On Tue, 27 Nov 2012 16:05:31 -0500
Naoya Horiguchi <n-horigu...@ah.jp.nec.com> wrote:
> When we try to soft-offline a thp tail page, put_page() is called on the
> tail page unthinkingly and VM_BUG_ON is triggered in put_compound_page().
> This patch splits thp before going into the main body of soft-offlining.
>
> The interface of soft-offlining is open for userspace, so this bug can
> lead to DoS attack and should be fixed immedately.
>
> Signed-off-by: Naoya Horiguchi <n-horigu...@ah.jp.nec.com>
> Cc: sta...@vger.kernel.org
> ---
> mm/memory-failure.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git v3.7-rc7.orig/mm/memory-failure.c v3.7-rc7/mm/memory-failure.c
> index 8fe3640..e48e235 100644
> --- v3.7-rc7.orig/mm/memory-failure.c
> +++ v3.7-rc7/mm/memory-failure.c
> @@ -1548,9 +1548,17 @@ int soft_offline_page(struct page *page, int flags)
> {
> int ret;
> unsigned long pfn = page_to_pfn(page);
> + struct page *hpage = compound_trans_head(page);
>
> if (PageHuge(page))
> return soft_offline_huge_page(page, flags);
> + if (PageTransHuge(hpage)) {
> + if (PageAnon(hpage) && unlikely(split_huge_page(hpage))) {
> + pr_info("soft offline: %#lx: failed to split THP\n",
> + pfn);
> + return -EBUSY;
> + }
> + }
We can use PageTransCompound() here, as we know it isn't a hugetlbfs
page. This will then permit the PageAnon() test to be omitted, methinks?
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