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 use a barrier instead of ACCESS_ONCE to avoid that issue. Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> --- arch/x86/mm/gup.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c index 207d9aef..35991f6 100644 --- a/arch/x86/mm/gup.c +++ b/arch/x86/mm/gup.c @@ -14,8 +14,12 @@ static inline pte_t gup_get_pte(pte_t *ptep) { + pte_t pte; + #ifndef CONFIG_X86_PAE - return ACCESS_ONCE(*ptep); + pte = *ptep; + barrier(); + return pte; #else /* * With get_user_pages_fast, we walk down the pagetables without taking @@ -49,7 +53,6 @@ static inline pte_t gup_get_pte(pte_t *ptep) * very careful -- it does not atomically load the pte or anything that * is likely to be useful for you. */ - pte_t pte; retry: pte.pte_low = ptep->pte_low; -- 1.9.3
