linux-kernel - Re: [PATCHv9-rebased2 05/37] khugepaged: recheck pmd after mmap

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20160616114603.GA19710@gezgin>
Date:	Thu, 16 Jun 2016 14:47:14 +0300
From:	Ebru Akagunduz <ebru.akagunduz@...il.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Hugh Dickins <hughd@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Dave Hansen <dave.hansen@...el.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Jerome Marchand <jmarchan@...hat.com>,
	Yang Shi <yang.shi@...aro.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Andres Lagar-Cavilla <andreslc@...gle.com>,
	Ning Qu <quning@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	sergey.senozhatsky.work@...il.com
Subject: Re: [PATCHv9-rebased2 05/37] khugepaged: recheck pmd after mmap_sem
 re-acquired

On Wed, Jun 15, 2016 at 11:06:10PM +0300, Kirill A. Shutemov wrote:
> Vlastimil noted[1] that pmd can be no longer valid after we drop
> mmap_sem. We need recheck it once mmap_sem taken again.
> 
> [1] http://lkml.kernel.org/r/12918dcd-a695-c6f4-e06f-69141c5f357f@suse.cz
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>  mm/huge_memory.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index d7ccc8558187..0efdad975659 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2437,6 +2437,9 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
>  			/* vma is no longer available, don't continue to swapin */
>  			if (hugepage_vma_revalidate(mm, address))
>  				return false;
> +			/* check if the pmd is still valid */
> +			if (mm_find_pmd(mm, address) != pmd)
> +				return false;
>  		}
Thanks for fixing this.

>  		if (ret & VM_FAULT_ERROR) {
>  			trace_mm_collapse_huge_page_swapin(mm, swapped_in, 0);
> @@ -2522,6 +2525,9 @@ static void collapse_huge_page(struct mm_struct *mm,
>  	result = hugepage_vma_revalidate(mm, address);
>  	if (result)
>  		goto out;
> +	/* check if the pmd is still valid */
> +	if (mm_find_pmd(mm, address) != pmd)
> +		goto out;
>  
However here, I don't know do we need to check pmd.
Because in collapse_huge_page; pmd is newly created,
after taking mmap_sem read:
{

	pmd_t *pmd, _pmd;
        pte_t *pte;
        ...
        down_read(&mm->mmap_sem);
        result = hugepage_vma_revalidate(mm, address);
        ...
        pmd = mm_find_pmd(mm, address);
        ...

Therefore it did not seem like a problem for me.

>  	anon_vma_lock_write(vma->anon_vma);
>  
> -- 
> 2.8.1
>