ARM: 7854/1: lockref: add support for lockless lockrefs using cmpxchg64
Our spinlocks are only 32-bit (2x16-bit tickets) and, on processors
with 64-bit atomic instructions, cmpxchg64 makes use of the double-word
exclusive accessors.
This patch wires up the cmpxchg-based lockless lockref implementation
for ARM.
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/include/asm/spinlock.h b/arch/arm/include/asm/spinlock.h
index 4f2c280..ed6c229 100644
--- a/arch/arm/include/asm/spinlock.h
+++ b/arch/arm/include/asm/spinlock.h
@@ -127,10 +127,14 @@
dsb_sev();
}
+static inline int arch_spin_value_unlocked(arch_spinlock_t lock)
+{
+ return lock.tickets.owner == lock.tickets.next;
+}
+
static inline int arch_spin_is_locked(arch_spinlock_t *lock)
{
- struct __raw_tickets tickets = ACCESS_ONCE(lock->tickets);
- return tickets.owner != tickets.next;
+ return !arch_spin_value_unlocked(ACCESS_ONCE(*lock));
}
static inline int arch_spin_is_contended(arch_spinlock_t *lock)