On Tue, Apr 23, 2013 at 02:53:44PM -0700, Greg Kroah-Hartman wrote:
> 3.4-stable review patch. If anyone has any objections, please let me know.
>
> ------------------
>
> From: Naoya Horiguchi <n-horigu...@ah.jp.nec.com>
>
> commit 9cc3a5bd40067b9a0fbd49199d0780463fc2140f upstream.
>
> With applying the previous patch "hugetlbfs: stop setting VM_DONTDUMP in
> initializing vma(VM_HUGETLB)" to reenable hugepage coredump, if a memory
> error happens on a hugepage and the affected processes try to access the
> error hugepage, we hit VM_BUG_ON(atomic_read(&page->_count) <= 0) in
> get_page().
Is this required? You didn't apply the previous patch referred to
above (commit a2fce9143057) to 3.4.y or 3.0.y since it claimed to fix
a regression in 3.7 (commit 314e51b9851b 'mm: kill vma flag VM_RESERVED
and mm->reserved_vm counter').
I'm not saying it *isn't* required, mind.
Ben.
> The reason for this bug is that coredump-related code doesn't recognise
> "hugepage hwpoison entry" with which a pmd entry is replaced when a memory
> error occurs on a hugepage.
>
> In other words, physical address information is stored in different bit
> layout between hugepage hwpoison entry and pmd entry, so
> follow_hugetlb_page() which is called in get_dump_page() returns a wrong
> page from a given address.
>
> The expected behavior is like this:
>
> absent is_swap_pte FOLL_DUMP Expected behavior
> -------------------------------------------------------------------
> true false false hugetlb_fault
> false true false hugetlb_fault
> false false false return page
> true false true skip page (to avoid allocation)
> false true true hugetlb_fault
> false false true return page
>
> With this patch, we can call hugetlb_fault() and take proper actions (we
> wait for migration entries, fail with VM_FAULT_HWPOISON_LARGE for
> hwpoisoned entries,) and as the result we can dump all hugepages except
> for hwpoisoned ones.
>
> Signed-off-by: Naoya Horiguchi <n-horigu...@ah.jp.nec.com>
> Cc: Rik van Riel <r...@redhat.com>
> Acked-by: Michal Hocko <mho...@suse.cz>
> Cc: HATAYAMA Daisuke <d.hatay...@jp.fujitsu.com>
> Acked-by: KOSAKI Motohiro <kosaki.motoh...@jp.fujitsu.com>
> Acked-by: David Rientjes <rient...@google.com>
> Signed-off-by: Andrew Morton <a...@linux-foundation.org>
> Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
> Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
>
> ---
> mm/hugetlb.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2906,7 +2906,17 @@ int follow_hugetlb_page(struct mm_struct
> break;
> }
>
> - if (absent ||
> + /*
> + * We need call hugetlb_fault for both hugepages under migration
> + * (in which case hugetlb_fault waits for the migration,) and
> + * hwpoisoned hugepages (in which case we need to prevent the
> + * caller from accessing to them.) In order to do this, we use
> + * here is_swap_pte instead of is_hugetlb_entry_migration and
> + * is_hugetlb_entry_hwpoisoned. This is because it simply covers
> + * both cases, and because we can't follow correct pages
> + * directly from any kind of swap entries.
> + */
> + if (absent || is_swap_pte(huge_ptep_get(pte)) ||
> ((flags & FOLL_WRITE) && !pte_write(huge_ptep_get(pte)))) {
> int ret;
>
--
Ben Hutchings
We get into the habit of living before acquiring the habit of thinking.
- Albert Camus
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