Re: [PATCH] fix vmstat per cpu usage

[Jan Blunck]

Here comes another idea. To find further wrong usage of percpu variables I
wrote the following patch. It still needs some work for the other archs but
I'm interested in your feedback about that.

Jan
---
 include/asm-generic/percpu.h |    4 +++-
 include/asm-s390/percpu.h    |    6 ++++--
 include/linux/percpu.h       |    5 ++++-
 3 files changed, 11 insertions(+), 4 deletions(-)

Index: linux-2.6/include/asm-generic/percpu.h
===================================================================
--- linux-2.6.orig/include/asm-generic/percpu.h
+++ linux-2.6/include/asm-generic/percpu.h
@@ -14,7 +14,9 @@ extern unsigned long __per_cpu_offset[NR
     __attribute__((__section__(".data.percpu"))) __typeof__(type) per_cpu__##name
 
 /* var is in discarded region: offset to particular copy we want */
-#define per_cpu(var, cpu) (*RELOC_HIDE(&per_cpu__##var, __per_cpu_offset[cpu]))
+#define per_cpu(var, cpu) (*({				\
+	int user_error_##var __attribute__ ((unused));	\
+	RELOC_HIDE(&per_cpu__##var, __per_cpu_offset[cpu]); }))
 #define __get_cpu_var(var) per_cpu(var, smp_processor_id())
 #define __raw_get_cpu_var(var) per_cpu(var, raw_smp_processor_id())
 
Index: linux-2.6/include/asm-s390/percpu.h
===================================================================
--- linux-2.6.orig/include/asm-s390/percpu.h
+++ linux-2.6/include/asm-s390/percpu.h
@@ -16,7 +16,8 @@
 #if defined(__s390x__) && defined(MODULE)
 
 #define __reloc_hide(var,offset) \
-  (*({ unsigned long *__ptr; \
+  (*({ int user_error_##var __attribute__ ((unused)); \
+       unsigned long *__ptr; \
        asm ( "larl %0,per_cpu__"#var"@GOTENT" \
              : "=a" (__ptr) : "X" (per_cpu__##var) ); \
        (typeof(&per_cpu__##var))((*__ptr) + (offset)); }))
@@ -24,7 +25,8 @@
 #else
 
 #define __reloc_hide(var, offset) \
-  (*({ unsigned long __ptr; \
+  (*({ int user_error_##var __attribute__ ((unused)); \
+       unsigned long __ptr; \
        asm ( "" : "=a" (__ptr) : "0" (&per_cpu__##var) ); \
        (typeof(&per_cpu__##var)) (__ptr + (offset)); }))
 
Index: linux-2.6/include/linux/percpu.h
===================================================================
--- linux-2.6.orig/include/linux/percpu.h
+++ linux-2.6/include/linux/percpu.h
@@ -12,7 +12,10 @@
 #endif
 
 /* Must be an lvalue. */
-#define get_cpu_var(var) (*({ preempt_disable(); &__get_cpu_var(var); }))
+#define get_cpu_var(var) (*({				\
+	int user_error_##var __attribute__ ((unused));	\
+	preempt_disable();				\
+	&__get_cpu_var(var); }))
 #define put_cpu_var(var) preempt_enable()
 
 #ifdef CONFIG_SMP