2018-03-04 07:18:26

by Nick Desaulniers

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

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 <[email protected]>
---
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

2018-03-13 14:46:58

by Michal Hocko

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

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 <[email protected]>
> ---
> 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

2018-03-16 23:06:12

by Matthias Kaehlcke

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

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 <[email protected]>
> ---
> 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/