cpumask: fix CONFIG_CPUMASK_OFFSTACK=y cpu hotunplug crash

Impact: Fix cpu offline when CONFIG_MAXSMP=y

Changeset bc9b83dd1f66402b870301c3c7117b9c1484abb4 "cpumask: convert
c1e_mask in arch/x86/kernel/process.c to cpumask_var_t" contained a
bug: c1e_mask is manipulated even if C1E isn't detected (and hence
not allocated).

This is simply fixed by checking for NULL (which gcc optimizes out
anyway of CONFIG_CPUMASK_OFFSTACK=n, since it knows ce1_mask can never
be NULL).

In addition, fix a leak where select_idle_routine re-allocates
(and re-clears) c1e_mask on every cpu init.

Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Mike Travis <travis@sgi.com>
LKML-Reference: <200903171450.34549.rusty@rustcorp.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 13 insertions, 3 deletions

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index d794d9483c56..9874dd98a29f 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -733,6 +733,7 @@ static inline void __sti_mwait(unsigned long eax, unsigned long ecx)
 extern void mwait_idle_with_hints(unsigned long eax, unsigned long ecx);
 
 extern void select_idle_routine(const struct cpuinfo_x86 *c);
+extern void init_c1e_mask(void);
 
 extern unsigned long            boot_option_idle_override;
 extern unsigned long            idle_halt;
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 82f6cc045ad0..d7dd3c294e2a 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -812,6 +812,7 @@ static void vgetcpu_set_mode(void)
 void __init identify_boot_cpu(void)
 {
         identify_cpu(&boot_cpu_data);
+        init_c1e_mask();
 #ifdef CONFIG_X86_32
         sysenter_setup();
         enable_sep_cpu();
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 6638294cec8d..78533a519d8f 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -479,7 +479,8 @@ static int c1e_detected;
 
 void c1e_remove_cpu(int cpu)
 {
-        cpumask_clear_cpu(cpu, c1e_mask);
+        if (c1e_mask != NULL)
+                cpumask_clear_cpu(cpu, c1e_mask);
 }
 
 /*
@@ -556,13 +557,20 @@ void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
                 pm_idle = mwait_idle;
         } else if (check_c1e_idle(c)) {
                 printk(KERN_INFO "using C1E aware idle routine\n");
-                alloc_cpumask_var(&c1e_mask, GFP_KERNEL);
-                cpumask_clear(c1e_mask);
                 pm_idle = c1e_idle;
         } else
                 pm_idle = default_idle;
 }
 
+void __init init_c1e_mask(void)
+{
+        /* If we're using c1e_idle, we need to allocate c1e_mask. */
+        if (pm_idle == c1e_idle) {
+                alloc_cpumask_var(&c1e_mask, GFP_KERNEL);
+                cpumask_clear(c1e_mask);
+        }
+}
+
 static int __init idle_setup(char *str)
 {
         if (!str)