[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>


#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);
			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
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
4898e640 PH	36
4898e640 PH	37	#if BITS_PER_LONG == 64
	38	# define LDSEM_ACTIVE_MASK 0xffffffffL
	39	#else
	40	# define LDSEM_ACTIVE_MASK 0x0000ffffL
	41	#endif
	42
	43	#define LDSEM_UNLOCKED 0L
	44	#define LDSEM_ACTIVE_BIAS 1L
	45	#define LDSEM_WAIT_BIAS (-LDSEM_ACTIVE_MASK-1)
	46	#define LDSEM_READ_BIAS LDSEM_ACTIVE_BIAS
	47	#define LDSEM_WRITE_BIAS (LDSEM_WAIT_BIAS + LDSEM_ACTIVE_BIAS)
	48
	49	struct ldsem_waiter {
	50	struct list_head list;
	51	struct task_struct *task;
	52	};
	53
4898e640 PH	54	/*
	55	* Initialize an ldsem:
	56	*/
	57	void __init_ldsem(struct ld_semaphore sem, const char name,
	58	struct lock_class_key *key)
	59	{
	60	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	61	/*
	62	* Make sure we are not reinitializing a held semaphore:
	63	*/
	64	debug_check_no_locks_freed((void )sem, sizeof(sem));
	65	lockdep_init_map(&sem->dep_map, name, key, 0);
	66	#endif
5fd691af	67	atomic_long_set(&sem->count, LDSEM_UNLOCKED);
4898e640 PH	68	sem->wait_readers = 0;
	69	raw_spin_lock_init(&sem->wait_lock);
	70	INIT_LIST_HEAD(&sem->read_wait);
	71	INIT_LIST_HEAD(&sem->write_wait);
	72	}
	73
	74	static void __ldsem_wake_readers(struct ld_semaphore *sem)
	75	{
	76	struct ldsem_waiter waiter, next;
	77	struct task_struct *tsk;
	78	long adjust, count;
	79
5fd691af PZ	80	/*
5fd691af PZ	81	* Try to grant read locks to all readers on the read wait list.
4898e640 PH	82	* Note the 'active part' of the count is incremented by
	83	* the number of readers before waking any processes up.
	84	*/
	85	adjust = sem->wait_readers * (LDSEM_ACTIVE_BIAS - LDSEM_WAIT_BIAS);
5fd691af	86	count = atomic_long_add_return(adjust, &sem->count);
4898e640 PH	87	do {
	88	if (count > 0)
	89	break;
5fd691af	90	if (atomic_long_try_cmpxchg(&sem->count, &count, count - adjust))
4898e640 PH	91	return;
	92	} while (1);
	93
	94	list_for_each_entry_safe(waiter, next, &sem->read_wait, list) {
	95	tsk = waiter->task;
	96	smp_mb();
	97	waiter->task = NULL;
	98	wake_up_process(tsk);
	99	put_task_struct(tsk);
	100	}
	101	INIT_LIST_HEAD(&sem->read_wait);
	102	sem->wait_readers = 0;
	103	}
	104
	105	static inline int writer_trylock(struct ld_semaphore *sem)
	106	{
5fd691af PZ	107	/*
5fd691af PZ	108	* Only wake this writer if the active part of the count can be
4898e640 PH	109	* transitioned from 0 -> 1
4898e640 PH	110	*/
5fd691af	111	long count = atomic_long_add_return(LDSEM_ACTIVE_BIAS, &sem->count);
4898e640 PH	112	do {
	113	if ((count & LDSEM_ACTIVE_MASK) == LDSEM_ACTIVE_BIAS)
	114	return 1;
5fd691af	115	if (atomic_long_try_cmpxchg(&sem->count, &count, count - LDSEM_ACTIVE_BIAS))
4898e640 PH	116	return 0;
	117	} while (1);
	118	}
	119
	120	static void __ldsem_wake_writer(struct ld_semaphore *sem)
	121	{
	122	struct ldsem_waiter *waiter;
	123
	124	waiter = list_entry(sem->write_wait.next, struct ldsem_waiter, list);
	125	wake_up_process(waiter->task);
	126	}
	127
	128	/*
	129	* handle the lock release when processes blocked on it that can now run
	130	* - if we come here from up_xxxx(), then:
	131	* - the 'active part' of count (&0x0000ffff) reached 0 (but may have changed)
	132	* - the 'waiting part' of count (&0xffff0000) is -ve (and will still be so)
	133	* - the spinlock must be held by the caller
	134	* - woken process blocks are discarded from the list after having task zeroed
	135	*/
	136	static void __ldsem_wake(struct ld_semaphore *sem)
	137	{
	138	if (!list_empty(&sem->write_wait))
	139	__ldsem_wake_writer(sem);
	140	else if (!list_empty(&sem->read_wait))
	141	__ldsem_wake_readers(sem);
	142	}
	143
	144	static void ldsem_wake(struct ld_semaphore *sem)
	145	{
	146	unsigned long flags;
	147
	148	raw_spin_lock_irqsave(&sem->wait_lock, flags);
	149	__ldsem_wake(sem);
	150	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
	151	}
	152
	153	/*
	154	* wait for the read lock to be granted
	155	*/
	156	static struct ld_semaphore __sched *
	157	down_read_failed(struct ld_semaphore *sem, long count, long timeout)
	158	{
	159	struct ldsem_waiter waiter;
4898e640 PH	160	long adjust = -LDSEM_ACTIVE_BIAS + LDSEM_WAIT_BIAS;
	161
	162	/* set up my own style of waitqueue */
	163	raw_spin_lock_irq(&sem->wait_lock);
	164
5fd691af PZ	165	/*
5fd691af PZ	166	* Try to reverse the lock attempt but if the count has changed
4898e640	167	* so that reversing fails, check if there are are no waiters,
5fd691af PZ	168	* and early-out if not
5fd691af PZ	169	*/
4898e640	170	do {
5fd691af PZ	171	if (atomic_long_try_cmpxchg(&sem->count, &count, count + adjust)) {
5fd691af PZ	172	count += adjust;
4898e640	173	break;
5fd691af	174	}
4898e640 PH	175	if (count > 0) {
	176	raw_spin_unlock_irq(&sem->wait_lock);
	177	return sem;
	178	}
	179	} while (1);
	180
	181	list_add_tail(&waiter.list, &sem->read_wait);
	182	sem->wait_readers++;
	183
5376f2e7 DB	184	waiter.task = current;
5376f2e7 DB	185	get_task_struct(current);
4898e640 PH	186
	187	/* if there are no active locks, wake the new lock owner(s) */
	188	if ((count & LDSEM_ACTIVE_MASK) == 0)
	189	__ldsem_wake(sem);
	190
	191	raw_spin_unlock_irq(&sem->wait_lock);
	192
	193	/* wait to be given the lock */
	194	for (;;) {
642fa448	195	set_current_state(TASK_UNINTERRUPTIBLE);
4898e640 PH	196
	197	if (!waiter.task)
	198	break;
	199	if (!timeout)
	200	break;
	201	timeout = schedule_timeout(timeout);
	202	}
	203
642fa448	204	__set_current_state(TASK_RUNNING);
4898e640 PH	205
4898e640 PH	206	if (!timeout) {
5fd691af PZ	207	/*
5fd691af PZ	208	* Lock timed out but check if this task was just
4898e640	209	* granted lock ownership - if so, pretend there
5fd691af PZ	210	* was no timeout; otherwise, cleanup lock wait.
5fd691af PZ	211	*/
4898e640 PH	212	raw_spin_lock_irq(&sem->wait_lock);
4898e640 PH	213	if (waiter.task) {
5fd691af	214	atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count);
2f588cee	215	sem->wait_readers--;
4898e640 PH	216	list_del(&waiter.list);
	217	raw_spin_unlock_irq(&sem->wait_lock);
	218	put_task_struct(waiter.task);
	219	return NULL;
	220	}
	221	raw_spin_unlock_irq(&sem->wait_lock);
	222	}
	223
	224	return sem;
	225	}
	226
	227	/*
	228	* wait for the write lock to be granted
	229	*/
	230	static struct ld_semaphore __sched *
	231	down_write_failed(struct ld_semaphore *sem, long count, long timeout)
	232	{
	233	struct ldsem_waiter waiter;
4898e640 PH	234	long adjust = -LDSEM_ACTIVE_BIAS;
	235	int locked = 0;
	236
	237	/* set up my own style of waitqueue */
	238	raw_spin_lock_irq(&sem->wait_lock);
	239
5fd691af PZ	240	/*
5fd691af PZ	241	* Try to reverse the lock attempt but if the count has changed
4898e640	242	* so that reversing fails, check if the lock is now owned,
5fd691af PZ	243	* and early-out if so.
5fd691af PZ	244	*/
4898e640	245	do {
5fd691af	246	if (atomic_long_try_cmpxchg(&sem->count, &count, count + adjust))
4898e640 PH	247	break;
	248	if ((count & LDSEM_ACTIVE_MASK) == LDSEM_ACTIVE_BIAS) {
	249	raw_spin_unlock_irq(&sem->wait_lock);
	250	return sem;
	251	}
	252	} while (1);
	253
	254	list_add_tail(&waiter.list, &sem->write_wait);
	255
5376f2e7	256	waiter.task = current;
4898e640	257
642fa448	258	set_current_state(TASK_UNINTERRUPTIBLE);
4898e640 PH	259	for (;;) {
	260	if (!timeout)
	261	break;
	262	raw_spin_unlock_irq(&sem->wait_lock);
	263	timeout = schedule_timeout(timeout);
	264	raw_spin_lock_irq(&sem->wait_lock);
642fa448	265	set_current_state(TASK_UNINTERRUPTIBLE);
f9ce5ccf GKH	266	locked = writer_trylock(sem);
f9ce5ccf GKH	267	if (locked)
4898e640 PH	268	break;
	269	}
	270
	271	if (!locked)
5fd691af	272	atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count);
4898e640	273	list_del(&waiter.list);
231f8fd0 DS	274
	275	/*
	276	* In case of timeout, wake up every reader who gave the right of way
	277	* to writer. Prevent separation readers into two groups:
	278	* one that helds semaphore and another that sleeps.
	279	* (in case of no contention with a writer)
	280	*/
	281	if (!locked && list_empty(&sem->write_wait))
	282	__ldsem_wake_readers(sem);
	283
4898e640 PH	284	raw_spin_unlock_irq(&sem->wait_lock);
4898e640 PH	285
642fa448	286	__set_current_state(TASK_RUNNING);
4898e640 PH	287
	288	/* lock wait may have timed out */
	289	if (!locked)
	290	return NULL;
	291	return sem;
	292	}
	293
	294
	295
fc0285f2	296	static int __ldsem_down_read_nested(struct ld_semaphore *sem,
4898e640 PH	297	int subclass, long timeout)
	298	{
	299	long count;
	300
c18ad0cf	301	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
4898e640	302
5fd691af	303	count = atomic_long_add_return(LDSEM_READ_BIAS, &sem->count);
4898e640	304	if (count <= 0) {
c18ad0cf	305	lock_contended(&sem->dep_map, _RET_IP_);
4898e640	306	if (!down_read_failed(sem, count, timeout)) {
c18ad0cf	307	rwsem_release(&sem->dep_map, 1, _RET_IP_);
4898e640 PH	308	return 0;
	309	}
	310	}
c18ad0cf	311	lock_acquired(&sem->dep_map, _RET_IP_);
4898e640 PH	312	return 1;
	313	}
	314
5ef6504e	315	static int __ldsem_down_write_nested(struct ld_semaphore *sem,
4898e640 PH	316	int subclass, long timeout)
	317	{
	318	long count;
	319
c18ad0cf	320	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
4898e640	321
5fd691af	322	count = atomic_long_add_return(LDSEM_WRITE_BIAS, &sem->count);
4898e640	323	if ((count & LDSEM_ACTIVE_MASK) != LDSEM_ACTIVE_BIAS) {
c18ad0cf	324	lock_contended(&sem->dep_map, _RET_IP_);
4898e640	325	if (!down_write_failed(sem, count, timeout)) {
c18ad0cf	326	rwsem_release(&sem->dep_map, 1, _RET_IP_);
4898e640 PH	327	return 0;
	328	}
	329	}
c18ad0cf	330	lock_acquired(&sem->dep_map, _RET_IP_);
4898e640 PH	331	return 1;
	332	}
	333
	334
	335	/*
	336	* lock for reading -- returns 1 if successful, 0 if timed out
	337	*/
	338	int __sched ldsem_down_read(struct ld_semaphore *sem, long timeout)
	339	{
	340	might_sleep();
	341	return __ldsem_down_read_nested(sem, 0, timeout);
	342	}
	343
	344	/*
	345	* trylock for reading -- returns 1 if successful, 0 if contention
	346	*/
	347	int ldsem_down_read_trylock(struct ld_semaphore *sem)
	348	{
5fd691af	349	long count = atomic_long_read(&sem->count);
4898e640 PH	350
4898e640 PH	351	while (count >= 0) {
5fd691af	352	if (atomic_long_try_cmpxchg(&sem->count, &count, count + LDSEM_READ_BIAS)) {
c18ad0cf PZ	353	rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
c18ad0cf PZ	354	lock_acquired(&sem->dep_map, _RET_IP_);
4898e640 PH	355	return 1;
	356	}
	357	}
	358	return 0;
	359	}
	360
	361	/*
	362	* lock for writing -- returns 1 if successful, 0 if timed out
	363	*/
	364	int __sched ldsem_down_write(struct ld_semaphore *sem, long timeout)
	365	{
	366	might_sleep();
	367	return __ldsem_down_write_nested(sem, 0, timeout);
	368	}
	369
	370	/*
	371	* trylock for writing -- returns 1 if successful, 0 if contention
	372	*/
	373	int ldsem_down_write_trylock(struct ld_semaphore *sem)
	374	{
5fd691af	375	long count = atomic_long_read(&sem->count);
4898e640 PH	376
4898e640 PH	377	while ((count & LDSEM_ACTIVE_MASK) == 0) {
5fd691af	378	if (atomic_long_try_cmpxchg(&sem->count, &count, count + LDSEM_WRITE_BIAS)) {
c18ad0cf PZ	379	rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
c18ad0cf PZ	380	lock_acquired(&sem->dep_map, _RET_IP_);
4898e640 PH	381	return 1;
	382	}
	383	}
	384	return 0;
	385	}
	386
	387	/*
	388	* release a read lock
	389	*/
	390	void ldsem_up_read(struct ld_semaphore *sem)
	391	{
	392	long count;
	393
c18ad0cf	394	rwsem_release(&sem->dep_map, 1, _RET_IP_);
4898e640	395
5fd691af	396	count = atomic_long_add_return(-LDSEM_READ_BIAS, &sem->count);
4898e640 PH	397	if (count < 0 && (count & LDSEM_ACTIVE_MASK) == 0)
	398	ldsem_wake(sem);
	399	}
	400
	401	/*
	402	* release a write lock
	403	*/
	404	void ldsem_up_write(struct ld_semaphore *sem)
	405	{
	406	long count;
	407
c18ad0cf	408	rwsem_release(&sem->dep_map, 1, _RET_IP_);
4898e640	409
5fd691af	410	count = atomic_long_add_return(-LDSEM_WRITE_BIAS, &sem->count);
4898e640 PH	411	if (count < 0)
	412	ldsem_wake(sem);
	413	}
	414
	415
	416	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	417
	418	int ldsem_down_read_nested(struct ld_semaphore *sem, int subclass, long timeout)
	419	{
	420	might_sleep();
	421	return __ldsem_down_read_nested(sem, subclass, timeout);
	422	}
	423
	424	int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
	425	long timeout)
	426	{
	427	might_sleep();
	428	return __ldsem_down_write_nested(sem, subclass, timeout);
	429	}
	430
	431	#endif