Subject: Re: linux-next: build warning after merge of the akpm-current tree

From: Michal Hocko <[email-masked]>
Date: Mon, 13 Nov 2017 09:09:55 +0100

On Mon 13-11-17 16:42:06, Stephen Rothwell wrote:
> Hi Andrew,
> 
> After merging the akpm-current tree, today's linux-next build (powerpc
> ppc64_defconfig) produced this warning:
> 
> In file included from include/linux/mmzone.h:17:0,
>                  from include/linux/mempolicy.h:10,
>                  from mm/mempolicy.c:70:
> mm/mempolicy.c: In function 'mpol_to_str':
> include/linux/nodemask.h:107:41: warning: the address of 'nodes' will always evaluate as 'true' [-Waddress]
>  #define nodemask_pr_args(maskp) (maskp) ? MAX_NUMNODES : 0, (maskp) ? (maskp)->bits : NULL
>                                          ^
> mm/mempolicy.c:2817:11: note: in expansion of macro 'nodemask_pr_args'
>            nodemask_pr_args(&nodes));
>            ^

Hmm, this warning is quite surprising to me. Sure in this particular
case maskp will always be non-NULL so we always expand to
	MAX_NUMNODES, maskp->bits
which is what we want. But we have other users which may be NULL. Does
anybody understan why this warns at all?
-- 
Michal Hocko
SUSE Labs