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authorChristian Borntraeger2014-12-07 21:41:33 +0100
committerChristian Borntraeger2014-12-18 09:54:37 +0100
commite37c698270633327245beb0fbd8699db8a4b65b4 (patch)
treeed83173785e55c3f91467a19d8c4033e723a98e9 /mm/rmap.c
parent230fa253df6352af12ad0a16128760b5cb3f92df (diff)
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.c3
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: