| From 92715e282be7c7488f892703c8d39b08976a833b Mon Sep 17 00:00:00 2001 |
| From: Ravikiran G Thirumalai <kiran@scalex86.org> |
| Date: Sat, 9 Dec 2006 21:33:35 +0100 |
| Subject: x86: Fix boot hang due to nmi watchdog init code |
| |
| 2.6.19 stopped booting (or booted based on build/config) on our x86_64 |
| systems due to a bug introduced in 2.6.19. check_nmi_watchdog schedules an |
| IPI on all cpus to busy wait on a flag, but fails to set the busywait |
| flag if NMI functionality is disabled. This causes the secondary cpus |
| to spin in an endless loop, causing the kernel bootup to hang. |
| Depending upon the build, the busywait flag got overwritten (stack variable) |
| and caused the kernel to bootup on certain builds. Following patch fixes |
| the bug by setting the busywait flag before returning from check_nmi_watchdog. |
| I guess using a stack variable is not good here as the calling function could |
| potentially return while the busy wait loop is still spinning on the flag. |
| |
| AK: I redid the patch significantly to be cleaner |
| |
| Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org> |
| Signed-off-by: Shai Fultheim <shai@scalex86.org> |
| Signed-off-by: Andi Kleen <ak@suse.de> |
| Signed-off-by: Chris Wright <chrisw@sous-sol.org> |
| --- |
| arch/i386/kernel/nmi.c | 8 ++++---- |
| arch/x86_64/kernel/nmi.c | 9 +++++---- |
| 2 files changed, 9 insertions(+), 8 deletions(-) |
| |
| --- linux-2.6.19.orig/arch/i386/kernel/nmi.c |
| +++ linux-2.6.19/arch/i386/kernel/nmi.c |
| @@ -192,6 +192,8 @@ static __cpuinit inline int nmi_known_cp |
| return 0; |
| } |
| |
| +static int endflag __initdata = 0; |
| + |
| #ifdef CONFIG_SMP |
| /* The performance counters used by NMI_LOCAL_APIC don't trigger when |
| * the CPU is idle. To make sure the NMI watchdog really ticks on all |
| @@ -199,7 +201,6 @@ static __cpuinit inline int nmi_known_cp |
| */ |
| static __init void nmi_cpu_busy(void *data) |
| { |
| - volatile int *endflag = data; |
| local_irq_enable_in_hardirq(); |
| /* Intentionally don't use cpu_relax here. This is |
| to make sure that the performance counter really ticks, |
| @@ -207,14 +208,13 @@ static __init void nmi_cpu_busy(void *da |
| pause instruction. On a real HT machine this is fine because |
| all other CPUs are busy with "useless" delay loops and don't |
| care if they get somewhat less cycles. */ |
| - while (*endflag == 0) |
| - barrier(); |
| + while (endflag == 0) |
| + mb(); |
| } |
| #endif |
| |
| static int __init check_nmi_watchdog(void) |
| { |
| - volatile int endflag = 0; |
| unsigned int *prev_nmi_count; |
| int cpu; |
| |
| --- linux-2.6.19.orig/arch/x86_64/kernel/nmi.c |
| +++ linux-2.6.19/arch/x86_64/kernel/nmi.c |
| @@ -190,6 +190,8 @@ void nmi_watchdog_default(void) |
| nmi_watchdog = NMI_IO_APIC; |
| } |
| |
| +static int endflag __initdata = 0; |
| + |
| #ifdef CONFIG_SMP |
| /* The performance counters used by NMI_LOCAL_APIC don't trigger when |
| * the CPU is idle. To make sure the NMI watchdog really ticks on all |
| @@ -197,7 +199,6 @@ void nmi_watchdog_default(void) |
| */ |
| static __init void nmi_cpu_busy(void *data) |
| { |
| - volatile int *endflag = data; |
| local_irq_enable_in_hardirq(); |
| /* Intentionally don't use cpu_relax here. This is |
| to make sure that the performance counter really ticks, |
| @@ -205,14 +206,13 @@ static __init void nmi_cpu_busy(void *da |
| pause instruction. On a real HT machine this is fine because |
| all other CPUs are busy with "useless" delay loops and don't |
| care if they get somewhat less cycles. */ |
| - while (*endflag == 0) |
| - barrier(); |
| + while (endflag == 0) |
| + mb(); |
| } |
| #endif |
| |
| int __init check_nmi_watchdog (void) |
| { |
| - volatile int endflag = 0; |
| int *counts; |
| int cpu; |
| |
| @@ -253,6 +253,7 @@ int __init check_nmi_watchdog (void) |
| if (!atomic_read(&nmi_active)) { |
| kfree(counts); |
| atomic_set(&nmi_active, -1); |
| + endflag = 1; |
| return -1; |
| } |
| endflag = 1; |