cpumask: convert arch/x86/kernel/nmi.c's backtrace_mask to a cpumask_var_t

Impact: cleanup, reduce memory usage for CONFIG_CPUMASK_OFFSTACK=y

I *think* every path calls check_nmi_watchdog before using the
watchdog, so that's the right place for the initialization.

If that's wrong, we'll get a nice NULL-deref with
CONFIG_CPUMASK_OFFSTACK=y, and have uncovered another bug.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 6 insertions, 5 deletions

diff --git a/arch/x86/kernel/apic/nmi.c b/arch/x86/kernel/apic/nmi.c
index bdfad80c3cf1..d6bd62407152 100644
--- a/arch/x86/kernel/apic/nmi.c
+++ b/arch/x86/kernel/apic/nmi.c
@@ -39,7 +39,7 @@
 int unknown_nmi_panic;
 int nmi_watchdog_enabled;
 
-static cpumask_t backtrace_mask = CPU_MASK_NONE;
+static cpumask_var_t backtrace_mask;
 
 /* nmi_active:
  * >0: the lapic NMI watchdog is active, but can be disabled
@@ -138,6 +138,7 @@ int __init check_nmi_watchdog(void)
         if (!prev_nmi_count)
                 goto error;
 
+        alloc_cpumask_var(&backtrace_mask, GFP_KERNEL);
         printk(KERN_INFO "Testing NMI watchdog ... ");
 
 #ifdef CONFIG_SMP
@@ -413,14 +414,14 @@ nmi_watchdog_tick(struct pt_regs *regs, unsigned reason)
                 touched = 1;
         }
 
-        if (cpu_isset(cpu, backtrace_mask)) {
+        if (cpumask_test_cpu(cpu, backtrace_mask)) {
                 static DEFINE_SPINLOCK(lock);   /* Serialise the printks */
 
                 spin_lock(&lock);
                 printk(KERN_WARNING "NMI backtrace for cpu %d\n", cpu);
                 dump_stack();
                 spin_unlock(&lock);
-                cpu_clear(cpu, backtrace_mask);
+                cpumask_clear_cpu(cpu, backtrace_mask);
         }
 
         /* Could check oops_in_progress here too, but it's safer not to */
@@ -554,10 +555,10 @@ void __trigger_all_cpu_backtrace(void)
 {
         int i;
 
-        backtrace_mask = cpu_online_map;
+        cpumask_copy(backtrace_mask, cpu_online_mask);
         /* Wait for up to 10 seconds for all CPUs to do the backtrace */
         for (i = 0; i < 10 * 1000; i++) {
-                if (cpus_empty(backtrace_mask))
+                if (cpumask_empty(backtrace_mask))
                         break;
                 mdelay(1);
         }