From 92715e282be7c7488f892703c8d39b08976a833b Mon Sep 17 00:00:00 2001 From: Ravikiran G Thirumalai Date: Sat, 9 Dec 2006 21:33:35 +0100 Subject: [PATCH] [PATCH] 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 Signed-off-by: Shai Fultheim Signed-off-by: Andi Kleen --- arch/i386/kernel/nmi.c | 8 ++++---- arch/x86_64/kernel/nmi.c | 9 +++++---- 2 files changed, 9 insertions(+), 8 deletions(-) diff --git a/arch/i386/kernel/nmi.c b/arch/i386/kernel/nmi.c index f5bc7e1be8..a5e34d6559 100644 --- a/arch/i386/kernel/nmi.c +++ b/arch/i386/kernel/nmi.c @@ -195,6 +195,8 @@ static __cpuinit inline int nmi_known_cpu(void) 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 @@ -202,7 +204,6 @@ static __cpuinit inline int nmi_known_cpu(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, @@ -210,14 +211,13 @@ static __init void nmi_cpu_busy(void *data) 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; diff --git a/arch/x86_64/kernel/nmi.c b/arch/x86_64/kernel/nmi.c index 27e95e7922..186aebbae3 100644 --- a/arch/x86_64/kernel/nmi.c +++ b/arch/x86_64/kernel/nmi.c @@ -193,6 +193,8 @@ 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 @@ -200,7 +202,6 @@ 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, @@ -208,14 +209,13 @@ static __init void nmi_cpu_busy(void *data) 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; @@ -256,6 +256,7 @@ int __init check_nmi_watchdog (void) if (!atomic_read(&nmi_active)) { kfree(counts); atomic_set(&nmi_active, -1); + endflag = 1; return -1; } endflag = 1; -- 2.20.1