diff --git a/[refs] b/[refs]
index 5a04ef537f98..6e61b157b05a 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 06c38d5e36b12d040839ff224e805146c0368556
+refs/heads/master: 2f537a9f8e82f55c241b002c8cfbf34303b45ada
diff --git a/trunk/arch/x86/kernel/apic/nmi.c b/trunk/arch/x86/kernel/apic/nmi.c
index d6bd62407152..2ba52f35a88c 100644
--- a/trunk/arch/x86/kernel/apic/nmi.c
+++ b/trunk/arch/x86/kernel/apic/nmi.c
@@ -414,7 +414,8 @@ nmi_watchdog_tick(struct pt_regs *regs, unsigned reason)
 		touched = 1;
 	}
 
-	if (cpumask_test_cpu(cpu, backtrace_mask)) {
+	/* We can be called before check_nmi_watchdog, hence NULL check. */
+	if (backtrace_mask != NULL && cpumask_test_cpu(cpu, backtrace_mask)) {
 		static DEFINE_SPINLOCK(lock);	/* Serialise the printks */
 
 		spin_lock(&lock);