mm/gup: Replace ACCESS_ONCE with READ_ONCE

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)

Fixup gup_pmd_range.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

diff --git a/mm/gup.c b/mm/gup.c
index a900759..bed30ef 100644 (file)
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -926,7 +926,7 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
 
        pmdp = pmd_offset(&pud, addr);
        do {
-               pmd_t pmd = ACCESS_ONCE(*pmdp);
+               pmd_t pmd = READ_ONCE(*pmdp);
 
                next = pmd_addr_end(addr, end);
                if (pmd_none(pmd) || pmd_trans_splitting(pmd))