From: Andrew Morton <akpm@osdl.org>

Cc: Andi Kleen <ak@muc.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Badari Pulavarty <pbadari@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 arch/i386/kernel/nmi.c   |    4 ++++
 arch/x86_64/kernel/nmi.c |    4 ++++
 2 files changed, 8 insertions(+)

diff -puN arch/i386/kernel/nmi.c~spinlock-debug-all-cpu-backtrace-fix arch/i386/kernel/nmi.c
--- a/arch/i386/kernel/nmi.c~spinlock-debug-all-cpu-backtrace-fix
+++ a/arch/i386/kernel/nmi.c
@@ -911,9 +911,13 @@ __kprobes int nmi_watchdog_tick(struct p
 	}
 
 	if (cpu_isset(cpu, backtrace_mask)) {
+		static DEFINE_SPINLOCK(lock);	/* Serialise the printks */
+
 		cpu_clear(cpu, backtrace_mask);
+		spin_lock(&lock);
 		printk("NMI backtrace for cpu %d\n", cpu);
 		dump_stack();
+		spin_unlock(&lock);
 	}
 
 	sum = per_cpu(irq_stat, cpu).apic_timer_irqs;
diff -puN arch/x86_64/kernel/nmi.c~spinlock-debug-all-cpu-backtrace-fix arch/x86_64/kernel/nmi.c
--- a/arch/x86_64/kernel/nmi.c~spinlock-debug-all-cpu-backtrace-fix
+++ a/arch/x86_64/kernel/nmi.c
@@ -804,9 +804,13 @@ int __kprobes nmi_watchdog_tick(struct p
 	}
 
 	if (cpu_isset(cpu, backtrace_mask)) {
+		static DEFINE_SPINLOCK(lock);	/* Serialise the printks */
+
 		cpu_clear(cpu, backtrace_mask);
+		spin_lock(&lock);
 		printk("NMI backtrace for cpu %d\n", cpu);
 		dump_stack();
+		spin_unlock(&lock);
 	}
 
 #ifdef CONFIG_X86_MCE
_