linux-kernel - [PATCH 2/8] ppc/hugetlbfs: Replace ACCESS_ONCE with READ

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Date:	Thu, 15 Jan 2015 09:58:28 +0100
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-arch@...r.kernel.org, kvm@...r.kernel.org,
	kvm-ppc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	x86@...nel.org, xen-devel@...ts.xenproject.org, linux-mm@...ck.org,
	Christian Borntraeger <borntraeger@...ibm.com>
Subject: [PATCH 2/8] ppc/hugetlbfs: 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 ppc/hugetlbfs code to replace ACCESS_ONCE with READ_ONCE.

Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
---
 arch/powerpc/mm/hugetlbpage.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index 5ff4e07..620d0ec 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -978,7 +978,7 @@ pte_t *find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea, unsigned *shift
 		 */
 		pdshift = PUD_SHIFT;
 		pudp = pud_offset(&pgd, ea);
-		pud  = ACCESS_ONCE(*pudp);
+		pud  = READ_ONCE(*pudp);
 
 		if (pud_none(pud))
 			return NULL;
@@ -990,7 +990,7 @@ pte_t *find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea, unsigned *shift
 		else {
 			pdshift = PMD_SHIFT;
 			pmdp = pmd_offset(&pud, ea);
-			pmd  = ACCESS_ONCE(*pmdp);
+			pmd  = READ_ONCE(*pmdp);
 			/*
 			 * A hugepage collapse is captured by pmd_none, because
 			 * it mark the pmd none and do a hpte invalidate.
-- 
1.9.3

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