linux-kernel - Re: [PATCH] 2.6.28, vmalloc.c, vmap_page

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Date:	Sat, 27 Dec 2008 13:03:28 +0100
From:	Adam Lackorzynski <adam@...inf.tu-dresden.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: [PATCH] 2.6.28, vmalloc.c, vmap_page_range


On Fri Dec 26, 2008 at 16:39:46 -0800, Andrew Morton wrote:
> On Thu, 25 Dec 2008 22:02:35 +0100 Adam Lackorzynski <adam@...inf.tu-dresden.de> wrote:
> 
> > Hi,
> > 
> > in 2.6.28, the flush_cache_vmap in vmap_page_range() is called with the end of
> > the range twice. The following patch fixes this for me.
> > 
> 
> Did this bug have any observeable runtime effects?  If so, what were
> they?

Just in my own code, i.e. it doesn't have any effects to the kernel
itself.
 
> Well yeah.  This is what happens when functions modify their incoming
> arguments.  It's a bad programming practice which leads directly to
> exactly this sort of bug.
> 
> How about we fix that?

fine.

> --- a/mm/vmalloc.c~vmallocc-fix-flushing-in-vmap_page_range
> +++ a/mm/vmalloc.c
> @@ -151,11 +151,12 @@ static int vmap_pud_range(pgd_t *pgd, un
>   *
>   * Ie. pte at addr+N*PAGE_SIZE shall point to pfn corresponding to pages[N]
>   */
> -static int vmap_page_range(unsigned long addr, unsigned long end,
> +static int vmap_page_range(unsigned long start_addr, unsigned long end,
>  				pgprot_t prot, struct page **pages)
>  {
>  	pgd_t *pgd;
>  	unsigned long next;
> +	unsigned long addr = start_addr;
>  	int err = 0;
>  	int nr = 0;
>  
> @@ -167,7 +168,7 @@ static int vmap_page_range(unsigned long
>  		if (err)
>  			break;
>  	} while (pgd++, addr = next, addr != end);
> -	flush_cache_vmap(addr, end);
> +	flush_cache_vmap(start_addr, end);
>  
>  	if (unlikely(err))
>  		return err;

Adam
-- 
Adam                 adam@...inf.tu-dresden.de
  Lackorzynski         http://os.inf.tu-dresden.de/~adam/
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