From ed428bfc3caaa4b1e6cd15ea12c90c30291903f0 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Thu, 31 Oct 2013 18:19:28 +0100 Subject: locking: Move the rwsem code to kernel/locking/ Notably: changed lib/rwsem* targets from lib- to obj-, no idea about the ramifications of that. Suggested-by: Ingo Molnar Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/n/tip-g0kynfh5feriwc6p3h6kpbw6@git.kernel.org Signed-off-by: Ingo Molnar diff --git a/kernel/Makefile b/kernel/Makefile index 9c2ad18..1aef002 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -8,7 +8,7 @@ obj-y = fork.o exec_domain.o panic.o \ signal.o sys.o kmod.o workqueue.o pid.o task_work.o \ extable.o params.o posix-timers.o \ kthread.o sys_ni.o posix-cpu-timers.o \ - hrtimer.o rwsem.o nsproxy.o \ + hrtimer.o nsproxy.o \ notifier.o ksysfs.o cred.o reboot.o \ async.o range.o groups.o lglock.o smpboot.o diff --git a/kernel/locking/Makefile b/kernel/locking/Makefile index 59f66de..b0e0d73 100644 --- a/kernel/locking/Makefile +++ b/kernel/locking/Makefile @@ -1,5 +1,5 @@ -obj-y += mutex.o semaphore.o +obj-y += mutex.o semaphore.o rwsem.o ifdef CONFIG_FUNCTION_TRACER CFLAGS_REMOVE_lockdep.o = -pg @@ -20,3 +20,5 @@ obj-$(CONFIG_DEBUG_RT_MUTEXES) += rtmutex-debug.o obj-$(CONFIG_RT_MUTEX_TESTER) += rtmutex-tester.o obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock.o obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock_debug.o +obj-$(CONFIG_RWSEM_GENERIC_SPINLOCK) += rwsem-spinlock.o +obj-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem-xadd.o \ No newline at end of file diff --git a/kernel/locking/rwsem-spinlock.c b/kernel/locking/rwsem-spinlock.c new file mode 100644 index 0000000..9be8a91 --- /dev/null +++ b/kernel/locking/rwsem-spinlock.c @@ -0,0 +1,296 @@ +/* rwsem-spinlock.c: R/W semaphores: contention handling functions for + * generic spinlock implementation + * + * Copyright (c) 2001 David Howells (dhowells@redhat.com). + * - Derived partially from idea by Andrea Arcangeli + * - Derived also from comments by Linus + */ +#include +#include +#include + +enum rwsem_waiter_type { + RWSEM_WAITING_FOR_WRITE, + RWSEM_WAITING_FOR_READ +}; + +struct rwsem_waiter { + struct list_head list; + struct task_struct *task; + enum rwsem_waiter_type type; +}; + +int rwsem_is_locked(struct rw_semaphore *sem) +{ + int ret = 1; + unsigned long flags; + + if (raw_spin_trylock_irqsave(&sem->wait_lock, flags)) { + ret = (sem->activity != 0); + raw_spin_unlock_irqrestore(&sem->wait_lock, flags); + } + return ret; +} +EXPORT_SYMBOL(rwsem_is_locked); + +/* + * initialise the semaphore + */ +void __init_rwsem(struct rw_semaphore *sem, const char *name, + struct lock_class_key *key) +{ +#ifdef CONFIG_DEBUG_LOCK_ALLOC + /* + * Make sure we are not reinitializing a held semaphore: + */ + debug_check_no_locks_freed((void *)sem, sizeof(*sem)); + lockdep_init_map(&sem->dep_map, name, key, 0); +#endif + sem->activity = 0; + raw_spin_lock_init(&sem->wait_lock); + INIT_LIST_HEAD(&sem->wait_list); +} +EXPORT_SYMBOL(__init_rwsem); + +/* + * handle the lock release when processes blocked on it that can now run + * - if we come here, then: + * - the 'active count' _reached_ zero + * - the 'waiting count' is non-zero + * - the spinlock must be held by the caller + * - woken process blocks are discarded from the list after having task zeroed + * - writers are only woken if wakewrite is non-zero + */ +static inline struct rw_semaphore * +__rwsem_do_wake(struct rw_semaphore *sem, int wakewrite) +{ + struct rwsem_waiter *waiter; + struct task_struct *tsk; + int woken; + + waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); + + if (waiter->type == RWSEM_WAITING_FOR_WRITE) { + if (wakewrite) + /* Wake up a writer. Note that we do not grant it the + * lock - it will have to acquire it when it runs. */ + wake_up_process(waiter->task); + goto out; + } + + /* grant an infinite number of read locks to the front of the queue */ + woken = 0; + do { + struct list_head *next = waiter->list.next; + + list_del(&waiter->list); + tsk = waiter->task; + smp_mb(); + waiter->task = NULL; + wake_up_process(tsk); + put_task_struct(tsk); + woken++; + if (next == &sem->wait_list) + break; + waiter = list_entry(next, struct rwsem_waiter, list); + } while (waiter->type != RWSEM_WAITING_FOR_WRITE); + + sem->activity += woken; + + out: + return sem; +} + +/* + * wake a single writer + */ +static inline struct rw_semaphore * +__rwsem_wake_one_writer(struct rw_semaphore *sem) +{ + struct rwsem_waiter *waiter; + + waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); + wake_up_process(waiter->task); + + return sem; +} + +/* + * get a read lock on the semaphore + */ +void __sched __down_read(struct rw_semaphore *sem) +{ + struct rwsem_waiter waiter; + struct task_struct *tsk; + unsigned long flags; + + raw_spin_lock_irqsave(&sem->wait_lock, flags); + + if (sem->activity >= 0 && list_empty(&sem->wait_list)) { + /* granted */ + sem->activity++; + raw_spin_unlock_irqrestore(&sem->wait_lock, flags); + goto out; + } + + tsk = current; + set_task_state(tsk, TASK_UNINTERRUPTIBLE); + + /* set up my own style of waitqueue */ + waiter.task = tsk; + waiter.type = RWSEM_WAITING_FOR_READ; + get_task_struct(tsk); + + list_add_tail(&waiter.list, &sem->wait_list); + + /* we don't need to touch the semaphore struct anymore */ + raw_spin_unlock_irqrestore(&sem->wait_lock, flags); + + /* wait to be given the lock */ + for (;;) { + if (!waiter.task) + break; + schedule(); + set_task_state(tsk, TASK_UNINTERRUPTIBLE); + } + + tsk->state = TASK_RUNNING; + out: + ; +} + +/* + * trylock for reading -- returns 1 if successful, 0 if contention + */ +int __down_read_trylock(struct rw_semaphore *sem) +{ + unsigned long flags; + int ret = 0; + + + raw_spin_lock_irqsave(&sem->wait_lock, flags); + + if (sem->activity >= 0 && list_empty(&sem->wait_list)) { + /* granted */ + sem->activity++; + ret = 1; + } + + raw_spin_unlock_irqrestore(&sem->wait_lock, flags); + + return ret; +} + +/* + * get a write lock on the semaphore + */ +void __sched __down_write_nested(struct rw_semaphore *sem, int subclass) +{ + struct rwsem_waiter waiter; + struct task_struct *tsk; + unsigned long flags; + + raw_spin_lock_irqsave(&sem->wait_lock, flags); + + /* set up my own style of waitqueue */ + tsk = current; + waiter.task = tsk; + waiter.type = RWSEM_WAITING_FOR_WRITE; + list_add_tail(&waiter.list, &sem->wait_list); + + /* wait for someone to release the lock */ + for (;;) { + /* + * That is the key to support write lock stealing: allows the + * task already on CPU to get the lock soon rather than put + * itself into sleep and waiting for system woke it or someone + * else in the head of the wait list up. + */ + if (sem->activity == 0) + break; + set_task_state(tsk, TASK_UNINTERRUPTIBLE); + raw_spin_unlock_irqrestore(&sem->wait_lock, flags); + schedule(); + raw_spin_lock_irqsave(&sem->wait_lock, flags); + } + /* got the lock */ + sem->activity = -1; + list_del(&waiter.list); + + raw_spin_unlock_irqrestore(&sem->wait_lock, flags); +} + +void __sched __down_write(struct rw_semaphore *sem) +{ + __down_write_nested(sem, 0); +} + +/* + * trylock for writing -- returns 1 if successful, 0 if contention + */ +int __down_write_trylock(struct rw_semaphore *sem) +{ + unsigned long flags; + int ret = 0; + + raw_spin_lock_irqsave(&sem->wait_lock, flags); + + if (sem->activity == 0) { + /* got the lock */ + sem->activity = -1; + ret = 1; + } + + raw_spin_unlock_irqrestore(&sem->wait_lock, flags); + + return ret; +} + +/* + * release a read lock on the semaphore + */ +void __up_read(struct rw_semaphore *sem) +{ + unsigned long flags; + + raw_spin_lock_irqsave(&sem->wait_lock, flags); + + if (--sem->activity == 0 && !list_empty(&sem->wait_list)) + sem = __rwsem_wake_one_writer(sem); + + raw_spin_unlock_irqrestore(&sem->wait_lock, flags); +} + +/* + * release a write lock on the semaphore + */ +void __up_write(struct rw_semaphore *sem) +{ + unsigned long flags; + + raw_spin_lock_irqsave(&sem->wait_lock, flags); + + sem->activity = 0; + if (!list_empty(&sem->wait_list)) + sem = __rwsem_do_wake(sem, 1); + + raw_spin_unlock_irqrestore(&sem->wait_lock, flags); +} + +/* + * downgrade a write lock into a read lock + * - just wake up any readers at the front of the queue + */ +void __downgrade_write(struct rw_semaphore *sem) +{ + unsigned long flags; + + raw_spin_lock_irqsave(&sem->wait_lock, flags); + + sem->activity = 1; + if (!list_empty(&sem->wait_list)) + sem = __rwsem_do_wake(sem, 0); + + raw_spin_unlock_irqrestore(&sem->wait_lock, flags); +} + diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c new file mode 100644 index 0000000..19c5fa9 --- /dev/null +++ b/kernel/locking/rwsem-xadd.c @@ -0,0 +1,293 @@ +/* rwsem.c: R/W semaphores: contention handling functions + * + * Written by David Howells (dhowells@redhat.com). + * Derived from arch/i386/kernel/semaphore.c + * + * Writer lock-stealing by Alex Shi + * and Michel Lespinasse + */ +#include +#include +#include +#include + +/* + * Initialize an rwsem: + */ +void __init_rwsem(struct rw_semaphore *sem, const char *name, + struct lock_class_key *key) +{ +#ifdef CONFIG_DEBUG_LOCK_ALLOC + /* + * Make sure we are not reinitializing a held semaphore: + */ + debug_check_no_locks_freed((void *)sem, sizeof(*sem)); + lockdep_init_map(&sem->dep_map, name, key, 0); +#endif + sem->count = RWSEM_UNLOCKED_VALUE; + raw_spin_lock_init(&sem->wait_lock); + INIT_LIST_HEAD(&sem->wait_list); +} + +EXPORT_SYMBOL(__init_rwsem); + +enum rwsem_waiter_type { + RWSEM_WAITING_FOR_WRITE, + RWSEM_WAITING_FOR_READ +}; + +struct rwsem_waiter { + struct list_head list; + struct task_struct *task; + enum rwsem_waiter_type type; +}; + +enum rwsem_wake_type { + RWSEM_WAKE_ANY, /* Wake whatever's at head of wait list */ + RWSEM_WAKE_READERS, /* Wake readers only */ + RWSEM_WAKE_READ_OWNED /* Waker thread holds the read lock */ +}; + +/* + * handle the lock release when processes blocked on it that can now run + * - if we come here from up_xxxx(), then: + * - the 'active part' of count (&0x0000ffff) reached 0 (but may have changed) + * - the 'waiting part' of count (&0xffff0000) is -ve (and will still be so) + * - there must be someone on the queue + * - the spinlock must be held by the caller + * - woken process blocks are discarded from the list after having task zeroed + * - writers are only woken if downgrading is false + */ +static struct rw_semaphore * +__rwsem_do_wake(struct rw_semaphore *sem, enum rwsem_wake_type wake_type) +{ + struct rwsem_waiter *waiter; + struct task_struct *tsk; + struct list_head *next; + long oldcount, woken, loop, adjustment; + + waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); + if (waiter->type == RWSEM_WAITING_FOR_WRITE) { + if (wake_type == RWSEM_WAKE_ANY) + /* Wake writer at the front of the queue, but do not + * grant it the lock yet as we want other writers + * to be able to steal it. Readers, on the other hand, + * will block as they will notice the queued writer. + */ + wake_up_process(waiter->task); + goto out; + } + + /* Writers might steal the lock before we grant it to the next reader. + * We prefer to do the first reader grant before counting readers + * so we can bail out early if a writer stole the lock. + */ + adjustment = 0; + if (wake_type != RWSEM_WAKE_READ_OWNED) { + adjustment = RWSEM_ACTIVE_READ_BIAS; + try_reader_grant: + oldcount = rwsem_atomic_update(adjustment, sem) - adjustment; + if (unlikely(oldcount < RWSEM_WAITING_BIAS)) { + /* A writer stole the lock. Undo our reader grant. */ + if (rwsem_atomic_update(-adjustment, sem) & + RWSEM_ACTIVE_MASK) + goto out; + /* Last active locker left. Retry waking readers. */ + goto try_reader_grant; + } + } + + /* Grant an infinite number of read locks to the readers at the front + * of the queue. Note we increment the 'active part' of the count by + * the number of readers before waking any processes up. + */ + woken = 0; + do { + woken++; + + if (waiter->list.next == &sem->wait_list) + break; + + waiter = list_entry(waiter->list.next, + struct rwsem_waiter, list); + + } while (waiter->type != RWSEM_WAITING_FOR_WRITE); + + adjustment = woken * RWSEM_ACTIVE_READ_BIAS - adjustment; + if (waiter->type != RWSEM_WAITING_FOR_WRITE) + /* hit end of list above */ + adjustment -= RWSEM_WAITING_BIAS; + + if (adjustment) + rwsem_atomic_add(adjustment, sem); + + next = sem->wait_list.next; + loop = woken; + do { + waiter = list_entry(next, struct rwsem_waiter, list); + next = waiter->list.next; + tsk = waiter->task; + smp_mb(); + waiter->task = NULL; + wake_up_process(tsk); + put_task_struct(tsk); + } while (--loop); + + sem->wait_list.next = next; + next->prev = &sem->wait_list; + + out: + return sem; +} + +/* + * wait for the read lock to be granted + */ +struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem) +{ + long count, adjustment = -RWSEM_ACTIVE_READ_BIAS; + struct rwsem_waiter waiter; + struct task_struct *tsk = current; + + /* set up my own style of waitqueue */ + waiter.task = tsk; + waiter.type = RWSEM_WAITING_FOR_READ; + get_task_struct(tsk); + + raw_spin_lock_irq(&sem->wait_lock); + if (list_empty(&sem->wait_list)) + adjustment += RWSEM_WAITING_BIAS; + list_add_tail(&waiter.list, &sem->wait_list); + + /* we're now waiting on the lock, but no longer actively locking */ + count = rwsem_atomic_update(adjustment, sem); + + /* If there are no active locks, wake the front queued process(es). + * + * If there are no writers and we are first in the queue, + * wake our own waiter to join the existing active readers ! + */ + if (count == RWSEM_WAITING_BIAS || + (count > RWSEM_WAITING_BIAS && + adjustment != -RWSEM_ACTIVE_READ_BIAS)) + sem = __rwsem_do_wake(sem, RWSEM_WAKE_ANY); + + raw_spin_unlock_irq(&sem->wait_lock); + + /* wait to be given the lock */ + while (true) { + set_task_state(tsk, TASK_UNINTERRUPTIBLE); + if (!waiter.task) + break; + schedule(); + } + + tsk->state = TASK_RUNNING; + + return sem; +} + +/* + * wait until we successfully acquire the write lock + */ +struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem) +{ + long count, adjustment = -RWSEM_ACTIVE_WRITE_BIAS; + struct rwsem_waiter waiter; + struct task_struct *tsk = current; + + /* set up my own style of waitqueue */ + waiter.task = tsk; + waiter.type = RWSEM_WAITING_FOR_WRITE; + + raw_spin_lock_irq(&sem->wait_lock); + if (list_empty(&sem->wait_list)) + adjustment += RWSEM_WAITING_BIAS; + list_add_tail(&waiter.list, &sem->wait_list); + + /* we're now waiting on the lock, but no longer actively locking */ + count = rwsem_atomic_update(adjustment, sem); + + /* If there were already threads queued before us and there are no + * active writers, the lock must be read owned; so we try to wake + * any read locks that were queued ahead of us. */ + if (count > RWSEM_WAITING_BIAS && + adjustment == -RWSEM_ACTIVE_WRITE_BIAS) + sem = __rwsem_do_wake(sem, RWSEM_WAKE_READERS); + + /* wait until we successfully acquire the lock */ + set_task_state(tsk, TASK_UNINTERRUPTIBLE); + while (true) { + if (!(count & RWSEM_ACTIVE_MASK)) { + /* Try acquiring the write lock. */ + count = RWSEM_ACTIVE_WRITE_BIAS; + if (!list_is_singular(&sem->wait_list)) + count += RWSEM_WAITING_BIAS; + + if (sem->count == RWSEM_WAITING_BIAS && + cmpxchg(&sem->count, RWSEM_WAITING_BIAS, count) == + RWSEM_WAITING_BIAS) + break; + } + + raw_spin_unlock_irq(&sem->wait_lock); + + /* Block until there are no active lockers. */ + do { + schedule(); + set_task_state(tsk, TASK_UNINTERRUPTIBLE); + } while ((count = sem->count) & RWSEM_ACTIVE_MASK); + + raw_spin_lock_irq(&sem->wait_lock); + } + + list_del(&waiter.list); + raw_spin_unlock_irq(&sem->wait_lock); + tsk->state = TASK_RUNNING; + + return sem; +} + +/* + * handle waking up a waiter on the semaphore + * - up_read/up_write has decremented the active part of count if we come here + */ +struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem) +{ + unsigned long flags; + + raw_spin_lock_irqsave(&sem->wait_lock, flags); + + /* do nothing if list empty */ + if (!list_empty(&sem->wait_list)) + sem = __rwsem_do_wake(sem, RWSEM_WAKE_ANY); + + raw_spin_unlock_irqrestore(&sem->wait_lock, flags); + + return sem; +} + +/* + * downgrade a write lock into a read lock + * - caller incremented waiting part of count and discovered it still negative + * - just wake up any readers at the front of the queue + */ +struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem) +{ + unsigned long flags; + + raw_spin_lock_irqsave(&sem->wait_lock, flags); + + /* do nothing if list empty */ + if (!list_empty(&sem->wait_list)) + sem = __rwsem_do_wake(sem, RWSEM_WAKE_READ_OWNED); + + raw_spin_unlock_irqrestore(&sem->wait_lock, flags); + + return sem; +} + +EXPORT_SYMBOL(rwsem_down_read_failed); +EXPORT_SYMBOL(rwsem_down_write_failed); +EXPORT_SYMBOL(rwsem_wake); +EXPORT_SYMBOL(rwsem_downgrade_wake); diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c new file mode 100644 index 0000000..cfff143 --- /dev/null +++ b/kernel/locking/rwsem.c @@ -0,0 +1,157 @@ +/* kernel/rwsem.c: R/W semaphores, public implementation + * + * Written by David Howells (dhowells@redhat.com). + * Derived from asm-i386/semaphore.h + */ + +#include +#include +#include +#include +#include + +#include + +/* + * lock for reading + */ +void __sched down_read(struct rw_semaphore *sem) +{ + might_sleep(); + rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_); + + LOCK_CONTENDED(sem, __down_read_trylock, __down_read); +} + +EXPORT_SYMBOL(down_read); + +/* + * trylock for reading -- returns 1 if successful, 0 if contention + */ +int down_read_trylock(struct rw_semaphore *sem) +{ + int ret = __down_read_trylock(sem); + + if (ret == 1) + rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_); + return ret; +} + +EXPORT_SYMBOL(down_read_trylock); + +/* + * lock for writing + */ +void __sched down_write(struct rw_semaphore *sem) +{ + might_sleep(); + rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_); + + LOCK_CONTENDED(sem, __down_write_trylock, __down_write); +} + +EXPORT_SYMBOL(down_write); + +/* + * trylock for writing -- returns 1 if successful, 0 if contention + */ +int down_write_trylock(struct rw_semaphore *sem) +{ + int ret = __down_write_trylock(sem); + + if (ret == 1) + rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_); + return ret; +} + +EXPORT_SYMBOL(down_write_trylock); + +/* + * release a read lock + */ +void up_read(struct rw_semaphore *sem) +{ + rwsem_release(&sem->dep_map, 1, _RET_IP_); + + __up_read(sem); +} + +EXPORT_SYMBOL(up_read); + +/* + * release a write lock + */ +void up_write(struct rw_semaphore *sem) +{ + rwsem_release(&sem->dep_map, 1, _RET_IP_); + + __up_write(sem); +} + +EXPORT_SYMBOL(up_write); + +/* + * downgrade write lock to read lock + */ +void downgrade_write(struct rw_semaphore *sem) +{ + /* + * lockdep: a downgraded write will live on as a write + * dependency. + */ + __downgrade_write(sem); +} + +EXPORT_SYMBOL(downgrade_write); + +#ifdef CONFIG_DEBUG_LOCK_ALLOC + +void down_read_nested(struct rw_semaphore *sem, int subclass) +{ + might_sleep(); + rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_); + + LOCK_CONTENDED(sem, __down_read_trylock, __down_read); +} + +EXPORT_SYMBOL(down_read_nested); + +void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest) +{ + might_sleep(); + rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_); + + LOCK_CONTENDED(sem, __down_write_trylock, __down_write); +} + +EXPORT_SYMBOL(_down_write_nest_lock); + +void down_read_non_owner(struct rw_semaphore *sem) +{ + might_sleep(); + + __down_read(sem); +} + +EXPORT_SYMBOL(down_read_non_owner); + +void down_write_nested(struct rw_semaphore *sem, int subclass) +{ + might_sleep(); + rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_); + + LOCK_CONTENDED(sem, __down_write_trylock, __down_write); +} + +EXPORT_SYMBOL(down_write_nested); + +void up_read_non_owner(struct rw_semaphore *sem) +{ + __up_read(sem); +} + +EXPORT_SYMBOL(up_read_non_owner); + +#endif + + diff --git a/kernel/rwsem.c b/kernel/rwsem.c deleted file mode 100644 index cfff143..0000000 --- a/kernel/rwsem.c +++ /dev/null @@ -1,157 +0,0 @@ -/* kernel/rwsem.c: R/W semaphores, public implementation - * - * Written by David Howells (dhowells@redhat.com). - * Derived from asm-i386/semaphore.h - */ - -#include -#include -#include -#include -#include - -#include - -/* - * lock for reading - */ -void __sched down_read(struct rw_semaphore *sem) -{ - might_sleep(); - rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_); - - LOCK_CONTENDED(sem, __down_read_trylock, __down_read); -} - -EXPORT_SYMBOL(down_read); - -/* - * trylock for reading -- returns 1 if successful, 0 if contention - */ -int down_read_trylock(struct rw_semaphore *sem) -{ - int ret = __down_read_trylock(sem); - - if (ret == 1) - rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_); - return ret; -} - -EXPORT_SYMBOL(down_read_trylock); - -/* - * lock for writing - */ -void __sched down_write(struct rw_semaphore *sem) -{ - might_sleep(); - rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_); - - LOCK_CONTENDED(sem, __down_write_trylock, __down_write); -} - -EXPORT_SYMBOL(down_write); - -/* - * trylock for writing -- returns 1 if successful, 0 if contention - */ -int down_write_trylock(struct rw_semaphore *sem) -{ - int ret = __down_write_trylock(sem); - - if (ret == 1) - rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_); - return ret; -} - -EXPORT_SYMBOL(down_write_trylock); - -/* - * release a read lock - */ -void up_read(struct rw_semaphore *sem) -{ - rwsem_release(&sem->dep_map, 1, _RET_IP_); - - __up_read(sem); -} - -EXPORT_SYMBOL(up_read); - -/* - * release a write lock - */ -void up_write(struct rw_semaphore *sem) -{ - rwsem_release(&sem->dep_map, 1, _RET_IP_); - - __up_write(sem); -} - -EXPORT_SYMBOL(up_write); - -/* - * downgrade write lock to read lock - */ -void downgrade_write(struct rw_semaphore *sem) -{ - /* - * lockdep: a downgraded write will live on as a write - * dependency. - */ - __downgrade_write(sem); -} - -EXPORT_SYMBOL(downgrade_write); - -#ifdef CONFIG_DEBUG_LOCK_ALLOC - -void down_read_nested(struct rw_semaphore *sem, int subclass) -{ - might_sleep(); - rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_); - - LOCK_CONTENDED(sem, __down_read_trylock, __down_read); -} - -EXPORT_SYMBOL(down_read_nested); - -void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest) -{ - might_sleep(); - rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_); - - LOCK_CONTENDED(sem, __down_write_trylock, __down_write); -} - -EXPORT_SYMBOL(_down_write_nest_lock); - -void down_read_non_owner(struct rw_semaphore *sem) -{ - might_sleep(); - - __down_read(sem); -} - -EXPORT_SYMBOL(down_read_non_owner); - -void down_write_nested(struct rw_semaphore *sem, int subclass) -{ - might_sleep(); - rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_); - - LOCK_CONTENDED(sem, __down_write_trylock, __down_write); -} - -EXPORT_SYMBOL(down_write_nested); - -void up_read_non_owner(struct rw_semaphore *sem) -{ - __up_read(sem); -} - -EXPORT_SYMBOL(up_read_non_owner); - -#endif - - diff --git a/lib/Makefile b/lib/Makefile index bee27e1..ca8cadc 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -42,8 +42,6 @@ obj-$(CONFIG_GENERIC_PCI_IOMAP) += pci_iomap.o obj-$(CONFIG_HAS_IOMEM) += iomap_copy.o devres.o obj-$(CONFIG_CHECK_SIGNATURE) += check_signature.o obj-$(CONFIG_DEBUG_LOCKING_API_SELFTESTS) += locking-selftest.o -lib-$(CONFIG_RWSEM_GENERIC_SPINLOCK) += rwsem-spinlock.o -lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o lib-$(CONFIG_PERCPU_RWSEM) += percpu-rwsem.o CFLAGS_hweight.o = $(subst $(quote),,$(CONFIG_ARCH_HWEIGHT_CFLAGS)) diff --git a/lib/rwsem-spinlock.c b/lib/rwsem-spinlock.c deleted file mode 100644 index 9be8a91..0000000 --- a/lib/rwsem-spinlock.c +++ /dev/null @@ -1,296 +0,0 @@ -/* rwsem-spinlock.c: R/W semaphores: contention handling functions for - * generic spinlock implementation - * - * Copyright (c) 2001 David Howells (dhowells@redhat.com). - * - Derived partially from idea by Andrea Arcangeli - * - Derived also from comments by Linus - */ -#include -#include -#include - -enum rwsem_waiter_type { - RWSEM_WAITING_FOR_WRITE, - RWSEM_WAITING_FOR_READ -}; - -struct rwsem_waiter { - struct list_head list; - struct task_struct *task; - enum rwsem_waiter_type type; -}; - -int rwsem_is_locked(struct rw_semaphore *sem) -{ - int ret = 1; - unsigned long flags; - - if (raw_spin_trylock_irqsave(&sem->wait_lock, flags)) { - ret = (sem->activity != 0); - raw_spin_unlock_irqrestore(&sem->wait_lock, flags); - } - return ret; -} -EXPORT_SYMBOL(rwsem_is_locked); - -/* - * initialise the semaphore - */ -void __init_rwsem(struct rw_semaphore *sem, const char *name, - struct lock_class_key *key) -{ -#ifdef CONFIG_DEBUG_LOCK_ALLOC - /* - * Make sure we are not reinitializing a held semaphore: - */ - debug_check_no_locks_freed((void *)sem, sizeof(*sem)); - lockdep_init_map(&sem->dep_map, name, key, 0); -#endif - sem->activity = 0; - raw_spin_lock_init(&sem->wait_lock); - INIT_LIST_HEAD(&sem->wait_list); -} -EXPORT_SYMBOL(__init_rwsem); - -/* - * handle the lock release when processes blocked on it that can now run - * - if we come here, then: - * - the 'active count' _reached_ zero - * - the 'waiting count' is non-zero - * - the spinlock must be held by the caller - * - woken process blocks are discarded from the list after having task zeroed - * - writers are only woken if wakewrite is non-zero - */ -static inline struct rw_semaphore * -__rwsem_do_wake(struct rw_semaphore *sem, int wakewrite) -{ - struct rwsem_waiter *waiter; - struct task_struct *tsk; - int woken; - - waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); - - if (waiter->type == RWSEM_WAITING_FOR_WRITE) { - if (wakewrite) - /* Wake up a writer. Note that we do not grant it the - * lock - it will have to acquire it when it runs. */ - wake_up_process(waiter->task); - goto out; - } - - /* grant an infinite number of read locks to the front of the queue */ - woken = 0; - do { - struct list_head *next = waiter->list.next; - - list_del(&waiter->list); - tsk = waiter->task; - smp_mb(); - waiter->task = NULL; - wake_up_process(tsk); - put_task_struct(tsk); - woken++; - if (next == &sem->wait_list) - break; - waiter = list_entry(next, struct rwsem_waiter, list); - } while (waiter->type != RWSEM_WAITING_FOR_WRITE); - - sem->activity += woken; - - out: - return sem; -} - -/* - * wake a single writer - */ -static inline struct rw_semaphore * -__rwsem_wake_one_writer(struct rw_semaphore *sem) -{ - struct rwsem_waiter *waiter; - - waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); - wake_up_process(waiter->task); - - return sem; -} - -/* - * get a read lock on the semaphore - */ -void __sched __down_read(struct rw_semaphore *sem) -{ - struct rwsem_waiter waiter; - struct task_struct *tsk; - unsigned long flags; - - raw_spin_lock_irqsave(&sem->wait_lock, flags); - - if (sem->activity >= 0 && list_empty(&sem->wait_list)) { - /* granted */ - sem->activity++; - raw_spin_unlock_irqrestore(&sem->wait_lock, flags); - goto out; - } - - tsk = current; - set_task_state(tsk, TASK_UNINTERRUPTIBLE); - - /* set up my own style of waitqueue */ - waiter.task = tsk; - waiter.type = RWSEM_WAITING_FOR_READ; - get_task_struct(tsk); - - list_add_tail(&waiter.list, &sem->wait_list); - - /* we don't need to touch the semaphore struct anymore */ - raw_spin_unlock_irqrestore(&sem->wait_lock, flags); - - /* wait to be given the lock */ - for (;;) { - if (!waiter.task) - break; - schedule(); - set_task_state(tsk, TASK_UNINTERRUPTIBLE); - } - - tsk->state = TASK_RUNNING; - out: - ; -} - -/* - * trylock for reading -- returns 1 if successful, 0 if contention - */ -int __down_read_trylock(struct rw_semaphore *sem) -{ - unsigned long flags; - int ret = 0; - - - raw_spin_lock_irqsave(&sem->wait_lock, flags); - - if (sem->activity >= 0 && list_empty(&sem->wait_list)) { - /* granted */ - sem->activity++; - ret = 1; - } - - raw_spin_unlock_irqrestore(&sem->wait_lock, flags); - - return ret; -} - -/* - * get a write lock on the semaphore - */ -void __sched __down_write_nested(struct rw_semaphore *sem, int subclass) -{ - struct rwsem_waiter waiter; - struct task_struct *tsk; - unsigned long flags; - - raw_spin_lock_irqsave(&sem->wait_lock, flags); - - /* set up my own style of waitqueue */ - tsk = current; - waiter.task = tsk; - waiter.type = RWSEM_WAITING_FOR_WRITE; - list_add_tail(&waiter.list, &sem->wait_list); - - /* wait for someone to release the lock */ - for (;;) { - /* - * That is the key to support write lock stealing: allows the - * task already on CPU to get the lock soon rather than put - * itself into sleep and waiting for system woke it or someone - * else in the head of the wait list up. - */ - if (sem->activity == 0) - break; - set_task_state(tsk, TASK_UNINTERRUPTIBLE); - raw_spin_unlock_irqrestore(&sem->wait_lock, flags); - schedule(); - raw_spin_lock_irqsave(&sem->wait_lock, flags); - } - /* got the lock */ - sem->activity = -1; - list_del(&waiter.list); - - raw_spin_unlock_irqrestore(&sem->wait_lock, flags); -} - -void __sched __down_write(struct rw_semaphore *sem) -{ - __down_write_nested(sem, 0); -} - -/* - * trylock for writing -- returns 1 if successful, 0 if contention - */ -int __down_write_trylock(struct rw_semaphore *sem) -{ - unsigned long flags; - int ret = 0; - - raw_spin_lock_irqsave(&sem->wait_lock, flags); - - if (sem->activity == 0) { - /* got the lock */ - sem->activity = -1; - ret = 1; - } - - raw_spin_unlock_irqrestore(&sem->wait_lock, flags); - - return ret; -} - -/* - * release a read lock on the semaphore - */ -void __up_read(struct rw_semaphore *sem) -{ - unsigned long flags; - - raw_spin_lock_irqsave(&sem->wait_lock, flags); - - if (--sem->activity == 0 && !list_empty(&sem->wait_list)) - sem = __rwsem_wake_one_writer(sem); - - raw_spin_unlock_irqrestore(&sem->wait_lock, flags); -} - -/* - * release a write lock on the semaphore - */ -void __up_write(struct rw_semaphore *sem) -{ - unsigned long flags; - - raw_spin_lock_irqsave(&sem->wait_lock, flags); - - sem->activity = 0; - if (!list_empty(&sem->wait_list)) - sem = __rwsem_do_wake(sem, 1); - - raw_spin_unlock_irqrestore(&sem->wait_lock, flags); -} - -/* - * downgrade a write lock into a read lock - * - just wake up any readers at the front of the queue - */ -void __downgrade_write(struct rw_semaphore *sem) -{ - unsigned long flags; - - raw_spin_lock_irqsave(&sem->wait_lock, flags); - - sem->activity = 1; - if (!list_empty(&sem->wait_list)) - sem = __rwsem_do_wake(sem, 0); - - raw_spin_unlock_irqrestore(&sem->wait_lock, flags); -} - diff --git a/lib/rwsem.c b/lib/rwsem.c deleted file mode 100644 index 19c5fa9..0000000 --- a/lib/rwsem.c +++ /dev/null @@ -1,293 +0,0 @@ -/* rwsem.c: R/W semaphores: contention handling functions - * - * Written by David Howells (dhowells@redhat.com). - * Derived from arch/i386/kernel/semaphore.c - * - * Writer lock-stealing by Alex Shi - * and Michel Lespinasse - */ -#include -#include -#include -#include - -/* - * Initialize an rwsem: - */ -void __init_rwsem(struct rw_semaphore *sem, const char *name, - struct lock_class_key *key) -{ -#ifdef CONFIG_DEBUG_LOCK_ALLOC - /* - * Make sure we are not reinitializing a held semaphore: - */ - debug_check_no_locks_freed((void *)sem, sizeof(*sem)); - lockdep_init_map(&sem->dep_map, name, key, 0); -#endif - sem->count = RWSEM_UNLOCKED_VALUE; - raw_spin_lock_init(&sem->wait_lock); - INIT_LIST_HEAD(&sem->wait_list); -} - -EXPORT_SYMBOL(__init_rwsem); - -enum rwsem_waiter_type { - RWSEM_WAITING_FOR_WRITE, - RWSEM_WAITING_FOR_READ -}; - -struct rwsem_waiter { - struct list_head list; - struct task_struct *task; - enum rwsem_waiter_type type; -}; - -enum rwsem_wake_type { - RWSEM_WAKE_ANY, /* Wake whatever's at head of wait list */ - RWSEM_WAKE_READERS, /* Wake readers only */ - RWSEM_WAKE_READ_OWNED /* Waker thread holds the read lock */ -}; - -/* - * handle the lock release when processes blocked on it that can now run - * - if we come here from up_xxxx(), then: - * - the 'active part' of count (&0x0000ffff) reached 0 (but may have changed) - * - the 'waiting part' of count (&0xffff0000) is -ve (and will still be so) - * - there must be someone on the queue - * - the spinlock must be held by the caller - * - woken process blocks are discarded from the list after having task zeroed - * - writers are only woken if downgrading is false - */ -static struct rw_semaphore * -__rwsem_do_wake(struct rw_semaphore *sem, enum rwsem_wake_type wake_type) -{ - struct rwsem_waiter *waiter; - struct task_struct *tsk; - struct list_head *next; - long oldcount, woken, loop, adjustment; - - waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); - if (waiter->type == RWSEM_WAITING_FOR_WRITE) { - if (wake_type == RWSEM_WAKE_ANY) - /* Wake writer at the front of the queue, but do not - * grant it the lock yet as we want other writers - * to be able to steal it. Readers, on the other hand, - * will block as they will notice the queued writer. - */ - wake_up_process(waiter->task); - goto out; - } - - /* Writers might steal the lock before we grant it to the next reader. - * We prefer to do the first reader grant before counting readers - * so we can bail out early if a writer stole the lock. - */ - adjustment = 0; - if (wake_type != RWSEM_WAKE_READ_OWNED) { - adjustment = RWSEM_ACTIVE_READ_BIAS; - try_reader_grant: - oldcount = rwsem_atomic_update(adjustment, sem) - adjustment; - if (unlikely(oldcount < RWSEM_WAITING_BIAS)) { - /* A writer stole the lock. Undo our reader grant. */ - if (rwsem_atomic_update(-adjustment, sem) & - RWSEM_ACTIVE_MASK) - goto out; - /* Last active locker left. Retry waking readers. */ - goto try_reader_grant; - } - } - - /* Grant an infinite number of read locks to the readers at the front - * of the queue. Note we increment the 'active part' of the count by - * the number of readers before waking any processes up. - */ - woken = 0; - do { - woken++; - - if (waiter->list.next == &sem->wait_list) - break; - - waiter = list_entry(waiter->list.next, - struct rwsem_waiter, list); - - } while (waiter->type != RWSEM_WAITING_FOR_WRITE); - - adjustment = woken * RWSEM_ACTIVE_READ_BIAS - adjustment; - if (waiter->type != RWSEM_WAITING_FOR_WRITE) - /* hit end of list above */ - adjustment -= RWSEM_WAITING_BIAS; - - if (adjustment) - rwsem_atomic_add(adjustment, sem); - - next = sem->wait_list.next; - loop = woken; - do { - waiter = list_entry(next, struct rwsem_waiter, list); - next = waiter->list.next; - tsk = waiter->task; - smp_mb(); - waiter->task = NULL; - wake_up_process(tsk); - put_task_struct(tsk); - } while (--loop); - - sem->wait_list.next = next; - next->prev = &sem->wait_list; - - out: - return sem; -} - -/* - * wait for the read lock to be granted - */ -struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem) -{ - long count, adjustment = -RWSEM_ACTIVE_READ_BIAS; - struct rwsem_waiter waiter; - struct task_struct *tsk = current; - - /* set up my own style of waitqueue */ - waiter.task = tsk; - waiter.type = RWSEM_WAITING_FOR_READ; - get_task_struct(tsk); - - raw_spin_lock_irq(&sem->wait_lock); - if (list_empty(&sem->wait_list)) - adjustment += RWSEM_WAITING_BIAS; - list_add_tail(&waiter.list, &sem->wait_list); - - /* we're now waiting on the lock, but no longer actively locking */ - count = rwsem_atomic_update(adjustment, sem); - - /* If there are no active locks, wake the front queued process(es). - * - * If there are no writers and we are first in the queue, - * wake our own waiter to join the existing active readers ! - */ - if (count == RWSEM_WAITING_BIAS || - (count > RWSEM_WAITING_BIAS && - adjustment != -RWSEM_ACTIVE_READ_BIAS)) - sem = __rwsem_do_wake(sem, RWSEM_WAKE_ANY); - - raw_spin_unlock_irq(&sem->wait_lock); - - /* wait to be given the lock */ - while (true) { - set_task_state(tsk, TASK_UNINTERRUPTIBLE); - if (!waiter.task) - break; - schedule(); - } - - tsk->state = TASK_RUNNING; - - return sem; -} - -/* - * wait until we successfully acquire the write lock - */ -struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem) -{ - long count, adjustment = -RWSEM_ACTIVE_WRITE_BIAS; - struct rwsem_waiter waiter; - struct task_struct *tsk = current; - - /* set up my own style of waitqueue */ - waiter.task = tsk; - waiter.type = RWSEM_WAITING_FOR_WRITE; - - raw_spin_lock_irq(&sem->wait_lock); - if (list_empty(&sem->wait_list)) - adjustment += RWSEM_WAITING_BIAS; - list_add_tail(&waiter.list, &sem->wait_list); - - /* we're now waiting on the lock, but no longer actively locking */ - count = rwsem_atomic_update(adjustment, sem); - - /* If there were already threads queued before us and there are no - * active writers, the lock must be read owned; so we try to wake - * any read locks that were queued ahead of us. */ - if (count > RWSEM_WAITING_BIAS && - adjustment == -RWSEM_ACTIVE_WRITE_BIAS) - sem = __rwsem_do_wake(sem, RWSEM_WAKE_READERS); - - /* wait until we successfully acquire the lock */ - set_task_state(tsk, TASK_UNINTERRUPTIBLE); - while (true) { - if (!(count & RWSEM_ACTIVE_MASK)) { - /* Try acquiring the write lock. */ - count = RWSEM_ACTIVE_WRITE_BIAS; - if (!list_is_singular(&sem->wait_list)) - count += RWSEM_WAITING_BIAS; - - if (sem->count == RWSEM_WAITING_BIAS && - cmpxchg(&sem->count, RWSEM_WAITING_BIAS, count) == - RWSEM_WAITING_BIAS) - break; - } - - raw_spin_unlock_irq(&sem->wait_lock); - - /* Block until there are no active lockers. */ - do { - schedule(); - set_task_state(tsk, TASK_UNINTERRUPTIBLE); - } while ((count = sem->count) & RWSEM_ACTIVE_MASK); - - raw_spin_lock_irq(&sem->wait_lock); - } - - list_del(&waiter.list); - raw_spin_unlock_irq(&sem->wait_lock); - tsk->state = TASK_RUNNING; - - return sem; -} - -/* - * handle waking up a waiter on the semaphore - * - up_read/up_write has decremented the active part of count if we come here - */ -struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem) -{ - unsigned long flags; - - raw_spin_lock_irqsave(&sem->wait_lock, flags); - - /* do nothing if list empty */ - if (!list_empty(&sem->wait_list)) - sem = __rwsem_do_wake(sem, RWSEM_WAKE_ANY); - - raw_spin_unlock_irqrestore(&sem->wait_lock, flags); - - return sem; -} - -/* - * downgrade a write lock into a read lock - * - caller incremented waiting part of count and discovered it still negative - * - just wake up any readers at the front of the queue - */ -struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem) -{ - unsigned long flags; - - raw_spin_lock_irqsave(&sem->wait_lock, flags); - - /* do nothing if list empty */ - if (!list_empty(&sem->wait_list)) - sem = __rwsem_do_wake(sem, RWSEM_WAKE_READ_OWNED); - - raw_spin_unlock_irqrestore(&sem->wait_lock, flags); - - return sem; -} - -EXPORT_SYMBOL(rwsem_down_read_failed); -EXPORT_SYMBOL(rwsem_down_write_failed); -EXPORT_SYMBOL(rwsem_wake); -EXPORT_SYMBOL(rwsem_downgrade_wake); -- cgit v0.10.2