[PATCH] memory-failure: fix section mismatch

[PATCH] memory-failure: fix section mismatch

[Nick Desaulniers]

Clang complains when a variable is declared extern twice, but with two
different sections. num_poisoned_pages is marked extern and __read_mostly
in include/linux/swapops.h, but only extern in include/linux/mm.h. Some
c source files must include both, and thus see the conflicting
declarations.

Signed-off-by: Nick Desaulniers <nick.desaulniers@gmail.com>
---
 include/linux/mm.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ad06d42adb1a..bd4bd59f02c1 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2582,7 +2582,7 @@ extern int get_hwpoison_page(struct page *page);
 extern int sysctl_memory_failure_early_kill;
 extern int sysctl_memory_failure_recovery;
 extern void shake_page(struct page *p, int access);
-extern atomic_long_t num_poisoned_pages;
+extern atomic_long_t num_poisoned_pages __read_mostly;
 extern int soft_offline_page(struct page *page, int flags);
 
 
-- 
2.14.1

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Re: [PATCH] memory-failure: fix section mismatch

[Michal Hocko]

On Sat 03-03-18 23:16:11, Nick Desaulniers wrote:
> Clang complains when a variable is declared extern twice, but with two
> different sections. num_poisoned_pages is marked extern and __read_mostly
> in include/linux/swapops.h, but only extern in include/linux/mm.h. Some
> c source files must include both, and thus see the conflicting
> declarations.

Why do we need declarations in both places? This sounds like a mess to
me.

> Signed-off-by: Nick Desaulniers <nick.desaulniers@gmail.com>
> ---
>  include/linux/mm.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index ad06d42adb1a..bd4bd59f02c1 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2582,7 +2582,7 @@ extern int get_hwpoison_page(struct page *page);
>  extern int sysctl_memory_failure_early_kill;
>  extern int sysctl_memory_failure_recovery;
>  extern void shake_page(struct page *p, int access);
> -extern atomic_long_t num_poisoned_pages;
> +extern atomic_long_t num_poisoned_pages __read_mostly;
>  extern int soft_offline_page(struct page *page, int flags);
>  
>  
> -- 
> 2.14.1
> 

-- 
Michal Hocko
SUSE Labs

Re: [PATCH] memory-failure: fix section mismatch

[Matthias Kaehlcke]

El Sat, Mar 03, 2018 at 11:16:11PM -0800 Nick Desaulniers ha dit:

> Clang complains when a variable is declared extern twice, but with two
> different sections. num_poisoned_pages is marked extern and __read_mostly
> in include/linux/swapops.h, but only extern in include/linux/mm.h. Some
> c source files must include both, and thus see the conflicting
> declarations.
> 
> Signed-off-by: Nick Desaulniers <nick.desaulniers@gmail.com>
> ---
>  include/linux/mm.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index ad06d42adb1a..bd4bd59f02c1 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2582,7 +2582,7 @@ extern int get_hwpoison_page(struct page *page);
>  extern int sysctl_memory_failure_early_kill;
>  extern int sysctl_memory_failure_recovery;
>  extern void shake_page(struct page *p, int access);
> -extern atomic_long_t num_poisoned_pages;
> +extern atomic_long_t num_poisoned_pages __read_mostly;
>  extern int soft_offline_page(struct page *page, int flags);

An equivalent patch was posted by Guenter Roeck and has been picked up
by Andrew: https://patchwork.kernel.org/patch/10243919/