Patch "hugetlbfs: add swap entry check in follow_hugetlb_page()" has been added to the 3.8-stable tree

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This is a note to let you know that I've just added the patch titled

    hugetlbfs: add swap entry check in follow_hugetlb_page()

to the 3.8-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     hugetlbfs-add-swap-entry-check-in-follow_hugetlb_page.patch
and it can be found in the queue-3.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 9cc3a5bd40067b9a0fbd49199d0780463fc2140f Mon Sep 17 00:00:00 2001
From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Date: Wed, 17 Apr 2013 15:58:30 -0700
Subject: hugetlbfs: add swap entry check in follow_hugetlb_page()

From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>

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().

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-horiguchi@xxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
Cc: HATAYAMA Daisuke <d.hatayama@xxxxxxxxxxxxxx>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 mm/hugetlb.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2965,7 +2965,17 @@ 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;
 


Patches currently in stable-queue which might be from n-horiguchi@xxxxxxxxxxxxx are

queue-3.8/fs-binfmt_elf.c-fix-hugetlb-memory-check-in-vma_dump_size.patch
queue-3.8/hugetlbfs-add-swap-entry-check-in-follow_hugetlb_page.patch
queue-3.8/hugetlbfs-stop-setting-vm_dontdump-in-initializing-vma-vm_hugetlb.patch
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