linux-kernel - Re: [PATCH 2/2] mm: hugetlbfs: Close race during teardown of hugetlbfs shared page tables

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]

Date:	Fri, 27 Jul 2012 13:24:45 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Larry Woodman <lwoodman@...hat.com>,
	Ken Chen <kenchen@...gle.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] mm: hugetlbfs: Close race during teardown of
 hugetlbfs shared page tables

Just a nit

On Fri 27-07-12 11:46:05, Mel Gorman wrote:
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index fd1d530..8c6e5a5 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2429,6 +2429,25 @@ again:
>  	tlb_end_vma(tlb, vma);
>  }
>

I would welcome a comment here. Something like:
/*
 * Called when the VMA is on the way out and page tables will be freed
 * by free_pagetables.
 * i_mmap_mutex has to be held when calling this function
 */

> +void __unmap_hugepage_range_final(struct mmu_gather *tlb,
> +			  struct vm_area_struct *vma, unsigned long start,
> +			  unsigned long end, struct page *ref_page)
> +{
> +	__unmap_hugepage_range(tlb, vma, start, end, ref_page);
> +
> +	/*
> +	 * Clear this flag so that x86's huge_pmd_share page_table_shareable
> +	 * test will fail on a vma being torn down, and not grab a page table
> +	 * on its way out.  We're lucky that the flag has such an appropriate
> +	 * name, and can in fact be safely cleared here. We could clear it
> +	 * before the __unmap_hugepage_range above, but all that's necessary
> +	 * is to clear it before releasing the i_mmap_mutex. This works
> +	 * because in the context this is called, the VMA is about to be
> +	 * destroyed and the i_mmap_mutex is held.
> +	 */
> +	vma->vm_flags &= ~VM_MAYSHARE;
> +}
> +

-- 
Michal Hocko
SUSE Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/