The patch below does not apply to the 3.10-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From cbef8478bee55775ac312a574aad48af7bb9cf9f Mon Sep 17 00:00:00 2001
From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Date: Wed, 11 Feb 2015 15:25:19 -0800
Subject: [PATCH] mm/hugetlb: pmd_huge() returns true for non-present hugepage
Migrating hugepages and hwpoisoned hugepages are considered as non-present
hugepages, and they are referenced via migration entries and hwpoison
entries in their page table slots.
This behavior causes race condition because pmd_huge() doesn't tell
non-huge pages from migrating/hwpoisoned hugepages. follow_page_mask() is
one example where the kernel would call follow_page_pte() for such
hugepage while this function is supposed to handle only normal pages.
To avoid this, this patch makes pmd_huge() return true when pmd_none() is
true *and* pmd_present() is false. We don't have to worry about mixing up
non-present pmd entry with normal pmd (pointing to leaf level pte entry)
because pmd_present() is true in normal pmd.
The same race condition could happen in (x86-specific) gup_pmd_range(),
where this patch simply adds pmd_present() check instead of pmd_huge().
This is because gup_pmd_range() is fast path. If we have non-present
hugepage in this function, we will go into gup_huge_pmd(), then return 0
at flag mask check, and finally fall back to the slow path.
Fixes: 290408d4a2 ("hugetlb: hugepage migration core")
Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: James Hogan <james.hogan@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Mel Gorman <mel@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Luiz Capitulino <lcapitulino@xxxxxxxxxx>
Cc: Nishanth Aravamudan <nacc@xxxxxxxxxxxxxxxxxx>
Cc: Lee Schermerhorn <lee.schermerhorn@xxxxxx>
Cc: Steve Capper <steve.capper@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [2.6.36+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
index d7547824e763..224b14235e96 100644
--- a/arch/x86/mm/gup.c
+++ b/arch/x86/mm/gup.c
@@ -172,7 +172,7 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
*/
if (pmd_none(pmd) || pmd_trans_splitting(pmd))
return 0;
- if (unlikely(pmd_large(pmd))) {
+ if (unlikely(pmd_large(pmd) || !pmd_present(pmd))) {
/*
* NUMA hinting faults need to be handled in the GUP
* slowpath for accounting purposes and so that they
diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
index f48423f10141..42982b26e32b 100644
--- a/arch/x86/mm/hugetlbpage.c
+++ b/arch/x86/mm/hugetlbpage.c
@@ -54,9 +54,15 @@ int pud_huge(pud_t pud)
#else
+/*
+ * pmd_huge() returns 1 if @pmd is hugetlb related entry, that is normal
+ * hugetlb entry or non-present (migration or hwpoisoned) hugetlb entry.
+ * Otherwise, returns 0.
+ */
int pmd_huge(pmd_t pmd)
{
- return !!(pmd_val(pmd) & _PAGE_PSE);
+ return !pmd_none(pmd) &&
+ (pmd_val(pmd) & (_PAGE_PRESENT|_PAGE_PSE)) != _PAGE_PRESENT;
}
int pud_huge(pud_t pud)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index f533d336e569..d96b8bfa748f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3679,6 +3679,8 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address,
{
struct page *page;
+ if (!pmd_present(*pmd))
+ return NULL;
page = pte_page(*(pte_t *)pmd);
if (page)
page += ((address & ~PMD_MASK) >> PAGE_SHIFT);
--
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