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authorChristian Borntraeger <borntraeger@de.ibm.com>2014-11-24 12:53:46 +0300
committerChristian Borntraeger <borntraeger@de.ibm.com>2014-12-18 11:54:38 +0300
commit4f9d1382e6f80dcfa891b2c02d5a35c53be485f1 (patch)
treed4d95efc68ca6661661e08fe78b1ff3538baa5de
parente37c698270633327245beb0fbd8699db8a4b65b4 (diff)
downloadlinux-4f9d1382e6f80dcfa891b2c02d5a35c53be485f1.tar.xz
x86/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@de.ibm.com> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
-rw-r--r--arch/x86/include/asm/spinlock.h8
1 files changed, 4 insertions, 4 deletions
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 9295016485c9..12a69b406d40 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -92,7 +92,7 @@ static __always_inline void arch_spin_lock(arch_spinlock_t *lock)
unsigned count = SPIN_THRESHOLD;
do {
- if (ACCESS_ONCE(lock->tickets.head) == inc.tail)
+ if (READ_ONCE(lock->tickets.head) == inc.tail)
goto out;
cpu_relax();
} while (--count);
@@ -105,7 +105,7 @@ static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
{
arch_spinlock_t old, new;
- old.tickets = ACCESS_ONCE(lock->tickets);
+ old.tickets = READ_ONCE(lock->tickets);
if (old.tickets.head != (old.tickets.tail & ~TICKET_SLOWPATH_FLAG))
return 0;
@@ -162,14 +162,14 @@ static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
static inline int arch_spin_is_locked(arch_spinlock_t *lock)
{
- struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
+ struct __raw_tickets tmp = READ_ONCE(lock->tickets);
return tmp.tail != tmp.head;
}
static inline int arch_spin_is_contended(arch_spinlock_t *lock)
{
- struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
+ struct __raw_tickets tmp = READ_ONCE(lock->tickets);
return (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC;
}