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powerpc/thp: Use ACCESS_ONCE when loading pmdp 

We would get wrong results in compiler recomputed old_pmd. Avoid
that by using ACCESS_ONCE

CC: <stable@vger.kernel.org>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Aneesh Kumar K.V 2014-08-13 12:32:02 +05:30 committed by Benjamin Herrenschmidt
parent 969b7b208f
commit 7e467245bf
1 changed files with 3 additions and 1 deletions
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4
arch/powerpc/mm/hugepage-hash64.c
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@ -84,7 +84,9 @@ int __hash_page_thp(unsigned long ea, unsigned long access, unsigned long vsid,
* atomically mark the linux large page PMD busy and dirty
*/
do {
old_pmd = pmd_val(*pmdp);
pmd_t pmd = ACCESS_ONCE(*pmdp);
old_pmd = pmd_val(pmd);
/* If PMD busy, retry the access */
if (unlikely(old_pmd & _PAGE_BUSY))
return 0;