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From: Michal Hocko <mhocko@kernel.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	linux-next@vger.kernel.org, linux-kernel@vger.kernel.org,
	Zhangshaokun <zhangshaokun@hisilicon.com>
Subject: Re: [PATCH] mm: fix nodemask printing
Date: Mon, 20 Nov 2017 09:22:39 +0100
Message-ID: <20171120082239.irwzcrxkfu3qggbh@dhcp22.suse.cz> (raw)
In-Reply-To: <20171117101545.119689-1-arnd@arndb.de>

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

  reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-13  5:42 linux-next: build warning after merge of the akpm-current tree Stephen Rothwell
2017-11-13  8:09 ` Michal Hocko
2017-11-13  8:23   ` Michal Hocko
2017-11-13 11:43   ` Arnd Bergmann
2017-11-13 11:54     ` Michal Hocko
2017-11-13 12:24       ` Arnd Bergmann
2017-11-13 12:29       ` Michal Hocko
2017-11-16 22:44     ` Stephen Rothwell
2017-11-17  3:53       ` Stephen Rothwell
2017-11-17  9:36         ` Zhangshaokun
2017-11-17  9:56         ` Arnd Bergmann
2017-11-17 10:15           ` [PATCH] mm: fix nodemask printing Arnd Bergmann
2017-11-20  8:22             ` Michal Hocko [this message]
2017-11-20 11:33               ` Arnd Bergmann

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