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SubjectRe: [PATCH] mm: fix nodemask printing
On Fri 17-11-17 11:15:45, Arnd Bergmann wrote:
> The cleanup caused build warnings for constant mask pointers:
>
> mm/mempolicy.c: In function ‘mpol_to_str’:
> ./include/linux/nodemask.h:108:11: warning: the comparison will always evaluate as ‘true’ for the address of ‘nodes’ will never be NULL [-Waddress]
>
> An earlier workaround I suggested was incorporated in the version that
> got merged, but that only solved the problem for gcc-7 and higher, while
> gcc-4.6 through gcc-6.x still warn.
>
> This changes the printing again to use inline functions that make it
> clear to the compiler that the line that does the NULL check has no
> idea whether the argument is a constant NULL.
>
> Fixes: 0205f75571e3 ("mm: simplify nodemask printing")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Thanks for the fixup. It is sad how a questionable warning makes the
code worse... Does it make sense to have the warning enabled?
Gcc bug [1] suggests there is no great interest into fixing it.

Anyway to the patch
Acked-by: Michal Hocko <mhocko@suse.com>

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82963

> ---
> I've done only minimal build testing on this, but did check it with
> all compiler versions this time.
> ---
> include/linux/nodemask.h | 13 ++++++++++---
> 1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h
> index 15cab3967d6d..1fbde8a880d9 100644
> --- a/include/linux/nodemask.h
> +++ b/include/linux/nodemask.h
> @@ -104,9 +104,16 @@ extern nodemask_t _unused_nodemask_arg_;
> *
> * Can be used to provide arguments for '%*pb[l]' when printing a nodemask.
> */
> -#define nodemask_pr_args(maskp) \
> - ((maskp) != NULL) ? MAX_NUMNODES : 0, \
> - ((maskp) != NULL) ? (maskp)->bits : NULL
> +#define nodemask_pr_args(maskp) __nodemask_pr_numnodes(maskp), \
> + __nodemask_pr_bits(maskp)
> +static inline unsigned int __nodemask_pr_numnodes(const nodemask_t *m)
> +{
> + return m ? MAX_NUMNODES : 0;
> +}
> +static inline const unsigned long *__nodemask_pr_bits(const nodemask_t *m)
> +{
> + return m ? m->bits : NULL;
> +}
>
> /*
> * The inline keyword gives the compiler room to decide to inline, or
> --
> 2.9.0

--
Michal Hocko
SUSE Labs

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