s390/spinlock: cleanup spinlock code

Improve the spinlock code in several aspects:
 - Have _raw_compare_and_swap return true if the operation has been
   successful instead of returning the old value.
 - Remove the "volatile" from arch_spinlock_t and arch_rwlock_t
 - Rename 'owner_cpu' to 'lock'
 - Add helper functions arch_spin_trylock_once / arch_spin_tryrelease_once

[ Martin Schwidefsky: patch breakdown and code beautification ]

Signed-off-by: Philipp Hachtmann <phacht@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/spinlock.h

@@ -14,15 +14,16 @@
 extern int spin_retry;
 
 static inline int
-_raw_compare_and_swap(volatile unsigned int *lock,
-		      unsigned int old, unsigned int new)
+_raw_compare_and_swap(unsigned int *lock, unsigned int old, unsigned int new)
 {
+	unsigned int old_expected = old;
+
 	asm volatile(
 		"	cs	%0,%3,%1"
 		: "=d" (old), "=Q" (*lock)
 		: "0" (old), "d" (new), "Q" (*lock)
 		: "cc", "memory" );
-	return old;
+	return old == old_expected;
 }
 
 /*
@@ -34,57 +35,66 @@ _raw_compare_and_swap(volatile unsigned int *lock,
  * (the type definitions are in asm/spinlock_types.h)
  */
 
-#define arch_spin_is_locked(x) ((x)->owner_cpu != 0)
-#define arch_spin_unlock_wait(lock) \
-	do { while (arch_spin_is_locked(lock)) \
-		 arch_spin_relax(lock); } while (0)
-
-extern void arch_spin_lock_wait(arch_spinlock_t *);
-extern void arch_spin_lock_wait_flags(arch_spinlock_t *, unsigned long flags);
-extern int arch_spin_trylock_retry(arch_spinlock_t *);
-extern void arch_spin_relax(arch_spinlock_t *lock);
+void arch_spin_lock_wait(arch_spinlock_t *);
+int arch_spin_trylock_retry(arch_spinlock_t *);
+void arch_spin_relax(arch_spinlock_t *);
+void arch_spin_lock_wait_flags(arch_spinlock_t *, unsigned long flags);
 
 static inline int arch_spin_value_unlocked(arch_spinlock_t lock)
 {
-	return lock.owner_cpu == 0;
+	return lock.lock == 0;
 }
 
-static inline void arch_spin_lock(arch_spinlock_t *lp)
+static inline int arch_spin_is_locked(arch_spinlock_t *lp)
+{
+	return ACCESS_ONCE(lp->lock) != 0;
+}
+
+static inline int arch_spin_trylock_once(arch_spinlock_t *lp)
 {
-	int old;
+	unsigned int new = ~smp_processor_id();
 
-	old = _raw_compare_and_swap(&lp->owner_cpu, 0, ~smp_processor_id());
-	if (likely(old == 0))
-		return;
-	arch_spin_lock_wait(lp);
+	return _raw_compare_and_swap(&lp->lock, 0, new);
 }
 
-static inline void arch_spin_lock_flags(arch_spinlock_t *lp,
-					 unsigned long flags)
+static inline int arch_spin_tryrelease_once(arch_spinlock_t *lp)
 {
-	int old;
+	unsigned int old = ~smp_processor_id();
 
-	old = _raw_compare_and_swap(&lp->owner_cpu, 0, ~smp_processor_id());
-	if (likely(old == 0))
-		return;
-	arch_spin_lock_wait_flags(lp, flags);
+	return _raw_compare_and_swap(&lp->lock, old, 0);
 }
 
-static inline int arch_spin_trylock(arch_spinlock_t *lp)
+static inline void arch_spin_lock(arch_spinlock_t *lp)
 {
-	int old;
+	if (unlikely(!arch_spin_trylock_once(lp)))
+		arch_spin_lock_wait(lp);
+}
 
-	old = _raw_compare_and_swap(&lp->owner_cpu, 0, ~smp_processor_id());
-	if (likely(old == 0))
-		return 1;
-	return arch_spin_trylock_retry(lp);
+static inline void arch_spin_lock_flags(arch_spinlock_t *lp,
+					unsigned long flags)
+{
+	if (unlikely(!arch_spin_trylock_once(lp)))
+		arch_spin_lock_wait_flags(lp, flags);
+}
+
+static inline int arch_spin_trylock(arch_spinlock_t *lp)
+{
+	if (unlikely(!arch_spin_trylock_once(lp)))
+		return arch_spin_trylock_retry(lp);
+	return 1;
 }
 
 static inline void arch_spin_unlock(arch_spinlock_t *lp)
 {
-	_raw_compare_and_swap(&lp->owner_cpu, lp->owner_cpu, 0);
+	arch_spin_tryrelease_once(lp);
 }
-		
+
+static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
+{
+	while (arch_spin_is_locked(lock))
+		arch_spin_relax(lock);
+}
+
 /*
  * Read-write spinlocks, allowing multiple readers
  * but only one writer.
@@ -119,7 +129,7 @@ static inline void arch_read_lock(arch_rwlock_t *rw)
 {
 	unsigned int old;
 	old = rw->lock & 0x7fffffffU;
-	if (_raw_compare_and_swap(&rw->lock, old, old + 1) != old)
+	if (!_raw_compare_and_swap(&rw->lock, old, old + 1))
 		_raw_read_lock_wait(rw);
 }
 
@@ -127,30 +137,28 @@ static inline void arch_read_lock_flags(arch_rwlock_t *rw, unsigned long flags)
 {
 	unsigned int old;
 	old = rw->lock & 0x7fffffffU;
-	if (_raw_compare_and_swap(&rw->lock, old, old + 1) != old)
+	if (!_raw_compare_and_swap(&rw->lock, old, old + 1))
 		_raw_read_lock_wait_flags(rw, flags);
 }
 
 static inline void arch_read_unlock(arch_rwlock_t *rw)
 {
-	unsigned int old, cmp;
+	unsigned int old;
 
-	old = rw->lock;
 	do {
-		cmp = old;
-		old = _raw_compare_and_swap(&rw->lock, old, old - 1);
-	} while (cmp != old);
+		old = ACCESS_ONCE(rw->lock);
+	} while (!_raw_compare_and_swap(&rw->lock, old, old - 1));
 }
 
 static inline void arch_write_lock(arch_rwlock_t *rw)
 {
-	if (unlikely(_raw_compare_and_swap(&rw->lock, 0, 0x80000000) != 0))
+	if (unlikely(!_raw_compare_and_swap(&rw->lock, 0, 0x80000000)))
 		_raw_write_lock_wait(rw);
 }
 
 static inline void arch_write_lock_flags(arch_rwlock_t *rw, unsigned long flags)
 {
-	if (unlikely(_raw_compare_and_swap(&rw->lock, 0, 0x80000000) != 0))
+	if (unlikely(!_raw_compare_and_swap(&rw->lock, 0, 0x80000000)))
 		_raw_write_lock_wait_flags(rw, flags);
 }
 
@@ -163,14 +171,14 @@ static inline int arch_read_trylock(arch_rwlock_t *rw)
 {
 	unsigned int old;
 	old = rw->lock & 0x7fffffffU;
-	if (likely(_raw_compare_and_swap(&rw->lock, old, old + 1) == old))
+	if (likely(_raw_compare_and_swap(&rw->lock, old, old + 1)))
 		return 1;
 	return _raw_read_trylock_retry(rw);
 }
 
 static inline int arch_write_trylock(arch_rwlock_t *rw)
 {
-	if (likely(_raw_compare_and_swap(&rw->lock, 0, 0x80000000) == 0))
+	if (likely(_raw_compare_and_swap(&rw->lock, 0, 0x80000000)))
 		return 1;
 	return _raw_write_trylock_retry(rw);
 }

arch/s390/include/asm/spinlock_types.h

@@ -6,13 +6,13 @@
 #endif
 
 typedef struct {
-	volatile unsigned int owner_cpu;
+	unsigned int lock;
 } __attribute__ ((aligned (4))) arch_spinlock_t;
 
-#define __ARCH_SPIN_LOCK_UNLOCKED	{ 0 }
+#define __ARCH_SPIN_LOCK_UNLOCKED { .lock = 0, }
 
 typedef struct {
-	volatile unsigned int lock;
+	unsigned int lock;
 } arch_rwlock_t;
 
 #define __ARCH_RW_LOCK_UNLOCKED		{ 0 }

arch/s390/lib/spinlock.c

@@ -31,22 +31,21 @@ void arch_spin_lock_wait(arch_spinlock_t *lp)
 	unsigned int owner;
 
 	while (1) {
-		owner = lp->owner_cpu;
+		owner = lp->lock;
 		if (!owner || smp_vcpu_scheduled(~owner)) {
 			for (count = spin_retry; count > 0; count--) {
 				if (arch_spin_is_locked(lp))
 					continue;
-				if (_raw_compare_and_swap(&lp->owner_cpu, 0,
-							  cpu) == 0)
+				if (_raw_compare_and_swap(&lp->lock, 0, cpu))
 					return;
 			}
 			if (MACHINE_IS_LPAR)
 				continue;
 		}
-		owner = lp->owner_cpu;
+		owner = lp->lock;
 		if (owner)
 			smp_yield_cpu(~owner);
-		if (_raw_compare_and_swap(&lp->owner_cpu, 0, cpu) == 0)
+		if (_raw_compare_and_swap(&lp->lock, 0, cpu))
 			return;
 	}
 }
@@ -60,57 +59,55 @@ void arch_spin_lock_wait_flags(arch_spinlock_t *lp, unsigned long flags)
 
 	local_irq_restore(flags);
 	while (1) {
-		owner = lp->owner_cpu;
+		owner = lp->lock;
 		if (!owner || smp_vcpu_scheduled(~owner)) {
 			for (count = spin_retry; count > 0; count--) {
 				if (arch_spin_is_locked(lp))
 					continue;
 				local_irq_disable();
-				if (_raw_compare_and_swap(&lp->owner_cpu, 0,
-							  cpu) == 0)
+				if (_raw_compare_and_swap(&lp->lock, 0, cpu))
 					return;
 				local_irq_restore(flags);
 			}
 			if (MACHINE_IS_LPAR)
 				continue;
 		}
-		owner = lp->owner_cpu;
+		owner = lp->lock;
 		if (owner)
 			smp_yield_cpu(~owner);
 		local_irq_disable();
-		if (_raw_compare_and_swap(&lp->owner_cpu, 0, cpu) == 0)
+		if (_raw_compare_and_swap(&lp->lock, 0, cpu))
 			return;
 		local_irq_restore(flags);
 	}
 }
 EXPORT_SYMBOL(arch_spin_lock_wait_flags);
 
+void arch_spin_relax(arch_spinlock_t *lp)
+{
+	unsigned int cpu = lp->lock;
+	if (cpu != 0) {
+		if (MACHINE_IS_VM || MACHINE_IS_KVM ||
+		    !smp_vcpu_scheduled(~cpu))
+			smp_yield_cpu(~cpu);
+	}
+}
+EXPORT_SYMBOL(arch_spin_relax);
+
 int arch_spin_trylock_retry(arch_spinlock_t *lp)
 {
-	unsigned int cpu = ~smp_processor_id();
 	int count;
 
 	for (count = spin_retry; count > 0; count--) {
 		if (arch_spin_is_locked(lp))
 			continue;
-		if (_raw_compare_and_swap(&lp->owner_cpu, 0, cpu) == 0)
+		if (arch_spin_trylock_once(lp))
 			return 1;
 	}
 	return 0;
 }
 EXPORT_SYMBOL(arch_spin_trylock_retry);
 
-void arch_spin_relax(arch_spinlock_t *lock)
-{
-	unsigned int cpu = lock->owner_cpu;
-	if (cpu != 0) {
-		if (MACHINE_IS_VM || MACHINE_IS_KVM ||
-		    !smp_vcpu_scheduled(~cpu))
-			smp_yield_cpu(~cpu);
-	}
-}
-EXPORT_SYMBOL(arch_spin_relax);
-
 void _raw_read_lock_wait(arch_rwlock_t *rw)
 {
 	unsigned int old;
@@ -124,7 +121,7 @@ void _raw_read_lock_wait(arch_rwlock_t *rw)
 		if (!arch_read_can_lock(rw))
 			continue;
 		old = rw->lock & 0x7fffffffU;
-		if (_raw_compare_and_swap(&rw->lock, old, old + 1) == old)
+		if (_raw_compare_and_swap(&rw->lock, old, old + 1))
 			return;
 	}
 }
@@ -145,7 +142,7 @@ void _raw_read_lock_wait_flags(arch_rwlock_t *rw, unsigned long flags)
 			continue;
 		old = rw->lock & 0x7fffffffU;
 		local_irq_disable();
-		if (_raw_compare_and_swap(&rw->lock, old, old + 1) == old)
+		if (_raw_compare_and_swap(&rw->lock, old, old + 1))
 			return;
 	}
 }
@@ -160,7 +157,7 @@ int _raw_read_trylock_retry(arch_rwlock_t *rw)
 		if (!arch_read_can_lock(rw))
 			continue;
 		old = rw->lock & 0x7fffffffU;
-		if (_raw_compare_and_swap(&rw->lock, old, old + 1) == old)
+		if (_raw_compare_and_swap(&rw->lock, old, old + 1))
 			return 1;
 	}
 	return 0;
@@ -178,7 +175,7 @@ void _raw_write_lock_wait(arch_rwlock_t *rw)
 		}
 		if (!arch_write_can_lock(rw))
 			continue;
-		if (_raw_compare_and_swap(&rw->lock, 0, 0x80000000) == 0)
+		if (_raw_compare_and_swap(&rw->lock, 0, 0x80000000))
 			return;
 	}
 }
@@ -197,7 +194,7 @@ void _raw_write_lock_wait_flags(arch_rwlock_t *rw, unsigned long flags)
 		if (!arch_write_can_lock(rw))
 			continue;
 		local_irq_disable();
-		if (_raw_compare_and_swap(&rw->lock, 0, 0x80000000) == 0)
+		if (_raw_compare_and_swap(&rw->lock, 0, 0x80000000))
 			return;
 	}
 }
@@ -210,7 +207,7 @@ int _raw_write_trylock_retry(arch_rwlock_t *rw)
 	while (count-- > 0) {
 		if (!arch_write_can_lock(rw))
 			continue;
-		if (_raw_compare_and_swap(&rw->lock, 0, 0x80000000) == 0)
+		if (_raw_compare_and_swap(&rw->lock, 0, 0x80000000))
 			return 1;
 	}
 	return 0;