x86/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)

Change the gup code to replace ACCESS_ONCE with READ_ONCE.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
index 207d9aef662def24bfef094ff587f56f33afa595..d7547824e76369d6e14ed6ddd7ee39a55ef94a2e 100644 (file)
--- a/arch/x86/mm/gup.c
+++ b/arch/x86/mm/gup.c
@@ -15,7 +15,7 @@
 static inline pte_t gup_get_pte(pte_t *ptep)
 {
 #ifndef CONFIG_X86_PAE
-       return ACCESS_ONCE(*ptep);
+       return READ_ONCE(*ptep);
 #else
        /*
         * With get_user_pages_fast, we walk down the pagetables without taking