[linux-2.6-block.git] / drivers / tty / tty_ldsem.c

// 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>


#ifdef CONFIG_DEBUG_LOCK_ALLOC
# define __acq(l, s, t, r, c, n, i)		\
				lock_acquire(&(l)->dep_map, s, t, r, c, n, i)
# define __rel(l, n, i)				\
				lock_release(&(l)->dep_map, n, i)
#define lockdep_acquire(l, s, t, i)		__acq(l, s, t, 0, 1, NULL, i)
#define lockdep_acquire_nest(l, s, t, n, i)	__acq(l, s, t, 0, 1, n, i)
#define lockdep_acquire_read(l, s, t, i)	__acq(l, s, t, 1, 1, NULL, i)
#define lockdep_release(l, n, i)		__rel(l, n, i)
#else
# define lockdep_acquire(l, s, t, i)		do { } while (0)
# define lockdep_acquire_nest(l, s, t, n, i)	do { } while (0)
# define lockdep_acquire_read(l, s, t, i)	do { } while (0)
# define lockdep_release(l, n, i)		do { } while (0)
#endif

#ifdef CONFIG_LOCK_STAT
# define lock_stat(_lock, stat)		lock_##stat(&(_lock)->dep_map, _RET_IP_)
#else
# define lock_stat(_lock, stat)		do { } while (0)
#endif


#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_mb();
		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 (!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);
			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);
	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;

	lockdep_acquire_read(sem, subclass, 0, _RET_IP_);

	count = atomic_long_add_return(LDSEM_READ_BIAS, &sem->count);
	if (count <= 0) {
		lock_stat(sem, contended);
		if (!down_read_failed(sem, count, timeout)) {
			lockdep_release(sem, 1, _RET_IP_);
			return 0;
		}
	}
	lock_stat(sem, acquired);
	return 1;
}

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

	lockdep_acquire(sem, subclass, 0, _RET_IP_);

	count = atomic_long_add_return(LDSEM_WRITE_BIAS, &sem->count);
	if ((count & LDSEM_ACTIVE_MASK) != LDSEM_ACTIVE_BIAS) {
		lock_stat(sem, contended);
		if (!down_write_failed(sem, count, timeout)) {
			lockdep_release(sem, 1, _RET_IP_);
			return 0;
		}
	}
	lock_stat(sem, acquired);
	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)) {
			lockdep_acquire_read(sem, 0, 1, _RET_IP_);
			lock_stat(sem, acquired);
			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)) {
			lockdep_acquire(sem, 0, 1, _RET_IP_);
			lock_stat(sem, acquired);
			return 1;
		}
	}
	return 0;
}

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

	lockdep_release(sem, 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;

	lockdep_release(sem, 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
Commit	Line	Data
e3b3d0f5	1	// SPDX-License-Identifier: GPL-2.0
4898e640 PH	2	/*
	3	* Ldisc rw semaphore
	4	*
	5	* The ldisc semaphore is semantically a rw_semaphore but which enforces
	6	* an alternate policy, namely:
	7	* 1) Supports lock wait timeouts
	8	* 2) Write waiter has priority
	9	* 3) Downgrading is not supported
	10	*
	11	* Implementation notes:
	12	* 1) Upper half of semaphore count is a wait count (differs from rwsem
	13	* in that rwsem normalizes the upper half to the wait bias)
	14	* 2) Lacks overflow checking
	15	*
	16	* The generic counting was copied and modified from include/asm-generic/rwsem.h
	17	* by Paul Mackerras <paulus@samba.org>.
	18	*
	19	* The scheduling policy was copied and modified from lib/rwsem.c
	20	* Written by David Howells (dhowells@redhat.com).
	21	*
	22	* This implementation incorporates the write lock stealing work of
	23	* Michel Lespinasse <walken@google.com>.
	24	*
	25	* Copyright (C) 2013 Peter Hurley <peter@hurleysoftware.com>
4898e640 PH	26	*/
	27
	28	#include <linux/list.h>
	29	#include <linux/spinlock.h>
	30	#include <linux/atomic.h>
	31	#include <linux/tty.h>
	32	#include <linux/sched.h>
b17b0153	33	#include <linux/sched/debug.h>
0881e7bd	34	#include <linux/sched/task.h>
4898e640 PH	35
	36
	37	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	38	# define __acq(l, s, t, r, c, n, i) \
	39	lock_acquire(&(l)->dep_map, s, t, r, c, n, i)
	40	# define __rel(l, n, i) \
	41	lock_release(&(l)->dep_map, n, i)
fb9edbe9 ON	42	#define lockdep_acquire(l, s, t, i) __acq(l, s, t, 0, 1, NULL, i)
	43	#define lockdep_acquire_nest(l, s, t, n, i) __acq(l, s, t, 0, 1, n, i)
	44	#define lockdep_acquire_read(l, s, t, i) __acq(l, s, t, 1, 1, NULL, i)
	45	#define lockdep_release(l, n, i) __rel(l, n, i)
4898e640 PH	46	#else
	47	# define lockdep_acquire(l, s, t, i) do { } while (0)
	48	# define lockdep_acquire_nest(l, s, t, n, i) do { } while (0)
	49	# define lockdep_acquire_read(l, s, t, i) do { } while (0)
	50	# define lockdep_release(l, n, i) do { } while (0)
	51	#endif
	52
	53	#ifdef CONFIG_LOCK_STAT
	54	# define lock_stat(_lock, stat) lock_##stat(&(_lock)->dep_map, _RET_IP_)
	55	#else
	56	# define lock_stat(_lock, stat) do { } while (0)
	57	#endif
	58
	59
	60	#if BITS_PER_LONG == 64
	61	# define LDSEM_ACTIVE_MASK 0xffffffffL
	62	#else
	63	# define LDSEM_ACTIVE_MASK 0x0000ffffL
	64	#endif
	65
	66	#define LDSEM_UNLOCKED 0L
	67	#define LDSEM_ACTIVE_BIAS 1L
	68	#define LDSEM_WAIT_BIAS (-LDSEM_ACTIVE_MASK-1)
	69	#define LDSEM_READ_BIAS LDSEM_ACTIVE_BIAS
	70	#define LDSEM_WRITE_BIAS (LDSEM_WAIT_BIAS + LDSEM_ACTIVE_BIAS)
	71
	72	struct ldsem_waiter {
	73	struct list_head list;
	74	struct task_struct *task;
	75	};
	76
4898e640 PH	77	/*
	78	* Initialize an ldsem:
	79	*/
	80	void __init_ldsem(struct ld_semaphore sem, const char name,
	81	struct lock_class_key *key)
	82	{
	83	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	84	/*
	85	* Make sure we are not reinitializing a held semaphore:
	86	*/
	87	debug_check_no_locks_freed((void )sem, sizeof(sem));
	88	lockdep_init_map(&sem->dep_map, name, key, 0);
	89	#endif
5fd691af	90	atomic_long_set(&sem->count, LDSEM_UNLOCKED);
4898e640 PH	91	sem->wait_readers = 0;
	92	raw_spin_lock_init(&sem->wait_lock);
	93	INIT_LIST_HEAD(&sem->read_wait);
	94	INIT_LIST_HEAD(&sem->write_wait);
	95	}
	96
	97	static void __ldsem_wake_readers(struct ld_semaphore *sem)
	98	{
	99	struct ldsem_waiter waiter, next;
	100	struct task_struct *tsk;
	101	long adjust, count;
	102
5fd691af PZ	103	/*
5fd691af PZ	104	* Try to grant read locks to all readers on the read wait list.
4898e640 PH	105	* Note the 'active part' of the count is incremented by
	106	* the number of readers before waking any processes up.
	107	*/
	108	adjust = sem->wait_readers * (LDSEM_ACTIVE_BIAS - LDSEM_WAIT_BIAS);
5fd691af	109	count = atomic_long_add_return(adjust, &sem->count);
4898e640 PH	110	do {
	111	if (count > 0)
	112	break;
5fd691af	113	if (atomic_long_try_cmpxchg(&sem->count, &count, count - adjust))
4898e640 PH	114	return;
	115	} while (1);
	116
	117	list_for_each_entry_safe(waiter, next, &sem->read_wait, list) {
	118	tsk = waiter->task;
	119	smp_mb();
	120	waiter->task = NULL;
	121	wake_up_process(tsk);
	122	put_task_struct(tsk);
	123	}
	124	INIT_LIST_HEAD(&sem->read_wait);
	125	sem->wait_readers = 0;
	126	}
	127
	128	static inline int writer_trylock(struct ld_semaphore *sem)
	129	{
5fd691af PZ	130	/*
5fd691af PZ	131	* Only wake this writer if the active part of the count can be
4898e640 PH	132	* transitioned from 0 -> 1
4898e640 PH	133	*/
5fd691af	134	long count = atomic_long_add_return(LDSEM_ACTIVE_BIAS, &sem->count);
4898e640 PH	135	do {
	136	if ((count & LDSEM_ACTIVE_MASK) == LDSEM_ACTIVE_BIAS)
	137	return 1;
5fd691af	138	if (atomic_long_try_cmpxchg(&sem->count, &count, count - LDSEM_ACTIVE_BIAS))
4898e640 PH	139	return 0;
	140	} while (1);
	141	}
	142
	143	static void __ldsem_wake_writer(struct ld_semaphore *sem)
	144	{
	145	struct ldsem_waiter *waiter;
	146
	147	waiter = list_entry(sem->write_wait.next, struct ldsem_waiter, list);
	148	wake_up_process(waiter->task);
	149	}
	150
	151	/*
	152	* handle the lock release when processes blocked on it that can now run
	153	* - if we come here from up_xxxx(), then:
	154	* - the 'active part' of count (&0x0000ffff) reached 0 (but may have changed)
	155	* - the 'waiting part' of count (&0xffff0000) is -ve (and will still be so)
	156	* - the spinlock must be held by the caller
	157	* - woken process blocks are discarded from the list after having task zeroed
	158	*/
	159	static void __ldsem_wake(struct ld_semaphore *sem)
	160	{
	161	if (!list_empty(&sem->write_wait))
	162	__ldsem_wake_writer(sem);
	163	else if (!list_empty(&sem->read_wait))
	164	__ldsem_wake_readers(sem);
	165	}
	166
	167	static void ldsem_wake(struct ld_semaphore *sem)
	168	{
	169	unsigned long flags;
	170
	171	raw_spin_lock_irqsave(&sem->wait_lock, flags);
	172	__ldsem_wake(sem);
	173	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
	174	}
	175
	176	/*
	177	* wait for the read lock to be granted
	178	*/
	179	static struct ld_semaphore __sched *
	180	down_read_failed(struct ld_semaphore *sem, long count, long timeout)
	181	{
	182	struct ldsem_waiter waiter;
4898e640 PH	183	long adjust = -LDSEM_ACTIVE_BIAS + LDSEM_WAIT_BIAS;
	184
	185	/* set up my own style of waitqueue */
	186	raw_spin_lock_irq(&sem->wait_lock);
	187
5fd691af PZ	188	/*
5fd691af PZ	189	* Try to reverse the lock attempt but if the count has changed
4898e640	190	* so that reversing fails, check if there are are no waiters,
5fd691af PZ	191	* and early-out if not
5fd691af PZ	192	*/
4898e640	193	do {
5fd691af PZ	194	if (atomic_long_try_cmpxchg(&sem->count, &count, count + adjust)) {
5fd691af PZ	195	count += adjust;
4898e640	196	break;
5fd691af	197	}
4898e640 PH	198	if (count > 0) {
	199	raw_spin_unlock_irq(&sem->wait_lock);
	200	return sem;
	201	}
	202	} while (1);
	203
	204	list_add_tail(&waiter.list, &sem->read_wait);
	205	sem->wait_readers++;
	206
5376f2e7 DB	207	waiter.task = current;
5376f2e7 DB	208	get_task_struct(current);
4898e640 PH	209
	210	/* if there are no active locks, wake the new lock owner(s) */
	211	if ((count & LDSEM_ACTIVE_MASK) == 0)
	212	__ldsem_wake(sem);
	213
	214	raw_spin_unlock_irq(&sem->wait_lock);
	215
	216	/* wait to be given the lock */
	217	for (;;) {
642fa448	218	set_current_state(TASK_UNINTERRUPTIBLE);
4898e640 PH	219
	220	if (!waiter.task)
	221	break;
	222	if (!timeout)
	223	break;
	224	timeout = schedule_timeout(timeout);
	225	}
	226
642fa448	227	__set_current_state(TASK_RUNNING);
4898e640 PH	228
4898e640 PH	229	if (!timeout) {
5fd691af PZ	230	/*
5fd691af PZ	231	* Lock timed out but check if this task was just
4898e640	232	* granted lock ownership - if so, pretend there
5fd691af PZ	233	* was no timeout; otherwise, cleanup lock wait.
5fd691af PZ	234	*/
4898e640 PH	235	raw_spin_lock_irq(&sem->wait_lock);
4898e640 PH	236	if (waiter.task) {
5fd691af	237	atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count);
4898e640 PH	238	list_del(&waiter.list);
	239	raw_spin_unlock_irq(&sem->wait_lock);
	240	put_task_struct(waiter.task);
	241	return NULL;
	242	}
	243	raw_spin_unlock_irq(&sem->wait_lock);
	244	}
	245
	246	return sem;
	247	}
	248
	249	/*
	250	* wait for the write lock to be granted
	251	*/
	252	static struct ld_semaphore __sched *
	253	down_write_failed(struct ld_semaphore *sem, long count, long timeout)
	254	{
	255	struct ldsem_waiter waiter;
4898e640 PH	256	long adjust = -LDSEM_ACTIVE_BIAS;
	257	int locked = 0;
	258
	259	/* set up my own style of waitqueue */
	260	raw_spin_lock_irq(&sem->wait_lock);
	261
5fd691af PZ	262	/*
5fd691af PZ	263	* Try to reverse the lock attempt but if the count has changed
4898e640	264	* so that reversing fails, check if the lock is now owned,
5fd691af PZ	265	* and early-out if so.
5fd691af PZ	266	*/
4898e640	267	do {
5fd691af	268	if (atomic_long_try_cmpxchg(&sem->count, &count, count + adjust))
4898e640 PH	269	break;
	270	if ((count & LDSEM_ACTIVE_MASK) == LDSEM_ACTIVE_BIAS) {
	271	raw_spin_unlock_irq(&sem->wait_lock);
	272	return sem;
	273	}
	274	} while (1);
	275
	276	list_add_tail(&waiter.list, &sem->write_wait);
	277
5376f2e7	278	waiter.task = current;
4898e640	279
642fa448	280	set_current_state(TASK_UNINTERRUPTIBLE);
4898e640 PH	281	for (;;) {
	282	if (!timeout)
	283	break;
	284	raw_spin_unlock_irq(&sem->wait_lock);
	285	timeout = schedule_timeout(timeout);
	286	raw_spin_lock_irq(&sem->wait_lock);
642fa448	287	set_current_state(TASK_UNINTERRUPTIBLE);
f9ce5ccf GKH	288	locked = writer_trylock(sem);
f9ce5ccf GKH	289	if (locked)
4898e640 PH	290	break;
	291	}
	292
	293	if (!locked)
5fd691af	294	atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count);
4898e640 PH	295	list_del(&waiter.list);
	296	raw_spin_unlock_irq(&sem->wait_lock);
	297
642fa448	298	__set_current_state(TASK_RUNNING);
4898e640 PH	299
	300	/* lock wait may have timed out */
	301	if (!locked)
	302	return NULL;
	303	return sem;
	304	}
	305
	306
	307
fc0285f2	308	static int __ldsem_down_read_nested(struct ld_semaphore *sem,
4898e640 PH	309	int subclass, long timeout)
	310	{
	311	long count;
	312
	313	lockdep_acquire_read(sem, subclass, 0, _RET_IP_);
	314
5fd691af	315	count = atomic_long_add_return(LDSEM_READ_BIAS, &sem->count);
4898e640 PH	316	if (count <= 0) {
	317	lock_stat(sem, contended);
	318	if (!down_read_failed(sem, count, timeout)) {
	319	lockdep_release(sem, 1, _RET_IP_);
	320	return 0;
	321	}
	322	}
	323	lock_stat(sem, acquired);
	324	return 1;
	325	}
	326
5ef6504e	327	static int __ldsem_down_write_nested(struct ld_semaphore *sem,
4898e640 PH	328	int subclass, long timeout)
	329	{
	330	long count;
	331
	332	lockdep_acquire(sem, subclass, 0, _RET_IP_);
	333
5fd691af	334	count = atomic_long_add_return(LDSEM_WRITE_BIAS, &sem->count);
4898e640 PH	335	if ((count & LDSEM_ACTIVE_MASK) != LDSEM_ACTIVE_BIAS) {
	336	lock_stat(sem, contended);
	337	if (!down_write_failed(sem, count, timeout)) {
	338	lockdep_release(sem, 1, _RET_IP_);
	339	return 0;
	340	}
	341	}
	342	lock_stat(sem, acquired);
	343	return 1;
	344	}
	345
	346
	347	/*
	348	* lock for reading -- returns 1 if successful, 0 if timed out
	349	*/
	350	int __sched ldsem_down_read(struct ld_semaphore *sem, long timeout)
	351	{
	352	might_sleep();
	353	return __ldsem_down_read_nested(sem, 0, timeout);
	354	}
	355
	356	/*
	357	* trylock for reading -- returns 1 if successful, 0 if contention
	358	*/
	359	int ldsem_down_read_trylock(struct ld_semaphore *sem)
	360	{
5fd691af	361	long count = atomic_long_read(&sem->count);
4898e640 PH	362
4898e640 PH	363	while (count >= 0) {
5fd691af	364	if (atomic_long_try_cmpxchg(&sem->count, &count, count + LDSEM_READ_BIAS)) {
4898e640 PH	365	lockdep_acquire_read(sem, 0, 1, _RET_IP_);
	366	lock_stat(sem, acquired);
	367	return 1;
	368	}
	369	}
	370	return 0;
	371	}
	372
	373	/*
	374	* lock for writing -- returns 1 if successful, 0 if timed out
	375	*/
	376	int __sched ldsem_down_write(struct ld_semaphore *sem, long timeout)
	377	{
	378	might_sleep();
	379	return __ldsem_down_write_nested(sem, 0, timeout);
	380	}
	381
	382	/*
	383	* trylock for writing -- returns 1 if successful, 0 if contention
	384	*/
	385	int ldsem_down_write_trylock(struct ld_semaphore *sem)
	386	{
5fd691af	387	long count = atomic_long_read(&sem->count);
4898e640 PH	388
4898e640 PH	389	while ((count & LDSEM_ACTIVE_MASK) == 0) {
5fd691af	390	if (atomic_long_try_cmpxchg(&sem->count, &count, count + LDSEM_WRITE_BIAS)) {
4898e640 PH	391	lockdep_acquire(sem, 0, 1, _RET_IP_);
	392	lock_stat(sem, acquired);
	393	return 1;
	394	}
	395	}
	396	return 0;
	397	}
	398
	399	/*
	400	* release a read lock
	401	*/
	402	void ldsem_up_read(struct ld_semaphore *sem)
	403	{
	404	long count;
	405
	406	lockdep_release(sem, 1, _RET_IP_);
	407
5fd691af	408	count = atomic_long_add_return(-LDSEM_READ_BIAS, &sem->count);
4898e640 PH	409	if (count < 0 && (count & LDSEM_ACTIVE_MASK) == 0)
	410	ldsem_wake(sem);
	411	}
	412
	413	/*
	414	* release a write lock
	415	*/
	416	void ldsem_up_write(struct ld_semaphore *sem)
	417	{
	418	long count;
	419
	420	lockdep_release(sem, 1, _RET_IP_);
	421
5fd691af	422	count = atomic_long_add_return(-LDSEM_WRITE_BIAS, &sem->count);
4898e640 PH	423	if (count < 0)
	424	ldsem_wake(sem);
	425	}
	426
	427
	428	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	429
	430	int ldsem_down_read_nested(struct ld_semaphore *sem, int subclass, long timeout)
	431	{
	432	might_sleep();
	433	return __ldsem_down_read_nested(sem, subclass, timeout);
	434	}
	435
	436	int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
	437	long timeout)
	438	{
	439	might_sleep();
	440	return __ldsem_down_write_nested(sem, subclass, timeout);
	441	}
	442
	443	#endif