linux-kernel - Re: [PATCH linux-next] x86/mm: Fix compile warning in remove

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Date:	Wed, 6 Feb 2013 00:27:01 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Shuah Khan <shuah.khan@...com>
cc:	Andrew Morton <akpm@...ux-foundation.org>, tglx@...utronix.de,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	yinghai@...nel.org, tangchen@...fujitsu.com, wency@...fujitsu.com,
	linux-kernel@...r.kernel.org, x86@...nel.org, shuahkhan@...il.com
Subject: Re: [PATCH linux-next] x86/mm: Fix compile warning in
 remove_pagetable()

On Tue, 5 Feb 2013, Shuah Khan wrote:

> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 67bad4b..ed78400 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -987,7 +987,7 @@ remove_pud_table(pud_t *pud_start, unsigned long addr, unsigned long end,
>  static void __meminit
>  remove_pagetable(unsigned long start, unsigned long end, bool direct)
>  {
> -	unsigned long next;
> +	unsigned long next = pgd_addr_end(start, end);
>  	pgd_t *pgd;
>  	pud_t *pud;
>  	bool pgd_changed = false;

This isn't enough, there's a potential for an infinite loop if 
!pgd_present() is ever true in the iteration since "next" remains 
constant.  Theoretical, maybe.

I think it's better to just set next before checking for !pgd_present() in 
the iteration so it's clear what's happening.  Or, even better, change 
this into the standard do-while loop that everything else uses.
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