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x86/spinlock: Replace ACCESS_ONCE with READ_ONCE

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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>
This commit is contained in:
Christian Borntraeger 2014-11-24 10:53:46 +01:00
parent e37c698270
commit 4f9d1382e6
1 changed files with 4 additions and 4 deletions
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8
arch/x86/include/asm/spinlock.h
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@ -92,7 +92,7 @@ static __always_inline void arch_spin_lock(arch_spinlock_t *lock)
unsigned count = SPIN_THRESHOLD; unsigned count = SPIN_THRESHOLD;
do { do {
if (ACCESS_ONCE(lock->tickets.head) == inc.tail) if (READ_ONCE(lock->tickets.head) == inc.tail)
goto out; goto out;
cpu_relax(); cpu_relax();
} while (--count); } while (--count);
@ -105,7 +105,7 @@ static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
{ {
arch_spinlock_t old, new; 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)) if (old.tickets.head != (old.tickets.tail & ~TICKET_SLOWPATH_FLAG))
return 0; 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) 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; return tmp.tail != tmp.head;
} }
static inline int arch_spin_is_contended(arch_spinlock_t *lock) 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; return (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC;
} }