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mm/hugetlb: pmd_huge() returns true for non-present hugepage

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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@ah.jp.nec.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Steve Capper <steve.capper@linaro.org>
Cc: <stable@vger.kernel.org>	[2.6.36+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Naoya Horiguchi 2015-02-11 15:25:19 -08:00 committed by Linus Torvalds
parent 61f77eda9b
commit cbef8478be
3 changed files with 10 additions and 2 deletions
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2
arch/x86/mm/gup.c
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@ -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)) if (pmd_none(pmd) || pmd_trans_splitting(pmd))
return 0; 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 * NUMA hinting faults need to be handled in the GUP
* slowpath for accounting purposes and so that they * slowpath for accounting purposes and so that they

8
arch/x86/mm/hugetlbpage.c
View File

@ -54,9 +54,15 @@ int pud_huge(pud_t pud)
#else #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) 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) int pud_huge(pud_t pud)

2
mm/hugetlb.c
View File

@ -3679,6 +3679,8 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address,
{ {
struct page *page; struct page *page;
if (!pmd_present(*pmd))
return NULL;
page = pte_page(*(pte_t *)pmd); page = pte_page(*(pte_t *)pmd);
if (page) if (page)
page += ((address & ~PMD_MASK) >> PAGE_SHIFT); page += ((address & ~PMD_MASK) >> PAGE_SHIFT);