x86/kexec: crash_vmclear_local_vmcss needs __rcu

This removes the sparse warning:
arch/x86/kernel/crash.c:49:32: sparse: incompatible types in comparison expression (different address spaces)

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/include/asm/kexec.h

@@ -163,7 +163,8 @@ struct kimage_arch {
 };
 #endif
 
-extern void (*crash_vmclear_loaded_vmcss)(void);
+typedef void crash_vmclear_fn(void);
+extern crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss;
 
 #endif /* __ASSEMBLY__ */
 

arch/x86/kernel/crash.c

@@ -38,12 +38,12 @@ int in_crash_kexec;
  *
  * protected by rcu.
  */
-void (*crash_vmclear_loaded_vmcss)(void) = NULL;
+crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss = NULL;
 EXPORT_SYMBOL_GPL(crash_vmclear_loaded_vmcss);
 
 static inline void cpu_crash_vmclear_loaded_vmcss(void)
 {
-	void (*do_vmclear_operation)(void) = NULL;
+	crash_vmclear_fn *do_vmclear_operation = NULL;
 
 	rcu_read_lock();
 	do_vmclear_operation = rcu_dereference(crash_vmclear_loaded_vmcss);