Merge branch 'locking/urgent' into locking/core, before applying larger changes and to refresh the branch with fixes

Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/locking/mcs_spinlock.c

@@ -14,21 +14,47 @@
  * called from interrupt context and we have preemption disabled while
  * spinning.
  */
-static DEFINE_PER_CPU_SHARED_ALIGNED(struct optimistic_spin_queue, osq_node);
+static DEFINE_PER_CPU_SHARED_ALIGNED(struct optimistic_spin_node, osq_node);
+
+/*
+ * We use the value 0 to represent "no CPU", thus the encoded value
+ * will be the CPU number incremented by 1.
+ */
+static inline int encode_cpu(int cpu_nr)
+{
+	return cpu_nr + 1;
+}
+
+static inline struct optimistic_spin_node *decode_cpu(int encoded_cpu_val)
+{
+	int cpu_nr = encoded_cpu_val - 1;
+
+	return per_cpu_ptr(&osq_node, cpu_nr);
+}
 
 /*
  * Get a stable @node->next pointer, either for unlock() or unqueue() purposes.
  * Can return NULL in case we were the last queued and we updated @lock instead.
  */
-static inline struct optimistic_spin_queue *
-osq_wait_next(struct optimistic_spin_queue **lock,
-	      struct optimistic_spin_queue *node,
-	      struct optimistic_spin_queue *prev)
+static inline struct optimistic_spin_node *
+osq_wait_next(struct optimistic_spin_queue *lock,
+	      struct optimistic_spin_node *node,
+	      struct optimistic_spin_node *prev)
 {
-	struct optimistic_spin_queue *next = NULL;
+	struct optimistic_spin_node *next = NULL;
+	int curr = encode_cpu(smp_processor_id());
+	int old;
+
+	/*
+	 * If there is a prev node in queue, then the 'old' value will be
+	 * the prev node's CPU #, else it's set to OSQ_UNLOCKED_VAL since if
+	 * we're currently last in queue, then the queue will then become empty.
+	 */
+	old = prev ? prev->cpu : OSQ_UNLOCKED_VAL;
 
 	for (;;) {
-		if (*lock == node && cmpxchg(lock, node, prev) == node) {
+		if (atomic_read(&lock->tail) == curr &&
+		    atomic_cmpxchg(&lock->tail, curr, old) == curr) {
 			/*
 			 * We were the last queued, we moved @lock back. @prev
 			 * will now observe @lock and will complete its
@@ -59,18 +85,23 @@ osq_wait_next(struct optimistic_spin_queue **lock,
 	return next;
 }
 
-bool osq_lock(struct optimistic_spin_queue **lock)
+bool osq_lock(struct optimistic_spin_queue *lock)
 {
-	struct optimistic_spin_queue *node = this_cpu_ptr(&osq_node);
-	struct optimistic_spin_queue *prev, *next;
+	struct optimistic_spin_node *node = this_cpu_ptr(&osq_node);
+	struct optimistic_spin_node *prev, *next;
+	int curr = encode_cpu(smp_processor_id());
+	int old;
 
 	node->locked = 0;
 	node->next = NULL;
+	node->cpu = curr;
 
-	node->prev = prev = xchg(lock, node);
-	if (likely(prev == NULL))
+	old = atomic_xchg(&lock->tail, curr);
+	if (old == OSQ_UNLOCKED_VAL)
 		return true;
 
+	prev = decode_cpu(old);
+	node->prev = prev;
 	ACCESS_ONCE(prev->next) = node;
 
 	/*
@@ -149,20 +180,21 @@ unqueue:
 	return false;
 }
 
-void osq_unlock(struct optimistic_spin_queue **lock)
+void osq_unlock(struct optimistic_spin_queue *lock)
 {
-	struct optimistic_spin_queue *node = this_cpu_ptr(&osq_node);
-	struct optimistic_spin_queue *next;
+	struct optimistic_spin_node *node, *next;
+	int curr = encode_cpu(smp_processor_id());
 
 	/*
 	 * Fast path for the uncontended case.
 	 */
-	if (likely(cmpxchg(lock, node, NULL) == node))
+	if (likely(atomic_cmpxchg(&lock->tail, curr, OSQ_UNLOCKED_VAL) == curr))
 		return;
 
 	/*
 	 * Second most likely case.
 	 */
+	node = this_cpu_ptr(&osq_node);
 	next = xchg(&node->next, NULL);
 	if (next) {
 		ACCESS_ONCE(next->locked) = 1;

kernel/locking/mcs_spinlock.h

@@ -118,12 +118,13 @@ void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
  * mutex_lock()/rwsem_down_{read,write}() etc.
  */
 
-struct optimistic_spin_queue {
-	struct optimistic_spin_queue *next, *prev;
+struct optimistic_spin_node {
+	struct optimistic_spin_node *next, *prev;
 	int locked; /* 1 if lock acquired */
+	int cpu; /* encoded CPU # value */
 };
 
-extern bool osq_lock(struct optimistic_spin_queue **lock);
-extern void osq_unlock(struct optimistic_spin_queue **lock);
+extern bool osq_lock(struct optimistic_spin_queue *lock);
+extern void osq_unlock(struct optimistic_spin_queue *lock);
 
 #endif /* __LINUX_MCS_SPINLOCK_H */

kernel/locking/mutex.c

@@ -54,7 +54,7 @@ __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
 	INIT_LIST_HEAD(&lock->wait_list);
 	mutex_clear_owner(lock);
 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
-	lock->osq = NULL;
+	osq_lock_init(&lock->osq);
 #endif
 
 	debug_mutex_init(lock, name, key);

kernel/locking/rwsem-spinlock.c

@@ -26,7 +26,7 @@ int rwsem_is_locked(struct rw_semaphore *sem)
 	unsigned long flags;
 
 	if (raw_spin_trylock_irqsave(&sem->wait_lock, flags)) {
-		ret = (sem->activity != 0);
+		ret = (sem->count != 0);
 		raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
 	}
 	return ret;
@@ -46,7 +46,7 @@ void __init_rwsem(struct rw_semaphore *sem, const char *name,
 	debug_check_no_locks_freed((void *)sem, sizeof(*sem));
 	lockdep_init_map(&sem->dep_map, name, key, 0);
 #endif
-	sem->activity = 0;
+	sem->count = 0;
 	raw_spin_lock_init(&sem->wait_lock);
 	INIT_LIST_HEAD(&sem->wait_list);
 }
@@ -95,7 +95,7 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wakewrite)
 		waiter = list_entry(next, struct rwsem_waiter, list);
 	} while (waiter->type != RWSEM_WAITING_FOR_WRITE);
 
-	sem->activity += woken;
+	sem->count += woken;
 
  out:
 	return sem;
@@ -126,9 +126,9 @@ void __sched __down_read(struct rw_semaphore *sem)
 
 	raw_spin_lock_irqsave(&sem->wait_lock, flags);
 
-	if (sem->activity >= 0 && list_empty(&sem->wait_list)) {
+	if (sem->count >= 0 && list_empty(&sem->wait_list)) {
 		/* granted */
-		sem->activity++;
+		sem->count++;
 		raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
 		goto out;
 	}
@@ -170,9 +170,9 @@ int __down_read_trylock(struct rw_semaphore *sem)
 
 	raw_spin_lock_irqsave(&sem->wait_lock, flags);
 
-	if (sem->activity >= 0 && list_empty(&sem->wait_list)) {
+	if (sem->count >= 0 && list_empty(&sem->wait_list)) {
 		/* granted */
-		sem->activity++;
+		sem->count++;
 		ret = 1;
 	}
 
@@ -206,7 +206,7 @@ void __sched __down_write_nested(struct rw_semaphore *sem, int subclass)
 		 * itself into sleep and waiting for system woke it or someone
 		 * else in the head of the wait list up.
 		 */
-		if (sem->activity == 0)
+		if (sem->count == 0)
 			break;
 		set_task_state(tsk, TASK_UNINTERRUPTIBLE);
 		raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
@@ -214,7 +214,7 @@ void __sched __down_write_nested(struct rw_semaphore *sem, int subclass)
 		raw_spin_lock_irqsave(&sem->wait_lock, flags);
 	}
 	/* got the lock */
-	sem->activity = -1;
+	sem->count = -1;
 	list_del(&waiter.list);
 
 	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
@@ -235,9 +235,9 @@ int __down_write_trylock(struct rw_semaphore *sem)
 
 	raw_spin_lock_irqsave(&sem->wait_lock, flags);
 
-	if (sem->activity == 0) {
+	if (sem->count == 0) {
 		/* got the lock */
-		sem->activity = -1;
+		sem->count = -1;
 		ret = 1;
 	}
 
@@ -255,7 +255,7 @@ void __up_read(struct rw_semaphore *sem)
 
 	raw_spin_lock_irqsave(&sem->wait_lock, flags);
 
-	if (--sem->activity == 0 && !list_empty(&sem->wait_list))
+	if (--sem->count == 0 && !list_empty(&sem->wait_list))
 		sem = __rwsem_wake_one_writer(sem);
 
 	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
@@ -270,7 +270,7 @@ void __up_write(struct rw_semaphore *sem)
 
 	raw_spin_lock_irqsave(&sem->wait_lock, flags);
 
-	sem->activity = 0;
+	sem->count = 0;
 	if (!list_empty(&sem->wait_list))
 		sem = __rwsem_do_wake(sem, 1);
 
@@ -287,7 +287,7 @@ void __downgrade_write(struct rw_semaphore *sem)
 
 	raw_spin_lock_irqsave(&sem->wait_lock, flags);
 
-	sem->activity = 1;
+	sem->count = 1;
 	if (!list_empty(&sem->wait_list))
 		sem = __rwsem_do_wake(sem, 0);
 

kernel/locking/rwsem-xadd.c

@@ -82,9 +82,9 @@ void __init_rwsem(struct rw_semaphore *sem, const char *name,
 	sem->count = RWSEM_UNLOCKED_VALUE;
 	raw_spin_lock_init(&sem->wait_lock);
 	INIT_LIST_HEAD(&sem->wait_list);
-#ifdef CONFIG_SMP
+#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 	sem->owner = NULL;
-	sem->osq = NULL;
+	osq_lock_init(&sem->osq);
 #endif
 }
 
@@ -262,7 +262,7 @@ static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem)
 	return false;
 }
 
-#ifdef CONFIG_SMP
+#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 /*
  * Try to acquire write lock before the writer has been put on wait queue.
  */
@@ -285,10 +285,10 @@ static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
 static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
 {
 	struct task_struct *owner;
-	bool on_cpu = true;
+	bool on_cpu = false;
 
 	if (need_resched())
-		return 0;
+		return false;
 
 	rcu_read_lock();
 	owner = ACCESS_ONCE(sem->owner);
@@ -297,9 +297,9 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
 	rcu_read_unlock();
 
 	/*
-	 * If sem->owner is not set, the rwsem owner may have
-	 * just acquired it and not set the owner yet or the rwsem
-	 * has been released.
+	 * If sem->owner is not set, yet we have just recently entered the
+	 * slowpath, then there is a possibility reader(s) may have the lock.
+	 * To be safe, avoid spinning in these situations.
 	 */
 	return on_cpu;
 }

kernel/locking/rwsem.c

@@ -12,7 +12,7 @@
 
 #include <linux/atomic.h>
 
-#if defined(CONFIG_SMP) && defined(CONFIG_RWSEM_XCHGADD_ALGORITHM)
+#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 static inline void rwsem_set_owner(struct rw_semaphore *sem)
 {
 	sem->owner = current;