[PATCH] fix vmstat per cpu usage

[PATCH] fix vmstat per cpu usage

[Jan Blunck]

[-- Attachment #1: vmstat-fix.diff --]
[-- Type: text/x-patch, Size: 1271 bytes --]

From: Jan Blunck <jblunck@suse.de>
Subject: fix vmstat per cpu usage

The per cpu variables are used incorrectly in vmstat.h.

Signed-off-by: Jan Blunck <jblunck@suse.de>
---
 include/linux/vmstat.h |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Index: linux-v2.6.18-rc3/include/linux/vmstat.h
===================================================================
--- linux-v2.6.18-rc3.orig/include/linux/vmstat.h
+++ linux-v2.6.18-rc3/include/linux/vmstat.h
@@ -41,23 +41,23 @@ DECLARE_PER_CPU(struct vm_event_state, v
 
 static inline void __count_vm_event(enum vm_event_item item)
 {
-	__get_cpu_var(vm_event_states.event[item])++;
+	__get_cpu_var(vm_event_states).event[item]++;
 }
 
 static inline void count_vm_event(enum vm_event_item item)
 {
-	get_cpu_var(vm_event_states.event[item])++;
+	get_cpu_var(vm_event_states).event[item]++;
 	put_cpu();
 }
 
 static inline void __count_vm_events(enum vm_event_item item, long delta)
 {
-	__get_cpu_var(vm_event_states.event[item]) += delta;
+	__get_cpu_var(vm_event_states).event[item] += delta;
 }
 
 static inline void count_vm_events(enum vm_event_item item, long delta)
 {
-	get_cpu_var(vm_event_states.event[item]) += delta;
+	get_cpu_var(vm_event_states).event[item] += delta;
 	put_cpu();
 }
 

Re: [PATCH] fix vmstat per cpu usage

[Andrew Morton]

On Tue, 1 Aug 2006 19:36:21 +0200
Jan Blunck <jblunck@suse.de> wrote:

> The per cpu variables are used incorrectly in vmstat.h.
> 
> Signed-off-by: Jan Blunck <jblunck@suse.de>
> ---
>  include/linux/vmstat.h |    8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> Index: linux-v2.6.18-rc3/include/linux/vmstat.h
> ===================================================================
> --- linux-v2.6.18-rc3.orig/include/linux/vmstat.h
> +++ linux-v2.6.18-rc3/include/linux/vmstat.h
> @@ -41,23 +41,23 @@ DECLARE_PER_CPU(struct vm_event_state, v
>  
>  static inline void __count_vm_event(enum vm_event_item item)
>  {
> -	__get_cpu_var(vm_event_states.event[item])++;
> +	__get_cpu_var(vm_event_states).event[item]++;
>  }

How odd.  Are there any negative consequences to the existing code?

Re: [PATCH] fix vmstat per cpu usage

[Paul Mackerras]

Andrew Morton writes:

> On Tue, 1 Aug 2006 19:36:21 +0200
> Jan Blunck <jblunck@suse.de> wrote:
> 
> > The per cpu variables are used incorrectly in vmstat.h.
[snip]
> > -	__get_cpu_var(vm_event_states.event[item])++;
> > +	__get_cpu_var(vm_event_states).event[item]++;
> >  }
> 
> How odd.  Are there any negative consequences to the existing code?

That sort of thing - i.e. using __get_cpu_var on something which isn't
just a simple variable name - works with the current per-cpu macro
definitions, because they are pretty simple, but one can imagine other
reasonable implementations of __get_cpu_var which need the argument to
be a simple variable name.  I struck this when I was experimenting
with using __thread variables for per-cpu data.

Paul.

Re: [PATCH] fix vmstat per cpu usage

[Jan Blunck]

On Tue, Aug 01, Andrew Morton wrote:

> >  
> >  static inline void __count_vm_event(enum vm_event_item item)
> >  {
> > -	__get_cpu_var(vm_event_states.event[item])++;
> > +	__get_cpu_var(vm_event_states).event[item]++;
> >  }
> 
> How odd.  Are there any negative consequences to the existing code?

In asm-s390/percpu.h we use

 #define __get_cpu_var(var) __reloc_hide(var,S390_lowcore.percpu_offset)

and for modules on s390x __reloc_hide() is defined as

 #define __reloc_hide(var,offset) \
   (*({ unsigned long *__ptr; \
        asm ( "larl %0,per_cpu__"#var"@GOTENT" \
              : "=a" (__ptr) : "X" (per_cpu__##var) ); \
        (typeof(&per_cpu__##var))((*__ptr) + (offset)); }))

which leads in this case to

 larl %0, per_cpu__vm_event_states.event[item]@GOTENT

which is invalid asm.

Re: [PATCH] fix vmstat per cpu usage

[Jan Blunck]

[-- Attachment #1: Type: text/plain, Size: 200 bytes --]

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

[-- Attachment #2: percpu_var-error.diff --]
[-- Type: text/x-patch, Size: 2369 bytes --]

---
 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

Re: [PATCH] fix vmstat per cpu usage

[Andrew Morton]

On Wed, 2 Aug 2006 15:30:06 +0200
Jan Blunck <jblunck@suse.de> wrote:

> 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.
> 
> ...
> 
> 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]); }))

What's it do?  Forces a syntax error if `var' isn't a simple identifier?

Seems sane, although I'd check that the compiler doesn't accidentally
waste a stack slot for that local.  Perhaps it's be safer to make
it a non-existing function:

	extern int user_error#var(void);

Re: [PATCH] fix vmstat per cpu usage

[Jan Blunck]

[-- Attachment #1: Type: text/plain, Size: 732 bytes --]

On Wed, Aug 02, Andrew Morton wrote:

> > +#define per_cpu(var, cpu) (*({				\
> > +	int user_error_##var __attribute__ ((unused));	\
> > +	RELOC_HIDE(&per_cpu__##var, __per_cpu_offset[cpu]); }))
> 
> What's it do?  Forces a syntax error if `var' isn't a simple identifier?
> 
> Seems sane, although I'd check that the compiler doesn't accidentally
> waste a stack slot for that local.  Perhaps it's be safer to make
> it a non-existing function:
> 
> 	extern int user_error#var(void);
> 

Yes, that is even better. See attached patch with the modifications for my
major archs (s390, x86-64, generic). I did a run of 'make allmodconfig' with
the attached patch and it produced some errors. I'll send the patches in a
seperate mail.

[-- Attachment #2: percpu-simple-identifier-error.diff --]
[-- Type: text/x-patch, Size: 4443 bytes --]

From: Jan Blunck <jblunck@suse.de>
Subject: trigger a syntax error if percpu macros are incorrectly used

get_cpu_var()/per_cpu()/__get_cpu_var() arguments must be simple identifiers.
Otherwise the arch dependant implementations might break. This patch enforces
the correct usage of the macros by producing a syntax error if the variable is
not a simple identifier.

Signed-off-by: Jan Blunck <jblunck@suse.de>
---
 include/asm-generic/percpu.h |    4 +++-
 include/asm-s390/percpu.h    |   20 +++++++++++---------
 include/asm-x86_64/percpu.h  |   12 +++++++++---
 include/linux/percpu.h       |   10 ++++++++--
 4 files changed, 31 insertions(+), 15 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) (*({				\
+	extern int simple_indentifier_##var(void);	\
+	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
@@ -15,18 +15,20 @@
  */
 #if defined(__s390x__) && defined(MODULE)
 
-#define __reloc_hide(var,offset) \
-  (*({ unsigned long *__ptr; \
-       asm ( "larl %0,per_cpu__"#var"@GOTENT" \
-             : "=a" (__ptr) : "X" (per_cpu__##var) ); \
-       (typeof(&per_cpu__##var))((*__ptr) + (offset)); }))
+#define __reloc_hide(var,offset) (*({			\
+	extern int simple_indentifier_##var(void);	\
+	unsigned long *__ptr;				\
+	asm ( "larl %0,per_cpu__"#var"@GOTENT"		\
+	    : "=a" (__ptr) : "X" (per_cpu__##var) );	\
+	(typeof(&per_cpu__##var))((*__ptr) + (offset));	}))
 
 #else
 
-#define __reloc_hide(var, offset) \
-  (*({ unsigned long __ptr; \
-       asm ( "" : "=a" (__ptr) : "0" (&per_cpu__##var) ); \
-       (typeof(&per_cpu__##var)) (__ptr + (offset)); }))
+#define __reloc_hide(var, offset) (*({				\
+	extern int simple_indentifier_##var(void);		\
+	unsigned long __ptr;					\
+	asm ( "" : "=a" (__ptr) : "0" (&per_cpu__##var) );	\
+	(typeof(&per_cpu__##var)) (__ptr + (offset)); }))
 
 #endif
 
Index: linux-2.6/include/asm-x86_64/percpu.h
===================================================================
--- linux-2.6.orig/include/asm-x86_64/percpu.h
+++ linux-2.6/include/asm-x86_64/percpu.h
@@ -21,9 +21,15 @@
     __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 __get_cpu_var(var) (*RELOC_HIDE(&per_cpu__##var, __my_cpu_offset()))
-#define __raw_get_cpu_var(var) (*RELOC_HIDE(&per_cpu__##var, __my_cpu_offset()))
+#define per_cpu(var, cpu) (*({				\
+	extern int simple_indentifier_##var(void);	\
+	RELOC_HIDE(&per_cpu__##var, __per_cpu_offset(cpu)); }))
+#define __get_cpu_var(var) (*({				\
+	extern int simple_indentifier_##var(void);	\
+	RELOC_HIDE(&per_cpu__##var, __my_cpu_offset()); }))
+#define __raw_get_cpu_var(var) (*({			\
+	extern int simple_indentifier_##var(void);	\
+	RELOC_HIDE(&per_cpu__##var, __my_cpu_offset()); }))
 
 /* A macro to avoid #include hell... */
 #define percpu_modcopy(pcpudst, src, size)			\
Index: linux-2.6/include/linux/percpu.h
===================================================================
--- linux-2.6.orig/include/linux/percpu.h
+++ linux-2.6/include/linux/percpu.h
@@ -11,8 +11,14 @@
 #define PERCPU_ENOUGH_ROOM 32768
 #endif
 
-/* Must be an lvalue. */
-#define get_cpu_var(var) (*({ preempt_disable(); &__get_cpu_var(var); }))
+/*
+ * Must be an lvalue. Since @var must be a simple identifier,
+ * we force a syntax error here if it isn't.
+ */
+#define get_cpu_var(var) (*({				\
+	extern int simple_indentifier_##var(void);	\
+	preempt_disable();				\
+	&__get_cpu_var(var); }))
 #define put_cpu_var(var) preempt_enable()
 
 #ifdef CONFIG_SMP

Re: [PATCH] fix vmstat per cpu usage

[Steve Fox]

On Tue, 01 Aug 2006 19:36:21 +0200, Jan Blunck wrote:

> From: Jan Blunck <jblunck@suse.de>
> Subject: fix vmstat per cpu usage
> 
> The per cpu variables are used incorrectly in vmstat.h.
> 
> Signed-off-by: Jan Blunck <jblunck@suse.de>

This patch has allowed the first 2.6.18-rc* successful compilation on s390.

Andrew, please pull this into your tree too. Thanks.

Acked-by: Steve Fox <drfickle@us.ibm.com>

-- 

Steve Fox
IBM Linux Technology Center