Date:	Mon, 27 Sep 2010 12:44:26 +0200
From:	Robert Richter <robert.richter@....com>
To:	Huang Ying <ying.huang@...el.com>
CC:	Don Zickus <dzickus@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH -v2 7/7] x86, NMI, Remove do_nmi_callback logic

On 26.09.10 20:57:06, Huang Ying wrote:
> do_nmi_callback related logic is removed, because it is useless, just
> adds code complexity.
> 
> unknown_nmi_panic sysctl is reserved to keep kernel ABI unchanged.

"unknown_nmi_panic" and "panic_on_unrecovered_nmi" are different. See
below and also Documentation/sysctl/kernel.txt.

> 
> Signed-off-by: Huang Ying <ying.huang@...el.com>
> ---
>  arch/x86/include/asm/nmi.h    |   10 +++++++++-
>  arch/x86/kernel/apic/hw_nmi.c |    1 -
>  arch/x86/kernel/apic/nmi.c    |   29 +----------------------------
>  arch/x86/kernel/traps.c       |   16 ++++++++++------
>  4 files changed, 20 insertions(+), 36 deletions(-)
> 
> --- a/arch/x86/include/asm/nmi.h
> +++ b/arch/x86/include/asm/nmi.h
> @@ -30,9 +30,17 @@ extern void setup_apic_nmi_watchdog(void
>  extern void stop_apic_nmi_watchdog(void *);
>  extern void disable_timer_nmi_watchdog(void);
>  extern void enable_timer_nmi_watchdog(void);
> -extern int nmi_watchdog_tick(struct pt_regs *regs, unsigned reason);
>  extern void cpu_nmi_set_wd_enabled(void);
>  
> +#if defined(CONFIG_X86_LOCAL_APIC) && !defined(CONFIG_LOCKUP_DETECTOR)
> +extern int nmi_watchdog_tick(struct pt_regs *regs);
> +#else
> +static inline int nmi_watchdog_tick(struct pt_regs *regs)
> +{
> +	return 0;
> +}
> +#endif
> +
>  extern atomic_t nmi_active;
>  extern unsigned int nmi_watchdog;
>  #define NMI_NONE	0
> --- a/arch/x86/kernel/apic/hw_nmi.c
> +++ b/arch/x86/kernel/apic/hw_nmi.c
> @@ -100,7 +100,6 @@ void acpi_nmi_disable(void) { return; }
>  #endif
>  atomic_t nmi_active = ATOMIC_INIT(0);           /* oprofile uses this */
>  EXPORT_SYMBOL(nmi_active);
> -int unknown_nmi_panic;
>  void cpu_nmi_set_wd_enabled(void) { return; }
>  void stop_apic_nmi_watchdog(void *unused) { return; }
>  void setup_apic_nmi_watchdog(void *unused) { return; }
> --- a/arch/x86/kernel/apic/nmi.c
> +++ b/arch/x86/kernel/apic/nmi.c
> @@ -37,7 +37,6 @@
>  
>  #include <asm/mach_traps.h>
>  
> -int unknown_nmi_panic;
>  int nmi_watchdog_enabled;
>  
>  /* For reliability, we're prepared to waste bits here. */
> @@ -389,7 +388,7 @@ void touch_nmi_watchdog(void)
>  EXPORT_SYMBOL(touch_nmi_watchdog);
>  
>  notrace __kprobes int
> -nmi_watchdog_tick(struct pt_regs *regs, unsigned reason)
> +nmi_watchdog_tick(struct pt_regs *regs)
>  {
>  	/*
>  	 * Since current_thread_info()-> is always on the stack, and we
> @@ -483,23 +482,6 @@ static void disable_ioapic_nmi_watchdog(
>  	on_each_cpu(stop_apic_nmi_watchdog, NULL, 1);
>  }
>  
> -static int __init setup_unknown_nmi_panic(char *str)
> -{
> -	unknown_nmi_panic = 1;
> -	return 1;
> -}
> -__setup("unknown_nmi_panic", setup_unknown_nmi_panic);
> -
> -static int unknown_nmi_panic_callback(struct pt_regs *regs, int cpu)
> -{
> -	unsigned char reason = get_nmi_reason();
> -	char buf[64];
> -
> -	sprintf(buf, "NMI received for unknown reason %02x\n", reason);
> -	die_nmi(buf, regs, 1); /* Always panic here */
> -	return 0;

You are dropping this code that is different to panic().

> -}
> -
>  /*
>   * proc handler for /proc/sys/kernel/nmi
>   */
> @@ -540,15 +522,6 @@ int proc_nmi_enabled(struct ctl_table *t
>  
>  #endif /* CONFIG_SYSCTL */
>  
> -int do_nmi_callback(struct pt_regs *regs, int cpu)
> -{
> -#ifdef CONFIG_SYSCTL
> -	if (unknown_nmi_panic)
> -		return unknown_nmi_panic_callback(regs, cpu);
> -#endif
> -	return 0;
> -}
> -
>  void arch_trigger_all_cpu_backtrace(void)
>  {
>  	int i;
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -84,6 +84,7 @@ EXPORT_SYMBOL_GPL(used_vectors);
>  static int ignore_nmis;
>  
>  int unknown_nmi_for_hwerr;
> +int unknown_nmi_panic;
>  
>  /*
>   * Prevent NMI reason port (0x61) being accessed simultaneously, can
> @@ -308,6 +309,13 @@ gp_in_kernel:
>  	die("general protection fault", regs, error_code);
>  }
>  
> +static int __init setup_unknown_nmi_panic(char *str)
> +{
> +	unknown_nmi_panic = 1;

We should register a handler here for this case instead of using
global variables.

> +	return 1;
> +}
> +__setup("unknown_nmi_panic", setup_unknown_nmi_panic);
> +
>  static notrace __kprobes void
>  pci_serr_error(unsigned char reason, struct pt_regs *regs)
>  {
> @@ -385,7 +393,7 @@ unknown_nmi_error(unsigned char reason,
>  			reason, smp_processor_id());
>  
>  	printk(KERN_EMERG "Do you have a strange power saving mode enabled?\n");
> -	if (panic_on_unrecovered_nmi)
> +	if (unknown_nmi_panic || panic_on_unrecovered_nmi)
>  		panic("NMI: Not continuing");

There is different behavior, we should rather keep this code and add a
handler in the unknown_nmi_panic case with:

		die_nmi(...)
		...

-Robert

>  
>  	printk(KERN_EMERG "Dazed and confused, but trying to continue\n");
> @@ -432,12 +440,8 @@ static notrace __kprobes void default_do
>  	}
>  	raw_spin_unlock(&nmi_reason_lock);
>  
> -#if defined(CONFIG_X86_LOCAL_APIC) && !defined(CONFIG_LOCKUP_DETECTOR)
> -	if (nmi_watchdog_tick(regs, reason))
> -		return;
> -	if (do_nmi_callback(regs, smp_processor_id()))
> +	if (nmi_watchdog_tick(regs))
>  		return;
> -#endif
>  
>  	if (notify_die(DIE_NMIUNKNOWN, "nmi_unknown", regs, reason, 2, SIGINT)
>  	    == NOTIFY_STOP)
> --
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-- 
Advanced Micro Devices, Inc.
Operating System Research Center

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