[patch] ACPI, i686, x86_64: fix laptop bootup hang in init_acpi()

[Ingo Molnar <mingo@elte.hu>]

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.

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