linux-kernel - Re: [git pull] vfs.git bits and pieces

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Date:	Wed, 20 Nov 2013 14:24:45 -0800
From:	Joe Perches <joe@...ches.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [git pull] vfs.git bits and pieces

On Wed, 2013-11-20 at 22:16 +0000, Al Viro wrote:
> While digging in the same area:
> 
> Wrong page freed on preallocate_pmds() failure exit
> 
> Note that pmds[i] is simply uninitialized at that point...
> Granted, it's very hard to hit (you need split page locks
> *and* kmalloc(sizeof(spinlock_t), GFP_KERNEL) failing),
> but the code is obviously bogus.
> 
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> ---
> diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
> index a7cccb6d..36aa999 100644
> --- a/arch/x86/mm/pgtable.c
> +++ b/arch/x86/mm/pgtable.c
> @@ -209,7 +209,7 @@ static int preallocate_pmds(pmd_t *pmds[])
>  		if (!pmd)
>  			failed = true;
>  		if (pmd && !pgtable_pmd_page_ctor(virt_to_page(pmd))) {
> -			free_page((unsigned long)pmds[i]);
> +			free_page((unsigned long)pmd);
>  			pmd = NULL;
>  			failed = true;
>  		}

trivia: It'd probably read better with an else too

		if (!pmd) {
			failed = true;
		} else if (!pgtable_pmd_page_ctor(virt_to_page(pmd))) {
			etc...

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