x86: avoid theoretical spurious NMI backtraces with CONFIG_CPUMASK_OFFSTACK=y

In theory (though not shown in practice) alloc_cpumask_var() doesn't zero
memory, so CPUs might print an "NMI backtrace for cpu %d" once on boot.

(Bug introduced in fcef8576d8a64fc603e719c97d423f9f6d4e0e8b).

[ Impact: avoid theoretical syslog noise in rare configs ]

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <alpine.DEB.2.00.0904202113520.10097@gandalf.stny.rr.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/kernel/apic/nmi.c b/arch/x86/kernel/apic/nmi.c
index 2ba52f3..ce4fbfa 100644 (file)
--- a/arch/x86/kernel/apic/nmi.c
+++ b/arch/x86/kernel/apic/nmi.c
@@ -138,7 +138,7 @@ int __init check_nmi_watchdog(void)
        if (!prev_nmi_count)
                goto error;
 
-       alloc_cpumask_var(&backtrace_mask, GFP_KERNEL);
+       alloc_cpumask_var(&backtrace_mask, GFP_KERNEL|__GFP_ZERO);
        printk(KERN_INFO "Testing NMI watchdog ... ");
 
 #ifdef CONFIG_SMP