linux-kernel - Re: [PATCH] mm: fix potential build error in compaction.h

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Message-ID: <20190213130010.GJ4525@dhcp22.suse.cz>
Date:   Wed, 13 Feb 2019 14:00:10 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: fix potential build error in compaction.h

On Tue 12-02-19 16:38:58, Yu Zhao wrote:
> On Tue, Feb 12, 2019 at 01:03:58PM +0100, Michal Hocko wrote:
> > On Fri 08-02-19 01:04:37, Yu Zhao wrote:
> > > Declaration of struct node is required regardless. On UMA system,
> > > including compaction.h without proceeding node.h shouldn't cause
> > > build error.
> > 
> > Anybody requiring struct node shouldn't depend on compaction.h to get
> > the declaration.
> 
> Yes, but the problem is the other way around. Build error happens
> when somebody includes compaction.h without definition or
> declaration of struct node, if CONFIG_NUMA is not set.
> 
> compaction.h already has struct node declaration to avoid the error
> when CONFIG_NUMA is set, but we need it for both cases.
> 
> > Anyway have you seen an actual build breakage?
> 
> Yes. I ran into the problem while trying to include compaction.h
> in this order, and had to move it to the bottom as a workaround.
> 
> #include <linux/backing-dev.h>
> #include <linux/compaction.h>
> #include <linux/ctype.h>
> #include <linux/freezer.h>
> #include <linux/hugetlb.h>
> #include <linux/kstaled.h>
> #include <linux/kthread.h>
> #include <linux/mm_inline.h>
> #include <linux/mm_types.h>
> #include <linux/module.h>
> #include <linux/pagemap.h>
> #include <linux/sched/task_stack.h>
> #include <linux/swap.h>

OK, fair enough. A subtle header file ordering dependencies are PITA.

Acked-by: Michal Hocko <mhocko@...e.com>

-- 
Michal Hocko
SUSE Labs