linux-kernel - [PATCH 7/8] arm/spinlock: Replace ACCESS_ONCE with READ

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Message-Id: <1418306712-17245-8-git-send-email-borntraeger@de.ibm.com>
Date:	Thu, 11 Dec 2014 15:05:10 +0100
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-arch@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	torvalds@...ux-foundation.org, George Spelvin <linux@...izon.com>,
	Christian Borntraeger <borntraeger@...ibm.com>
Subject: [PATCH 7/8] arm/spinlock: 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 spinlock code to replace ACCESS_ONCE with READ_ONCE.

Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 arch/arm/include/asm/spinlock.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/include/asm/spinlock.h b/arch/arm/include/asm/spinlock.h
index ac4bfae..0fa4184 100644
--- a/arch/arm/include/asm/spinlock.h
+++ b/arch/arm/include/asm/spinlock.h
@@ -120,12 +120,12 @@ static inline int arch_spin_value_unlocked(arch_spinlock_t lock)
 
 static inline int arch_spin_is_locked(arch_spinlock_t *lock)
 {
-	return !arch_spin_value_unlocked(ACCESS_ONCE(*lock));
+	return !arch_spin_value_unlocked(READ_ONCE(*lock));
 }
 
 static inline int arch_spin_is_contended(arch_spinlock_t *lock)
 {
-	struct __raw_tickets tickets = ACCESS_ONCE(lock->tickets);
+	struct __raw_tickets tickets = READ_ONCE(lock->tickets);
 	return (tickets.next - tickets.owner) > 1;
 }
 #define arch_spin_is_contended	arch_spin_is_contended
-- 
1.9.3

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