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| author | Christian Borntraeger <borntraeger@de.ibm.com> | 2014-12-07 21:41:33 +0100 |
|---|---|---|
| committer | Christian Borntraeger <borntraeger@de.ibm.com> | 2014-12-18 09:54:37 +0100 |
| commit | e37c698270633327245beb0fbd8699db8a4b65b4 (patch) | |
| tree | ed83173785e55c3f91467a19d8c4033e723a98e9 /mm/rmap.c | |
| parent | 230fa253df6352af12ad0a16128760b5cb3f92df (diff) | |
| download | lwn-e37c698270633327245beb0fbd8699db8a4b65b4.tar.gz lwn-e37c698270633327245beb0fbd8699db8a4b65b4.zip | |
mm: replace ACCESS_ONCE with READ_ONCE or barriers
ACCESS_ONCE does not work reliably on non-scalar types. For
example gcc 4.6 and 4.7 might remove the volatile tag for such
accesses during the SRA (scalar replacement of aggregates) step
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145)
Let's change the code to access the page table elements with
READ_ONCE that does implicit scalar accesses for the gup code.
mm_find_pmd is tricky, because m68k and sparc(32bit) define pmd_t
as array of longs. This code requires just that the pmd_present
and pmd_trans_huge check are done on the same value, so a barrier
is sufficent.
A similar case is in handle_pte_fault. On ppc44x the word size is
32 bit, but a pte is 64 bit. A barrier is ok as well.
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: linux-mm@kvack.org
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'mm/rmap.c')
| -rw-r--r-- | mm/rmap.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/mm/rmap.c b/mm/rmap.c index 19886fb2f13a..1e542744e131 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -581,7 +581,8 @@ pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address) * without holding anon_vma lock for write. So when looking for a * genuine pmde (in which to find pte), test present and !THP together. */ - pmde = ACCESS_ONCE(*pmd); + pmde = *pmd; + barrier(); if (!pmd_present(pmde) || pmd_trans_huge(pmde)) pmd = NULL; out: |