true;
> +	int this_cpu = get_cpu();
> +	per_cpu(watchdog_nmi_touch, this_cpu) = true;
> +	put_cpu();
>  	touch_softlockup_watchdog();
>  }
>  EXPORT_SYMBOL(touch_nmi_watchdog);

These other two really are about assumptions we make on the call sites,
which at the very least are violated by ACPI.

Don/Ingo, remember if we require touch_*_watchdog callers to have
preemption disabled? Or is the proposed patch sensible?