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>

3 files changed, 82 insertions, 77 deletions

diff --git a/arch/s390/include/asm/spinlock.h b/arch/s390/include/asm/spinlock.h
index 83e5d216105e..b60212a02d08 100644
--- a/arch/s390/include/asm/spinlock.h
+++ b/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);
 }
diff --git a/arch/s390/include/asm/spinlock_types.h b/arch/s390/include/asm/spinlock_types.h
index 9c76656a0af0..b2cd6ff7c2c5 100644
--- a/arch/s390/include/asm/spinlock_types.h
+++ b/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 }
diff --git a/arch/s390/lib/spinlock.c b/arch/s390/lib/spinlock.c
index f709983f41f8..4a3b33b2dbb9 100644
--- a/arch/s390/lib/spinlock.c
+++ b/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;