diff options
| author | Andrea Arcangeli <aarcange@redhat.com> | 2012-10-08 16:33:27 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-10-09 16:22:57 +0900 |
| commit | 027ef6c87853b0a9df53175063028edb4950d476 (patch) | |
| tree | ccd9f65107923898792c630d2246b66e2420465d | |
| parent | 00ea8990aadf754bbbb46ae85d4f2afba19508d8 (diff) | |
mm: thp: fix pmd_present for split_huge_page and PROT_NONE with THP
In many places !pmd_present has been converted to pmd_none. For pmds
that's equivalent and pmd_none is quicker so using pmd_none is better.
However (unless we delete pmd_present) we should provide an accurate
pmd_present too. This will avoid the risk of code thinking the pmd is non
present because it's under __split_huge_page_map, see the pmd_mknotpresent
there and the comment above it.
If the page has been mprotected as PROT_NONE, it would also lead to a
pmd_present false negative in the same way as the race with
split_huge_page.
Because the PSE bit stays on at all times (both during split_huge_page and
when the _PAGE_PROTNONE bit get set), we could only check for the PSE bit,
but checking the PROTNONE bit too is still good to remember pmd_present
must always keep PROT_NONE into account.
This explains a not reproducible BUG_ON that was seldom reported on the
lists.
The same issue is in pmd_large, it would go wrong with both PROT_NONE and
if it races with split_huge_page.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | arch/x86/include/asm/pgtable.h | 11 |
1 files changed, 8 insertions, 3 deletions
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h index fc9948465293..a1f780d45f76 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -146,8 +146,7 @@ static inline unsigned long pmd_pfn(pmd_t pmd) static inline int pmd_large(pmd_t pte) { - return (pmd_flags(pte) & (_PAGE_PSE | _PAGE_PRESENT)) == - (_PAGE_PSE | _PAGE_PRESENT); + return pmd_flags(pte) & _PAGE_PSE; } #ifdef CONFIG_TRANSPARENT_HUGEPAGE @@ -415,7 +414,13 @@ static inline int pte_hidden(pte_t pte) static inline int pmd_present(pmd_t pmd) { - return pmd_flags(pmd) & _PAGE_PRESENT; + /* + * Checking for _PAGE_PSE is needed too because + * split_huge_page will temporarily clear the present bit (but + * the _PAGE_PSE flag will remain set at all times while the + * _PAGE_PRESENT bit is clear). + */ + return pmd_flags(pmd) & (_PAGE_PRESENT | _PAGE_PROTNONE | _PAGE_PSE); } static inline int pmd_none(pmd_t pmd) |