[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_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
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;
952041a8	96	smp_store_release(&waiter->task, NULL);
4898e640 PH	97	wake_up_process(tsk);
	98	put_task_struct(tsk);
	99	}
	100	INIT_LIST_HEAD(&sem->read_wait);
	101	sem->wait_readers = 0;
	102	}
	103
	104	static inline int writer_trylock(struct ld_semaphore *sem)
	105	{
5fd691af PZ	106	/*
5fd691af PZ	107	* Only wake this writer if the active part of the count can be
4898e640 PH	108	* transitioned from 0 -> 1
4898e640 PH	109	*/
5fd691af	110	long count = atomic_long_add_return(LDSEM_ACTIVE_BIAS, &sem->count);
4898e640 PH	111	do {
	112	if ((count & LDSEM_ACTIVE_MASK) == LDSEM_ACTIVE_BIAS)
	113	return 1;
5fd691af	114	if (atomic_long_try_cmpxchg(&sem->count, &count, count - LDSEM_ACTIVE_BIAS))
4898e640 PH	115	return 0;
	116	} while (1);
	117	}
	118
	119	static void __ldsem_wake_writer(struct ld_semaphore *sem)
	120	{
	121	struct ldsem_waiter *waiter;
	122
	123	waiter = list_entry(sem->write_wait.next, struct ldsem_waiter, list);
	124	wake_up_process(waiter->task);
	125	}
	126
	127	/*
	128	* handle the lock release when processes blocked on it that can now run
	129	* - if we come here from up_xxxx(), then:
	130	* - the 'active part' of count (&0x0000ffff) reached 0 (but may have changed)
	131	* - the 'waiting part' of count (&0xffff0000) is -ve (and will still be so)
	132	* - the spinlock must be held by the caller
	133	* - woken process blocks are discarded from the list after having task zeroed
	134	*/
	135	static void __ldsem_wake(struct ld_semaphore *sem)
	136	{
	137	if (!list_empty(&sem->write_wait))
	138	__ldsem_wake_writer(sem);
	139	else if (!list_empty(&sem->read_wait))
	140	__ldsem_wake_readers(sem);
	141	}
	142
	143	static void ldsem_wake(struct ld_semaphore *sem)
	144	{
	145	unsigned long flags;
	146
	147	raw_spin_lock_irqsave(&sem->wait_lock, flags);
	148	__ldsem_wake(sem);
	149	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
	150	}
	151
	152	/*
	153	* wait for the read lock to be granted
	154	*/
	155	static struct ld_semaphore __sched *
	156	down_read_failed(struct ld_semaphore *sem, long count, long timeout)
	157	{
	158	struct ldsem_waiter waiter;
4898e640 PH	159	long adjust = -LDSEM_ACTIVE_BIAS + LDSEM_WAIT_BIAS;
	160
	161	/* set up my own style of waitqueue */
	162	raw_spin_lock_irq(&sem->wait_lock);
	163
5fd691af PZ	164	/*
5fd691af PZ	165	* Try to reverse the lock attempt but if the count has changed
4898e640	166	* so that reversing fails, check if there are are no waiters,
5fd691af PZ	167	* and early-out if not
5fd691af PZ	168	*/
4898e640	169	do {
5fd691af PZ	170	if (atomic_long_try_cmpxchg(&sem->count, &count, count + adjust)) {
5fd691af PZ	171	count += adjust;
4898e640	172	break;
5fd691af	173	}
4898e640 PH	174	if (count > 0) {
	175	raw_spin_unlock_irq(&sem->wait_lock);
	176	return sem;
	177	}
	178	} while (1);
	179
	180	list_add_tail(&waiter.list, &sem->read_wait);
	181	sem->wait_readers++;
	182
5376f2e7 DB	183	waiter.task = current;
5376f2e7 DB	184	get_task_struct(current);
4898e640 PH	185
	186	/* if there are no active locks, wake the new lock owner(s) */
	187	if ((count & LDSEM_ACTIVE_MASK) == 0)
	188	__ldsem_wake(sem);
	189
	190	raw_spin_unlock_irq(&sem->wait_lock);
	191
	192	/* wait to be given the lock */
	193	for (;;) {
642fa448	194	set_current_state(TASK_UNINTERRUPTIBLE);
4898e640	195
952041a8	196	if (!smp_load_acquire(&waiter.task))
4898e640 PH	197	break;
	198	if (!timeout)
	199	break;
	200	timeout = schedule_timeout(timeout);
	201	}
	202
642fa448	203	__set_current_state(TASK_RUNNING);
4898e640 PH	204
4898e640 PH	205	if (!timeout) {
5fd691af PZ	206	/*
5fd691af PZ	207	* Lock timed out but check if this task was just
4898e640	208	* granted lock ownership - if so, pretend there
5fd691af PZ	209	* was no timeout; otherwise, cleanup lock wait.
5fd691af PZ	210	*/
4898e640 PH	211	raw_spin_lock_irq(&sem->wait_lock);
4898e640 PH	212	if (waiter.task) {
5fd691af	213	atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count);
2f588cee	214	sem->wait_readers--;
4898e640 PH	215	list_del(&waiter.list);
	216	raw_spin_unlock_irq(&sem->wait_lock);
	217	put_task_struct(waiter.task);
	218	return NULL;
	219	}
	220	raw_spin_unlock_irq(&sem->wait_lock);
	221	}
	222
	223	return sem;
	224	}
	225
	226	/*
	227	* wait for the write lock to be granted
	228	*/
	229	static struct ld_semaphore __sched *
	230	down_write_failed(struct ld_semaphore *sem, long count, long timeout)
	231	{
	232	struct ldsem_waiter waiter;
4898e640 PH	233	long adjust = -LDSEM_ACTIVE_BIAS;
	234	int locked = 0;
	235
	236	/* set up my own style of waitqueue */
	237	raw_spin_lock_irq(&sem->wait_lock);
	238
5fd691af PZ	239	/*
5fd691af PZ	240	* Try to reverse the lock attempt but if the count has changed
4898e640	241	* so that reversing fails, check if the lock is now owned,
5fd691af PZ	242	* and early-out if so.
5fd691af PZ	243	*/
4898e640	244	do {
5fd691af	245	if (atomic_long_try_cmpxchg(&sem->count, &count, count + adjust))
4898e640 PH	246	break;
	247	if ((count & LDSEM_ACTIVE_MASK) == LDSEM_ACTIVE_BIAS) {
	248	raw_spin_unlock_irq(&sem->wait_lock);
	249	return sem;
	250	}
	251	} while (1);
	252
	253	list_add_tail(&waiter.list, &sem->write_wait);
	254
5376f2e7	255	waiter.task = current;
4898e640	256
642fa448	257	set_current_state(TASK_UNINTERRUPTIBLE);
4898e640 PH	258	for (;;) {
	259	if (!timeout)
	260	break;
	261	raw_spin_unlock_irq(&sem->wait_lock);
	262	timeout = schedule_timeout(timeout);
	263	raw_spin_lock_irq(&sem->wait_lock);
642fa448	264	set_current_state(TASK_UNINTERRUPTIBLE);
f9ce5ccf GKH	265	locked = writer_trylock(sem);
f9ce5ccf GKH	266	if (locked)
4898e640 PH	267	break;
	268	}
	269
	270	if (!locked)
5fd691af	271	atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count);
4898e640	272	list_del(&waiter.list);
231f8fd0 DS	273
	274	/*
	275	* In case of timeout, wake up every reader who gave the right of way
	276	* to writer. Prevent separation readers into two groups:
	277	* one that helds semaphore and another that sleeps.
	278	* (in case of no contention with a writer)
	279	*/
	280	if (!locked && list_empty(&sem->write_wait))
	281	__ldsem_wake_readers(sem);
	282
4898e640 PH	283	raw_spin_unlock_irq(&sem->wait_lock);
4898e640 PH	284
642fa448	285	__set_current_state(TASK_RUNNING);
4898e640 PH	286
	287	/* lock wait may have timed out */
	288	if (!locked)
	289	return NULL;
	290	return sem;
	291	}
	292
	293
	294
fc0285f2	295	static int __ldsem_down_read_nested(struct ld_semaphore *sem,
4898e640 PH	296	int subclass, long timeout)
	297	{
	298	long count;
	299
c18ad0cf	300	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
4898e640	301
5fd691af	302	count = atomic_long_add_return(LDSEM_READ_BIAS, &sem->count);
4898e640	303	if (count <= 0) {
c18ad0cf	304	lock_contended(&sem->dep_map, _RET_IP_);
4898e640	305	if (!down_read_failed(sem, count, timeout)) {
c18ad0cf	306	rwsem_release(&sem->dep_map, 1, _RET_IP_);
4898e640 PH	307	return 0;
	308	}
	309	}
c18ad0cf	310	lock_acquired(&sem->dep_map, _RET_IP_);
4898e640 PH	311	return 1;
	312	}
	313
5ef6504e	314	static int __ldsem_down_write_nested(struct ld_semaphore *sem,
4898e640 PH	315	int subclass, long timeout)
	316	{
	317	long count;
	318
c18ad0cf	319	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
4898e640	320
5fd691af	321	count = atomic_long_add_return(LDSEM_WRITE_BIAS, &sem->count);
4898e640	322	if ((count & LDSEM_ACTIVE_MASK) != LDSEM_ACTIVE_BIAS) {
c18ad0cf	323	lock_contended(&sem->dep_map, _RET_IP_);
4898e640	324	if (!down_write_failed(sem, count, timeout)) {
c18ad0cf	325	rwsem_release(&sem->dep_map, 1, _RET_IP_);
4898e640 PH	326	return 0;
	327	}
	328	}
c18ad0cf	329	lock_acquired(&sem->dep_map, _RET_IP_);
4898e640 PH	330	return 1;
	331	}
	332
	333
	334	/*
	335	* lock for reading -- returns 1 if successful, 0 if timed out
	336	*/
	337	int __sched ldsem_down_read(struct ld_semaphore *sem, long timeout)
	338	{
	339	might_sleep();
	340	return __ldsem_down_read_nested(sem, 0, timeout);
	341	}
	342
	343	/*
	344	* trylock for reading -- returns 1 if successful, 0 if contention
	345	*/
	346	int ldsem_down_read_trylock(struct ld_semaphore *sem)
	347	{
5fd691af	348	long count = atomic_long_read(&sem->count);
4898e640 PH	349
4898e640 PH	350	while (count >= 0) {
5fd691af	351	if (atomic_long_try_cmpxchg(&sem->count, &count, count + LDSEM_READ_BIAS)) {
c18ad0cf PZ	352	rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
c18ad0cf PZ	353	lock_acquired(&sem->dep_map, _RET_IP_);
4898e640 PH	354	return 1;
	355	}
	356	}
	357	return 0;
	358	}
	359
	360	/*
	361	* lock for writing -- returns 1 if successful, 0 if timed out
	362	*/
	363	int __sched ldsem_down_write(struct ld_semaphore *sem, long timeout)
	364	{
	365	might_sleep();
	366	return __ldsem_down_write_nested(sem, 0, timeout);
	367	}
	368
	369	/*
	370	* trylock for writing -- returns 1 if successful, 0 if contention
	371	*/
	372	int ldsem_down_write_trylock(struct ld_semaphore *sem)
	373	{
5fd691af	374	long count = atomic_long_read(&sem->count);
4898e640 PH	375
4898e640 PH	376	while ((count & LDSEM_ACTIVE_MASK) == 0) {
5fd691af	377	if (atomic_long_try_cmpxchg(&sem->count, &count, count + LDSEM_WRITE_BIAS)) {
c18ad0cf PZ	378	rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
c18ad0cf PZ	379	lock_acquired(&sem->dep_map, _RET_IP_);
4898e640 PH	380	return 1;
	381	}
	382	}
	383	return 0;
	384	}
	385
	386	/*
	387	* release a read lock
	388	*/
	389	void ldsem_up_read(struct ld_semaphore *sem)
	390	{
	391	long count;
	392
c18ad0cf	393	rwsem_release(&sem->dep_map, 1, _RET_IP_);
4898e640	394
5fd691af	395	count = atomic_long_add_return(-LDSEM_READ_BIAS, &sem->count);
4898e640 PH	396	if (count < 0 && (count & LDSEM_ACTIVE_MASK) == 0)
	397	ldsem_wake(sem);
	398	}
	399
	400	/*
	401	* release a write lock
	402	*/
	403	void ldsem_up_write(struct ld_semaphore *sem)
	404	{
	405	long count;
	406
c18ad0cf	407	rwsem_release(&sem->dep_map, 1, _RET_IP_);
4898e640	408
5fd691af	409	count = atomic_long_add_return(-LDSEM_WRITE_BIAS, &sem->count);
4898e640 PH	410	if (count < 0)
	411	ldsem_wake(sem);
	412	}
	413
	414
	415	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	416
	417	int ldsem_down_read_nested(struct ld_semaphore *sem, int subclass, long timeout)
	418	{
	419	might_sleep();
	420	return __ldsem_down_read_nested(sem, subclass, timeout);
	421	}
	422
	423	int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
	424	long timeout)
	425	{
	426	might_sleep();
	427	return __ldsem_down_write_nested(sem, subclass, timeout);
	428	}
	429
	430	#endif