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SubjectRe: [PATCH] mm, hugetlb, soft_offline: save compound page order before page migration
Date
Hi Alexandru,

On Tue, Sep 12, 2017 at 10:43:06PM +0200, Alexandru Moise wrote:
> This fixes a bug in madvise() where if you'd try to soft offline a
> hugepage via madvise(), while walking the address range you'd end up,
> using the wrong page offset due to attempting to get the compound
> order of a former but presently not compound page, due to dissolving
> the huge page (since c3114a8).
>
> Signed-off-by: Alexandru Moise <00moses.alexander00@gmail.com>

There was a similar discussion in https://marc.info/?l=linux-kernel&m=150354919510631&w=2
over thp. As I stated there, if we give multi-page range into the parameters
[start, end), we expect that memory errors are injected to every single page
within the range.

So I start to feel that we should revert the following patch which introduced
the multi-page stepping.

commit 20cb6cab52a21b46e3c0dc7bd23f004f810fb421
Author: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Date: Mon Sep 30 13:45:21 2013 -0700

mm/hwpoison: fix traversal of hugetlbfs pages to avoid printk flood

In order to suppress the printk flood, we can use ratelimit mechanism, or
just s/pr_info/pr_debug/ might be ok.

Thanks,
Naoya Horiguchi

> ---
> mm/madvise.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 21261ff0466f..25bade36e9ca 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -625,18 +625,26 @@ static int madvise_inject_error(int behavior,
> {
> struct page *page;
> struct zone *zone;
> + unsigned int order;
>
> if (!capable(CAP_SYS_ADMIN))
> return -EPERM;
>
> - for (; start < end; start += PAGE_SIZE <<
> - compound_order(compound_head(page))) {
> +
> + for (; start < end; start += PAGE_SIZE << order) {
> int ret;
>
> ret = get_user_pages_fast(start, 1, 0, &page);
> if (ret != 1)
> return ret;
>
> + /*
> + * When soft offlining hugepages, after migrating the page
> + * we dissolve it, therefore in the second loop "page" will
> + * no longer be a compound page, and order will be 0.
> + */
> + order = compound_order(compound_head(page));
> +
> if (PageHWPoison(page)) {
> put_page(page);
> continue;
> --
> 2.14.1
>
> --
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