path: root/arch/x86_64
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authorRavikiran G Thirumalai <kiran@scalex86.org>2006-12-09 21:33:35 +0100
committerAndi Kleen <andi@basil.nowhere.org>2006-12-09 21:33:35 +0100
commit92715e282be7c7488f892703c8d39b08976a833b (patch)
tree49acd962775f5a113483b16bbcc9c504728215ca /arch/x86_64
parent16d279d277aedd640d9dba5ddeb172b5e6bc7d75 (diff)
[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 <kiran@scalex86.org> Signed-off-by: Shai Fultheim <shai@scalex86.org> Signed-off-by: Andi Kleen <ak@suse.de>
Diffstat (limited to 'arch/x86_64')
1 files changed, 5 insertions, 4 deletions
diff --git a/arch/x86_64/kernel/nmi.c b/arch/x86_64/kernel/nmi.c
index 27e95e7922c1..186aebbae32d 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;
/* 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;
/* 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();
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)) {
atomic_set(&nmi_active, -1);
+ endflag = 1;
return -1;
endflag = 1;