drivers/tty/tty_ldsem.c - third_party/kernel - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Ldisc rw semaphore
  *
  * The ldisc semaphore is semantically a rw_semaphore but which enforces
  * an alternate policy, namely:
  *   1) Supports lock wait timeouts
  *   2) Write waiter has priority
  *   3) Downgrading is not supported
  *
  * Implementation notes:
  *   1) Upper half of semaphore count is a wait count (differs from rwsem
  *	in that rwsem normalizes the upper half to the wait bias)
  *   2) Lacks overflow checking
  *
  * The generic counting was copied and modified from include/asm-generic/rwsem.h
  * by Paul Mackerras <paulus@samba.org>.
  *
  * The scheduling policy was copied and modified from lib/rwsem.c
  * Written by David Howells (dhowells@redhat.com).
  *
  * This implementation incorporates the write lock stealing work of
  * Michel Lespinasse <walken@google.com>.
  *
  * Copyright (C) 2013 Peter Hurley <peter@hurleysoftware.com>
  */

 #include <linux/list.h>
 #include <linux/spinlock.h>
 #include <linux/atomic.h>
 #include <linux/tty.h>
 #include <linux/sched.h>
 #include <linux/sched/debug.h>
 #include <linux/sched/task.h>


 #if BITS_PER_LONG == 64
 # define LDSEM_ACTIVE_MASK	0xffffffffL
 #else
 # define LDSEM_ACTIVE_MASK	0x0000ffffL
 #endif

 #define LDSEM_UNLOCKED		0L
 #define LDSEM_ACTIVE_BIAS	1L
 #define LDSEM_WAIT_BIAS		(-LDSEM_ACTIVE_MASK-1)
 #define LDSEM_READ_BIAS		LDSEM_ACTIVE_BIAS
 #define LDSEM_WRITE_BIAS	(LDSEM_WAIT_BIAS + LDSEM_ACTIVE_BIAS)

 struct ldsem_waiter {
 	struct list_head list;
 	struct task_struct *task;
 };

 /*
  * Initialize an ldsem:
  */
 void __init_ldsem(struct ld_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
 	atomic_long_set(&sem->count, LDSEM_UNLOCKED);
 	sem->wait_readers = 0;
 	raw_spin_lock_init(&sem->wait_lock);
 	INIT_LIST_HEAD(&sem->read_wait);
 	INIT_LIST_HEAD(&sem->write_wait);
 }

 static void __ldsem_wake_readers(struct ld_semaphore *sem)
 {
 	struct ldsem_waiter *waiter, *next;
 	struct task_struct *tsk;
 	long adjust, count;

 	/*
 	 * Try to grant read locks to all readers on the read wait list.
 	 * Note the 'active part' of the count is incremented by
 	 * the number of readers before waking any processes up.
 	 */
 	adjust = sem->wait_readers * (LDSEM_ACTIVE_BIAS - LDSEM_WAIT_BIAS);
 	count = atomic_long_add_return(adjust, &sem->count);
 	do {
 		if (count > 0)
 			break;
 		if (atomic_long_try_cmpxchg(&sem->count, &count, count - adjust))
 			return;
 	} while (1);

 	list_for_each_entry_safe(waiter, next, &sem->read_wait, list) {
 		tsk = waiter->task;
 		smp_store_release(&waiter->task, NULL);
 		wake_up_process(tsk);
 		put_task_struct(tsk);
 	}
 	INIT_LIST_HEAD(&sem->read_wait);
 	sem->wait_readers = 0;
 }

 static inline int writer_trylock(struct ld_semaphore *sem)
 {
 	/*
 	 * Only wake this writer if the active part of the count can be
 	 * transitioned from 0 -> 1
 	 */
 	long count = atomic_long_add_return(LDSEM_ACTIVE_BIAS, &sem->count);
 	do {
 		if ((count & LDSEM_ACTIVE_MASK) == LDSEM_ACTIVE_BIAS)
 			return 1;
 		if (atomic_long_try_cmpxchg(&sem->count, &count, count - LDSEM_ACTIVE_BIAS))
 			return 0;
 	} while (1);
 }

 static void __ldsem_wake_writer(struct ld_semaphore *sem)
 {
 	struct ldsem_waiter *waiter;

 	waiter = list_entry(sem->write_wait.next, struct ldsem_waiter, list);
 	wake_up_process(waiter->task);
 }

 /*
  * 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)
  * - the spinlock must be held by the caller
  * - woken process blocks are discarded from the list after having task zeroed
  */
 static void __ldsem_wake(struct ld_semaphore *sem)
 {
 	if (!list_empty(&sem->write_wait))
 		__ldsem_wake_writer(sem);
 	else if (!list_empty(&sem->read_wait))
 		__ldsem_wake_readers(sem);
 }

 static void ldsem_wake(struct ld_semaphore *sem)
 {
 	unsigned long flags;

 	raw_spin_lock_irqsave(&sem->wait_lock, flags);
 	__ldsem_wake(sem);
 	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
 }

 /*
  * wait for the read lock to be granted
  */
 static struct ld_semaphore __sched *
 down_read_failed(struct ld_semaphore *sem, long count, long timeout)
 {
 	struct ldsem_waiter waiter;
 	long adjust = -LDSEM_ACTIVE_BIAS + LDSEM_WAIT_BIAS;

 	/* set up my own style of waitqueue */
 	raw_spin_lock_irq(&sem->wait_lock);

 	/*
 	 * Try to reverse the lock attempt but if the count has changed
 	 * so that reversing fails, check if there are are no waiters,
 	 * and early-out if not
 	 */
 	do {
 		if (atomic_long_try_cmpxchg(&sem->count, &count, count + adjust)) {
 			count += adjust;
 			break;
 		}
 		if (count > 0) {
 			raw_spin_unlock_irq(&sem->wait_lock);
 			return sem;
 		}
 	} while (1);

 	list_add_tail(&waiter.list, &sem->read_wait);
 	sem->wait_readers++;

 	waiter.task = current;
 	get_task_struct(current);

 	/* if there are no active locks, wake the new lock owner(s) */
 	if ((count & LDSEM_ACTIVE_MASK) == 0)
 		__ldsem_wake(sem);

 	raw_spin_unlock_irq(&sem->wait_lock);

 	/* wait to be given the lock */
 	for (;;) {
 		set_current_state(TASK_UNINTERRUPTIBLE);

 		if (!smp_load_acquire(&waiter.task))
 			break;
 		if (!timeout)
 			break;
 		timeout = schedule_timeout(timeout);
 	}

 	__set_current_state(TASK_RUNNING);

 	if (!timeout) {
 		/*
 		 * Lock timed out but check if this task was just
 		 * granted lock ownership - if so, pretend there
 		 * was no timeout; otherwise, cleanup lock wait.
 		 */
 		raw_spin_lock_irq(&sem->wait_lock);
 		if (waiter.task) {
 			atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count);
 			sem->wait_readers--;
 			list_del(&waiter.list);
 			raw_spin_unlock_irq(&sem->wait_lock);
 			put_task_struct(waiter.task);
 			return NULL;
 		}
 		raw_spin_unlock_irq(&sem->wait_lock);
 	}

 	return sem;
 }

 /*
  * wait for the write lock to be granted
  */
 static struct ld_semaphore __sched *
 down_write_failed(struct ld_semaphore *sem, long count, long timeout)
 {
 	struct ldsem_waiter waiter;
 	long adjust = -LDSEM_ACTIVE_BIAS;
 	int locked = 0;

 	/* set up my own style of waitqueue */
 	raw_spin_lock_irq(&sem->wait_lock);

 	/*
 	 * Try to reverse the lock attempt but if the count has changed
 	 * so that reversing fails, check if the lock is now owned,
 	 * and early-out if so.
 	 */
 	do {
 		if (atomic_long_try_cmpxchg(&sem->count, &count, count + adjust))
 			break;
 		if ((count & LDSEM_ACTIVE_MASK) == LDSEM_ACTIVE_BIAS) {
 			raw_spin_unlock_irq(&sem->wait_lock);
 			return sem;
 		}
 	} while (1);

 	list_add_tail(&waiter.list, &sem->write_wait);

 	waiter.task = current;

 	set_current_state(TASK_UNINTERRUPTIBLE);
 	for (;;) {
 		if (!timeout)
 			break;
 		raw_spin_unlock_irq(&sem->wait_lock);
 		timeout = schedule_timeout(timeout);
 		raw_spin_lock_irq(&sem->wait_lock);
 		set_current_state(TASK_UNINTERRUPTIBLE);
 		locked = writer_trylock(sem);
 		if (locked)
 			break;
 	}

 	if (!locked)
 		atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count);
 	list_del(&waiter.list);

 	/*
 	 * In case of timeout, wake up every reader who gave the right of way
 	 * to writer. Prevent separation readers into two groups:
 	 * one that helds semaphore and another that sleeps.
 	 * (in case of no contention with a writer)
 	 */
 	if (!locked && list_empty(&sem->write_wait))
 		__ldsem_wake_readers(sem);

 	raw_spin_unlock_irq(&sem->wait_lock);

 	__set_current_state(TASK_RUNNING);

 	/* lock wait may have timed out */
 	if (!locked)
 		return NULL;
 	return sem;
 }


 static int __ldsem_down_read_nested(struct ld_semaphore *sem,
 					   int subclass, long timeout)
 {
 	long count;

 	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);

 	count = atomic_long_add_return(LDSEM_READ_BIAS, &sem->count);
 	if (count <= 0) {
 		lock_contended(&sem->dep_map, _RET_IP_);
 		if (!down_read_failed(sem, count, timeout)) {
 			rwsem_release(&sem->dep_map, 1, _RET_IP_);
 			return 0;
 		}
 	}
 	lock_acquired(&sem->dep_map, _RET_IP_);
 	return 1;
 }

 static int __ldsem_down_write_nested(struct ld_semaphore *sem,
 					    int subclass, long timeout)
 {
 	long count;

 	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);

 	count = atomic_long_add_return(LDSEM_WRITE_BIAS, &sem->count);
 	if ((count & LDSEM_ACTIVE_MASK) != LDSEM_ACTIVE_BIAS) {
 		lock_contended(&sem->dep_map, _RET_IP_);
 		if (!down_write_failed(sem, count, timeout)) {
 			rwsem_release(&sem->dep_map, 1, _RET_IP_);
 			return 0;
 		}
 	}
 	lock_acquired(&sem->dep_map, _RET_IP_);
 	return 1;
 }


 /*
  * lock for reading -- returns 1 if successful, 0 if timed out
  */
 int __sched ldsem_down_read(struct ld_semaphore *sem, long timeout)
 {
 	might_sleep();
 	return __ldsem_down_read_nested(sem, 0, timeout);
 }

 /*
  * trylock for reading -- returns 1 if successful, 0 if contention
  */
 int ldsem_down_read_trylock(struct ld_semaphore *sem)
 {
 	long count = atomic_long_read(&sem->count);

 	while (count >= 0) {
 		if (atomic_long_try_cmpxchg(&sem->count, &count, count + LDSEM_READ_BIAS)) {
 			rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
 			lock_acquired(&sem->dep_map, _RET_IP_);
 			return 1;
 		}
 	}
 	return 0;
 }

 /*
  * lock for writing -- returns 1 if successful, 0 if timed out
  */
 int __sched ldsem_down_write(struct ld_semaphore *sem, long timeout)
 {
 	might_sleep();
 	return __ldsem_down_write_nested(sem, 0, timeout);
 }

 /*
  * trylock for writing -- returns 1 if successful, 0 if contention
  */
 int ldsem_down_write_trylock(struct ld_semaphore *sem)
 {
 	long count = atomic_long_read(&sem->count);

 	while ((count & LDSEM_ACTIVE_MASK) == 0) {
 		if (atomic_long_try_cmpxchg(&sem->count, &count, count + LDSEM_WRITE_BIAS)) {
 			rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
 			lock_acquired(&sem->dep_map, _RET_IP_);
 			return 1;
 		}
 	}
 	return 0;
 }

 /*
  * release a read lock
  */
 void ldsem_up_read(struct ld_semaphore *sem)
 {
 	long count;

 	rwsem_release(&sem->dep_map, 1, _RET_IP_);

 	count = atomic_long_add_return(-LDSEM_READ_BIAS, &sem->count);
 	if (count < 0 && (count & LDSEM_ACTIVE_MASK) == 0)
 		ldsem_wake(sem);
 }

 /*
  * release a write lock
  */
 void ldsem_up_write(struct ld_semaphore *sem)
 {
 	long count;

 	rwsem_release(&sem->dep_map, 1, _RET_IP_);

 	count = atomic_long_add_return(-LDSEM_WRITE_BIAS, &sem->count);
 	if (count < 0)
 		ldsem_wake(sem);
 }


 #ifdef CONFIG_DEBUG_LOCK_ALLOC

 int ldsem_down_read_nested(struct ld_semaphore *sem, int subclass, long timeout)
 {
 	might_sleep();
 	return __ldsem_down_read_nested(sem, subclass, timeout);
 }

 int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
 			    long timeout)
 {
 	might_sleep();
 	return __ldsem_down_write_nested(sem, subclass, timeout);
 }

 #endif
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Ldisc rw semaphore
	*
	* The ldisc semaphore is semantically a rw_semaphore but which enforces
	* an alternate policy, namely:
	* 1) Supports lock wait timeouts
	* 2) Write waiter has priority
	* 3) Downgrading is not supported
	*
	* Implementation notes:
	* 1) Upper half of semaphore count is a wait count (differs from rwsem
	* in that rwsem normalizes the upper half to the wait bias)
	* 2) Lacks overflow checking
	*
	* The generic counting was copied and modified from include/asm-generic/rwsem.h
	* by Paul Mackerras <paulus@samba.org>.
	*
	* The scheduling policy was copied and modified from lib/rwsem.c
	* Written by David Howells (dhowells@redhat.com).
	*
	* This implementation incorporates the write lock stealing work of
	* Michel Lespinasse <walken@google.com>.
	*
	* Copyright (C) 2013 Peter Hurley <peter@hurleysoftware.com>
	*/

	#include <linux/list.h>
	#include <linux/spinlock.h>
	#include <linux/atomic.h>
	#include <linux/tty.h>
	#include <linux/sched.h>
	#include <linux/sched/debug.h>
	#include <linux/sched/task.h>


	#if BITS_PER_LONG == 64
	# define LDSEM_ACTIVE_MASK 0xffffffffL
	#else
	# define LDSEM_ACTIVE_MASK 0x0000ffffL
	#endif

	#define LDSEM_UNLOCKED 0L
	#define LDSEM_ACTIVE_BIAS 1L
	#define LDSEM_WAIT_BIAS (-LDSEM_ACTIVE_MASK-1)
	#define LDSEM_READ_BIAS LDSEM_ACTIVE_BIAS
	#define LDSEM_WRITE_BIAS (LDSEM_WAIT_BIAS + LDSEM_ACTIVE_BIAS)

	struct ldsem_waiter {
	struct list_head list;
	struct task_struct *task;
	};

	/*
	* Initialize an ldsem:
	*/
	void __init_ldsem(struct ld_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
	atomic_long_set(&sem->count, LDSEM_UNLOCKED);
	sem->wait_readers = 0;
	raw_spin_lock_init(&sem->wait_lock);
	INIT_LIST_HEAD(&sem->read_wait);
	INIT_LIST_HEAD(&sem->write_wait);
	}

	static void __ldsem_wake_readers(struct ld_semaphore *sem)
	{
	struct ldsem_waiter waiter, next;
	struct task_struct *tsk;
	long adjust, count;

	/*
	* Try to grant read locks to all readers on the read wait list.
	* Note the 'active part' of the count is incremented by
	* the number of readers before waking any processes up.
	*/
	adjust = sem->wait_readers * (LDSEM_ACTIVE_BIAS - LDSEM_WAIT_BIAS);
	count = atomic_long_add_return(adjust, &sem->count);
	do {
	if (count > 0)
	break;
	if (atomic_long_try_cmpxchg(&sem->count, &count, count - adjust))
	return;
	} while (1);

	list_for_each_entry_safe(waiter, next, &sem->read_wait, list) {
	tsk = waiter->task;
	smp_store_release(&waiter->task, NULL);
	wake_up_process(tsk);
	put_task_struct(tsk);
	}
	INIT_LIST_HEAD(&sem->read_wait);
	sem->wait_readers = 0;
	}

	static inline int writer_trylock(struct ld_semaphore *sem)
	{
	/*
	* Only wake this writer if the active part of the count can be
	* transitioned from 0 -> 1
	*/
	long count = atomic_long_add_return(LDSEM_ACTIVE_BIAS, &sem->count);
	do {
	if ((count & LDSEM_ACTIVE_MASK) == LDSEM_ACTIVE_BIAS)
	return 1;
	if (atomic_long_try_cmpxchg(&sem->count, &count, count - LDSEM_ACTIVE_BIAS))
	return 0;
	} while (1);
	}

	static void __ldsem_wake_writer(struct ld_semaphore *sem)
	{
	struct ldsem_waiter *waiter;

	waiter = list_entry(sem->write_wait.next, struct ldsem_waiter, list);
	wake_up_process(waiter->task);
	}

	/*
	* 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)
	* - the spinlock must be held by the caller
	* - woken process blocks are discarded from the list after having task zeroed
	*/
	static void __ldsem_wake(struct ld_semaphore *sem)
	{
	if (!list_empty(&sem->write_wait))
	__ldsem_wake_writer(sem);
	else if (!list_empty(&sem->read_wait))
	__ldsem_wake_readers(sem);
	}

	static void ldsem_wake(struct ld_semaphore *sem)
	{
	unsigned long flags;

	raw_spin_lock_irqsave(&sem->wait_lock, flags);
	__ldsem_wake(sem);
	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
	}

	/*
	* wait for the read lock to be granted
	*/
	static struct ld_semaphore __sched *
	down_read_failed(struct ld_semaphore *sem, long count, long timeout)
	{
	struct ldsem_waiter waiter;
	long adjust = -LDSEM_ACTIVE_BIAS + LDSEM_WAIT_BIAS;

	/* set up my own style of waitqueue */
	raw_spin_lock_irq(&sem->wait_lock);

	/*
	* Try to reverse the lock attempt but if the count has changed
	* so that reversing fails, check if there are are no waiters,
	* and early-out if not
	*/
	do {
	if (atomic_long_try_cmpxchg(&sem->count, &count, count + adjust)) {
	count += adjust;
	break;
	}
	if (count > 0) {
	raw_spin_unlock_irq(&sem->wait_lock);
	return sem;
	}
	} while (1);

	list_add_tail(&waiter.list, &sem->read_wait);
	sem->wait_readers++;

	waiter.task = current;
	get_task_struct(current);

	/* if there are no active locks, wake the new lock owner(s) */
	if ((count & LDSEM_ACTIVE_MASK) == 0)
	__ldsem_wake(sem);

	raw_spin_unlock_irq(&sem->wait_lock);

	/* wait to be given the lock */
	for (;;) {
	set_current_state(TASK_UNINTERRUPTIBLE);

	if (!smp_load_acquire(&waiter.task))
	break;
	if (!timeout)
	break;
	timeout = schedule_timeout(timeout);
	}

	__set_current_state(TASK_RUNNING);

	if (!timeout) {
	/*
	* Lock timed out but check if this task was just
	* granted lock ownership - if so, pretend there
	* was no timeout; otherwise, cleanup lock wait.
	*/
	raw_spin_lock_irq(&sem->wait_lock);
	if (waiter.task) {
	atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count);
	sem->wait_readers--;
	list_del(&waiter.list);
	raw_spin_unlock_irq(&sem->wait_lock);
	put_task_struct(waiter.task);
	return NULL;
	}
	raw_spin_unlock_irq(&sem->wait_lock);
	}

	return sem;
	}

	/*
	* wait for the write lock to be granted
	*/
	static struct ld_semaphore __sched *
	down_write_failed(struct ld_semaphore *sem, long count, long timeout)
	{
	struct ldsem_waiter waiter;
	long adjust = -LDSEM_ACTIVE_BIAS;
	int locked = 0;

	/* set up my own style of waitqueue */
	raw_spin_lock_irq(&sem->wait_lock);

	/*
	* Try to reverse the lock attempt but if the count has changed
	* so that reversing fails, check if the lock is now owned,
	* and early-out if so.
	*/
	do {
	if (atomic_long_try_cmpxchg(&sem->count, &count, count + adjust))
	break;
	if ((count & LDSEM_ACTIVE_MASK) == LDSEM_ACTIVE_BIAS) {
	raw_spin_unlock_irq(&sem->wait_lock);
	return sem;
	}
	} while (1);

	list_add_tail(&waiter.list, &sem->write_wait);

	waiter.task = current;

	set_current_state(TASK_UNINTERRUPTIBLE);
	for (;;) {
	if (!timeout)
	break;
	raw_spin_unlock_irq(&sem->wait_lock);
	timeout = schedule_timeout(timeout);
	raw_spin_lock_irq(&sem->wait_lock);
	set_current_state(TASK_UNINTERRUPTIBLE);
	locked = writer_trylock(sem);
	if (locked)
	break;
	}

	if (!locked)
	atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count);
	list_del(&waiter.list);

	/*
	* In case of timeout, wake up every reader who gave the right of way
	* to writer. Prevent separation readers into two groups:
	* one that helds semaphore and another that sleeps.
	* (in case of no contention with a writer)
	*/
	if (!locked && list_empty(&sem->write_wait))
	__ldsem_wake_readers(sem);

	raw_spin_unlock_irq(&sem->wait_lock);

	__set_current_state(TASK_RUNNING);

	/* lock wait may have timed out */
	if (!locked)
	return NULL;
	return sem;
	}



	static int __ldsem_down_read_nested(struct ld_semaphore *sem,
	int subclass, long timeout)
	{
	long count;

	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);

	count = atomic_long_add_return(LDSEM_READ_BIAS, &sem->count);
	if (count <= 0) {
	lock_contended(&sem->dep_map, _RET_IP_);
	if (!down_read_failed(sem, count, timeout)) {
	rwsem_release(&sem->dep_map, 1, _RET_IP_);
	return 0;
	}
	}
	lock_acquired(&sem->dep_map, _RET_IP_);
	return 1;
	}

	static int __ldsem_down_write_nested(struct ld_semaphore *sem,
	int subclass, long timeout)
	{
	long count;

	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);

	count = atomic_long_add_return(LDSEM_WRITE_BIAS, &sem->count);
	if ((count & LDSEM_ACTIVE_MASK) != LDSEM_ACTIVE_BIAS) {
	lock_contended(&sem->dep_map, _RET_IP_);
	if (!down_write_failed(sem, count, timeout)) {
	rwsem_release(&sem->dep_map, 1, _RET_IP_);
	return 0;
	}
	}
	lock_acquired(&sem->dep_map, _RET_IP_);
	return 1;
	}


	/*
	* lock for reading -- returns 1 if successful, 0 if timed out
	*/
	int __sched ldsem_down_read(struct ld_semaphore *sem, long timeout)
	{
	might_sleep();
	return __ldsem_down_read_nested(sem, 0, timeout);
	}

	/*
	* trylock for reading -- returns 1 if successful, 0 if contention
	*/
	int ldsem_down_read_trylock(struct ld_semaphore *sem)
	{
	long count = atomic_long_read(&sem->count);

	while (count >= 0) {
	if (atomic_long_try_cmpxchg(&sem->count, &count, count + LDSEM_READ_BIAS)) {
	rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
	lock_acquired(&sem->dep_map, _RET_IP_);
	return 1;
	}
	}
	return 0;
	}

	/*
	* lock for writing -- returns 1 if successful, 0 if timed out
	*/
	int __sched ldsem_down_write(struct ld_semaphore *sem, long timeout)
	{
	might_sleep();
	return __ldsem_down_write_nested(sem, 0, timeout);
	}

	/*
	* trylock for writing -- returns 1 if successful, 0 if contention
	*/
	int ldsem_down_write_trylock(struct ld_semaphore *sem)
	{
	long count = atomic_long_read(&sem->count);

	while ((count & LDSEM_ACTIVE_MASK) == 0) {
	if (atomic_long_try_cmpxchg(&sem->count, &count, count + LDSEM_WRITE_BIAS)) {
	rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
	lock_acquired(&sem->dep_map, _RET_IP_);
	return 1;
	}
	}
	return 0;
	}

	/*
	* release a read lock
	*/
	void ldsem_up_read(struct ld_semaphore *sem)
	{
	long count;

	rwsem_release(&sem->dep_map, 1, _RET_IP_);

	count = atomic_long_add_return(-LDSEM_READ_BIAS, &sem->count);
	if (count < 0 && (count & LDSEM_ACTIVE_MASK) == 0)
	ldsem_wake(sem);
	}

	/*
	* release a write lock
	*/
	void ldsem_up_write(struct ld_semaphore *sem)
	{
	long count;

	rwsem_release(&sem->dep_map, 1, _RET_IP_);

	count = atomic_long_add_return(-LDSEM_WRITE_BIAS, &sem->count);
	if (count < 0)
	ldsem_wake(sem);
	}


	#ifdef CONFIG_DEBUG_LOCK_ALLOC

	int ldsem_down_read_nested(struct ld_semaphore *sem, int subclass, long timeout)
	{
	might_sleep();
	return __ldsem_down_read_nested(sem, subclass, timeout);
	}

	int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
	long timeout)
	{
	might_sleep();
	return __ldsem_down_write_nested(sem, subclass, timeout);
	}

	#endif