Re: [PATCH] fix vmstat per cpu usage

Jan Blunck
2006-08-02T13:30:09Z

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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

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---
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