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-rw-r--r--kernel/locking/mcs_spinlock.c64
-rw-r--r--kernel/locking/mcs_spinlock.h9
-rw-r--r--kernel/locking/mutex.c2
-rw-r--r--kernel/locking/rwsem-spinlock.c28
-rw-r--r--kernel/locking/rwsem-xadd.c16
-rw-r--r--kernel/locking/rwsem.c2
6 files changed, 77 insertions, 44 deletions
diff --git a/kernel/locking/mcs_spinlock.c b/kernel/locking/mcs_spinlock.c
index 838dc9e00669..be9ee1559fca 100644
--- a/kernel/locking/mcs_spinlock.c
+++ b/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;
diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h
index a2dbac4aca6b..74356dc0ce29 100644
--- a/kernel/locking/mcs_spinlock.h
+++ b/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 */
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index bc73d33c6760..acca2c1a3c5e 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -60,7 +60,7 @@ __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);
diff --git a/kernel/locking/rwsem-spinlock.c b/kernel/locking/rwsem-spinlock.c
index 9be8a9144978..2c93571162cb 100644
--- a/kernel/locking/rwsem-spinlock.c
+++ b/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);
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index dacc32142fcc..a2391ac135c8 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/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;
}
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 42f806de49d4..e2d3bc7f03b4 100644
--- a/kernel/locking/rwsem.c
+++ b/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;
generated by cgit v1.2.3 (git 2.25.1) at 2024-11-12 13:17:47 +0000