linux-kernel - [PATCHv2 05/10] x86: Replace ACCESS_ONCE in gup with READ

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Message-Id: <1416919117-50652-6-git-send-email-borntraeger@de.ibm.com>
Date:	Tue, 25 Nov 2014 13:38:32 +0100
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	"linux-arch@...r.kernel.org, linux-mips@...ux-mips.org, linux-x86_64@...r.kernel.org, linux-s390"@vger.kernel.org,
	Paolo Bonzini <pbonzini@...hat.com>,
	paulmck@...ux.vnet.ibm.com, mingo@...nel.org,
	torvalds@...ux-foundation.org,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	David Howells <dhowells@...hat.com>,
	Russell King <linux@....linux.org.uk>,
	Christian Borntraeger <borntraeger@...ibm.com>
Subject: [PATCHv2 05/10] x86: Replace ACCESS_ONCE in gup 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@...ibm.com>
---
 arch/x86/mm/gup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
index 207d9aef..d754782 100644
--- 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
-- 
1.9.3

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