From: Len Brown <len.brown@intel.com>
Reply-To: Len Brown <lenb@kernel.org>
Organization: Intel Open Source Technology Center
To: Ingo Molnar <mingo@elte.hu>
Subject: Re: [patch] ACPI, i686, x86_64: fix laptop bootup hang in init_acpi()
Date: Wed, 6 Dec 2006 18:57:29 -0500
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Cc: linux-kernel@vger.kernel.org, Andrew Morton <akpm@osdl.org>, ak@suse.de
References: <20061206223025.GA17227@elte.hu>
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On Wednesday 06 December 2006 17:30, Ingo Molnar wrote:
> Subject: [patch] ACPI, i686, x86_64: fix laptop bootup hang in init_acpi()
> From: Ingo Molnar <mingo@elte.hu>
> 
> during kernel bootup, a new T60 laptop (CoreDuo, 32-bit) hangs about 
> 10%-20% of the time in acpi_init():
> 
>  Calling initcall 0xc055ce1a: topology_init+0x0/0x2f()
>  Calling initcall 0xc055d75e: mtrr_init_finialize+0x0/0x2c()
>  Calling initcall 0xc05664f3: param_sysfs_init+0x0/0x175()
>  Calling initcall 0xc014cb65: pm_sysrq_init+0x0/0x17()
>  Calling initcall 0xc0569f99: init_bio+0x0/0xf4()
>  Calling initcall 0xc056b865: genhd_device_init+0x0/0x50()
>  Calling initcall 0xc056c4bd: fbmem_init+0x0/0x87()
>  Calling initcall 0xc056dd74: acpi_init+0x0/0x1ee()
> 
> it's a hard hang that not even an NMI could punch through! 
> Frustratingly, adding printks or function tracing to the ACPI code made 
> the hangs go away ...
> 
> after some time an additional detail emerged: disabling the NMI watchdog 
> made these occasional hangs go away.
> 
> So i spent the better part of today trying to debug this and trying out 
> various theories when i finally found the likely reason for the hang: if 
> acpi_ns_initialize_devices() executes an _INI AML method and an NMI 
> happens to hit that AML execution in the wrong moment, the machine would 
> hang.  (my theory is that this must be some sort of chipset setup method 
> doing stores to chipset mmio registers?)
> 
> Unfortunately given the characteristics of the hang it was sheer 
> impossible to figure out which of the numerous AML methods is impacted 
> by this problem.
> 
> as a workaround i wrote an interface to disable chipset-based NMIs while 
> executing _INI sections - and indeed this fixed the hang. I did a 
> boot-loop of 100 separate reboots and none hung - while without the 
> patch it would hang every 5-10 attempts. Out of caution i did not touch 
> the nmi_watchdog=2 case (it's not related to the chipset anyway and 
> didnt hang).
> 
> I implemented this for both x86_64 and i686, tested the i686 laptop both 
> with nmi_watchdog=1 [which triggered the hangs] and nmi_watchdog=2, and 
> tested an Athlon64 box with the 64-bit kernel as well. Everything builds 
> and works with the patch applied.

Good work root-causing this failure!

Personally I have never been a big fan of having the NMI watchdog
running by default on all systems -- but Andi insists that it helps him
debug failures, so tick it does...

Clearly this laptop was validated with Windows, and Windows doesn't
have this problem -- suggesting that we may be somewhat out on a limb...

Some alternatives to consider...
a. don't enable NMI watchdog by default
b. enable NMI watchdog, but later during kernel boot
    (assumption here that the issue is only during _INI)
c. disable the NMI whenever the ACPI interpeter is running
   (who knows, maybe this isn't limited to the _INI case, but
    could cause a hang at some other time -- only the
    BIOS AML writers knows....)

thoughts?
-Len

> Signed-off-by: Ingo Molnar <mingo@elte.hu>
> ---
>  arch/i386/kernel/nmi.c          |   28 ++++++++++++++++++++++++++++
>  arch/x86_64/kernel/nmi.c        |   27 +++++++++++++++++++++++++++
>  drivers/acpi/namespace/nsinit.c |    9 +++++++++
>  include/linux/nmi.h             |    9 ++++++++-
>  4 files changed, 72 insertions(+), 1 deletion(-)
> 
> Index: linux/arch/i386/kernel/nmi.c
> ===================================================================
> --- linux.orig/arch/i386/kernel/nmi.c
> +++ linux/arch/i386/kernel/nmi.c
> @@ -376,6 +376,34 @@ void enable_timer_nmi_watchdog(void)
>  	}
>  }
>  
> +static void __acpi_nmi_disable(void *__unused)
> +{
> +	apic_write_around(APIC_LVT0, APIC_DM_NMI | APIC_LVT_MASKED);
> +}
> +
> +/*
> + * Disable timer based NMIs on all CPUs:
> + */
> +void acpi_nmi_disable(void)
> +{
> +	if (atomic_read(&nmi_active) && nmi_watchdog == NMI_IO_APIC)
> +		on_each_cpu(__acpi_nmi_disable, NULL, 0, 1);
> +}
> +
> +static void __acpi_nmi_enable(void *__unused)
> +{
> +	apic_write_around(APIC_LVT0, APIC_DM_NMI);
> +}
> +
> +/*
> + * Enable timer based NMIs on all CPUs:
> + */
> +void acpi_nmi_enable(void)
> +{
> +	if (atomic_read(&nmi_active) && nmi_watchdog == NMI_IO_APIC)
> +		on_each_cpu(__acpi_nmi_enable, NULL, 0, 1);
> +}
> +
>  #ifdef CONFIG_PM
>  
>  static int nmi_pm_active; /* nmi_active before suspend */
> Index: linux/arch/x86_64/kernel/nmi.c
> ===================================================================
> --- linux.orig/arch/x86_64/kernel/nmi.c
> +++ linux/arch/x86_64/kernel/nmi.c
> @@ -360,6 +360,33 @@ void enable_timer_nmi_watchdog(void)
>  	}
>  }
>  
> +static void __acpi_nmi_disable(void *__unused)
> +{
> +	apic_write(APIC_LVT0, APIC_DM_NMI | APIC_LVT_MASKED);
> +}
> +
> +/*
> + * Disable timer based NMIs on all CPUs:
> + */
> +void acpi_nmi_disable(void)
> +{
> +	if (atomic_read(&nmi_active) && nmi_watchdog == NMI_IO_APIC)
> +		on_each_cpu(__acpi_nmi_disable, NULL, 0, 1);
> +}
> +
> +static void __acpi_nmi_enable(void *__unused)
> +{
> +	apic_write(APIC_LVT0, APIC_DM_NMI);
> +}
> +
> +/*
> + * Enable timer based NMIs on all CPUs:
> + */
> +void acpi_nmi_enable(void)
> +{
> +	if (atomic_read(&nmi_active) && nmi_watchdog == NMI_IO_APIC)
> +		on_each_cpu(__acpi_nmi_enable, NULL, 0, 1);
> +}
>  #ifdef CONFIG_PM
>  
>  static int nmi_pm_active; /* nmi_active before suspend */
> Index: linux/drivers/acpi/namespace/nsinit.c
> ===================================================================
> --- linux.orig/drivers/acpi/namespace/nsinit.c
> +++ linux/drivers/acpi/namespace/nsinit.c
> @@ -45,6 +45,7 @@
>  #include <acpi/acnamesp.h>
>  #include <acpi/acdispat.h>
>  #include <acpi/acinterp.h>
> +#include <linux/nmi.h>
>  
>  #define _COMPONENT          ACPI_NAMESPACE
>  ACPI_MODULE_NAME("nsinit")
> @@ -537,7 +538,15 @@ acpi_ns_init_one_device(acpi_handle obj_
>  	info->parameter_type = ACPI_PARAM_ARGS;
>  	info->flags = ACPI_IGNORE_RETURN_VALUE;
>  
> +	/*
> +	 * Some hardware relies on this being executed as atomically
> +	 * as possible (without an NMI being received in the middle of
> +	 * this) - so disable NMIs and initialize the device:
> +	 */
> +	acpi_nmi_disable();
>  	status = acpi_ns_evaluate(info);
> +	acpi_nmi_enable();
> +
>  	if (ACPI_SUCCESS(status)) {
>  		walk_info->num_INI++;
>  
> Index: linux/include/linux/nmi.h
> ===================================================================
> --- linux.orig/include/linux/nmi.h
> +++ linux/include/linux/nmi.h
> @@ -16,8 +16,15 @@
>   */
>  #ifdef ARCH_HAS_NMI_WATCHDOG
>  extern void touch_nmi_watchdog(void);
> +extern void acpi_nmi_disable(void);
> +extern void acpi_nmi_enable(void);
>  #else
> -# define touch_nmi_watchdog() touch_softlockup_watchdog()
> +static inline void touch_nmi_watchdog(void)
> +{
> +	touch_softlockup_watchdog();
> +}
> +static inline void acpi_nmi_disable(void) { }
> +static inline void acpi_nmi_enable(void) { }
>  #endif
>  
>  #endif
> -
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