[mirror_ubuntu-bionic-kernel.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;
};

static inline long ldsem_atomic_update(long delta, struct ld_semaphore *sem)
{
	return atomic_long_add_return(delta, (atomic_long_t *)&sem->count);
}

/*
 * ldsem_cmpxchg() updates @*old with the last-known sem->count value.
 * Returns 1 if count was successfully changed; @*old will have @new value.
 * Returns 0 if count was not changed; @*old will have most recent sem->count
 */
static inline int ldsem_cmpxchg(long *old, long new, struct ld_semaphore *sem)
{
	long tmp = atomic_long_cmpxchg(&sem->count, *old, new);
	if (tmp == *old) {
		*old = new;
		return 1;
	} else {
		*old = tmp;
		return 0;
	}
}

/*
 * 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
	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 = ldsem_atomic_update(adjust, sem);
	do {
		if (count > 0)
			break;
		if (ldsem_cmpxchg(&count, count - adjust, sem))
			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 = ldsem_atomic_update(LDSEM_ACTIVE_BIAS, sem);
	do {
		if ((count & LDSEM_ACTIVE_MASK) == LDSEM_ACTIVE_BIAS)
			return 1;
		if (ldsem_cmpxchg(&count, count - LDSEM_ACTIVE_BIAS, sem))
			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 (ldsem_cmpxchg(&count, count + adjust, sem))
			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) {
			ldsem_atomic_update(-LDSEM_WAIT_BIAS, sem);
			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 (ldsem_cmpxchg(&count, count + adjust, sem))
			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)
		ldsem_atomic_update(-LDSEM_WAIT_BIAS, sem);
	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 = ldsem_atomic_update(LDSEM_READ_BIAS, sem);
	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 = ldsem_atomic_update(LDSEM_WRITE_BIAS, sem);
	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 = sem->count;

	while (count >= 0) {
		if (ldsem_cmpxchg(&count, count + LDSEM_READ_BIAS, sem)) {
			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 = sem->count;

	while ((count & LDSEM_ACTIVE_MASK) == 0) {
		if (ldsem_cmpxchg(&count, count + LDSEM_WRITE_BIAS, sem)) {
			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 = ldsem_atomic_update(-LDSEM_READ_BIAS, sem);
	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 = ldsem_atomic_update(-LDSEM_WRITE_BIAS, sem);
	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
	77	static inline long ldsem_atomic_update(long delta, struct ld_semaphore *sem)
	78	{
	79	return atomic_long_add_return(delta, (atomic_long_t *)&sem->count);
	80	}
	81
cf872776 PH	82	/*
	83	* ldsem_cmpxchg() updates @*old with the last-known sem->count value.
	84	* Returns 1 if count was successfully changed; @*old will have @new value.
	85	* Returns 0 if count was not changed; @*old will have most recent sem->count
	86	*/
4898e640 PH	87	static inline int ldsem_cmpxchg(long old, long new, struct ld_semaphore sem)
4898e640 PH	88	{
cf872776 PH	89	long tmp = atomic_long_cmpxchg(&sem->count, *old, new);
	90	if (tmp == *old) {
	91	*old = new;
	92	return 1;
	93	} else {
	94	*old = tmp;
	95	return 0;
	96	}
4898e640 PH	97	}
	98
	99	/*
	100	* Initialize an ldsem:
	101	*/
	102	void __init_ldsem(struct ld_semaphore sem, const char name,
	103	struct lock_class_key *key)
	104	{
	105	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	106	/*
	107	* Make sure we are not reinitializing a held semaphore:
	108	*/
	109	debug_check_no_locks_freed((void )sem, sizeof(sem));
	110	lockdep_init_map(&sem->dep_map, name, key, 0);
	111	#endif
	112	sem->count = LDSEM_UNLOCKED;
	113	sem->wait_readers = 0;
	114	raw_spin_lock_init(&sem->wait_lock);
	115	INIT_LIST_HEAD(&sem->read_wait);
	116	INIT_LIST_HEAD(&sem->write_wait);
	117	}
	118
	119	static void __ldsem_wake_readers(struct ld_semaphore *sem)
	120	{
	121	struct ldsem_waiter waiter, next;
	122	struct task_struct *tsk;
	123	long adjust, count;
	124
	125	/* Try to grant read locks to all readers on the read wait list.
	126	* Note the 'active part' of the count is incremented by
	127	* the number of readers before waking any processes up.
	128	*/
	129	adjust = sem->wait_readers * (LDSEM_ACTIVE_BIAS - LDSEM_WAIT_BIAS);
	130	count = ldsem_atomic_update(adjust, sem);
	131	do {
	132	if (count > 0)
	133	break;
	134	if (ldsem_cmpxchg(&count, count - adjust, sem))
	135	return;
	136	} while (1);
	137
	138	list_for_each_entry_safe(waiter, next, &sem->read_wait, list) {
	139	tsk = waiter->task;
	140	smp_mb();
	141	waiter->task = NULL;
	142	wake_up_process(tsk);
	143	put_task_struct(tsk);
	144	}
	145	INIT_LIST_HEAD(&sem->read_wait);
	146	sem->wait_readers = 0;
	147	}
	148
	149	static inline int writer_trylock(struct ld_semaphore *sem)
	150	{
	151	/* only wake this writer if the active part of the count can be
	152	* transitioned from 0 -> 1
	153	*/
	154	long count = ldsem_atomic_update(LDSEM_ACTIVE_BIAS, sem);
	155	do {
	156	if ((count & LDSEM_ACTIVE_MASK) == LDSEM_ACTIVE_BIAS)
	157	return 1;
	158	if (ldsem_cmpxchg(&count, count - LDSEM_ACTIVE_BIAS, sem))
	159	return 0;
	160	} while (1);
161	}
162
163	static void __ldsem_wake_writer(struct ld_semaphore *sem)
164	{
165	struct ldsem_waiter *waiter;
166
167	waiter = list_entry(sem->write_wait.next, struct ldsem_waiter, list);
168	wake_up_process(waiter->task);
169	}
170
171	/*
172	* handle the lock release when processes blocked on it that can now run
173	* - if we come here from up_xxxx(), then:
174	* - the 'active part' of count (&0x0000ffff) reached 0 (but may have changed)
175	* - the 'waiting part' of count (&0xffff0000) is -ve (and will still be so)
176	* - the spinlock must be held by the caller
177	* - woken process blocks are discarded from the list after having task zeroed
178	*/
179	static void __ldsem_wake(struct ld_semaphore *sem)
180	{
181	if (!list_empty(&sem->write_wait))
182	__ldsem_wake_writer(sem);
183	else if (!list_empty(&sem->read_wait))
184	__ldsem_wake_readers(sem);
185	}
186
187	static void ldsem_wake(struct ld_semaphore *sem)
188	{
189	unsigned long flags;
190
191	raw_spin_lock_irqsave(&sem->wait_lock, flags);
192	__ldsem_wake(sem);
193	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
194	}
195
196	/*
197	* wait for the read lock to be granted
198	*/
199	static struct ld_semaphore __sched *
200	down_read_failed(struct ld_semaphore *sem, long count, long timeout)
201	{
202	struct ldsem_waiter waiter;
4898e640 PH	203	long adjust = -LDSEM_ACTIVE_BIAS + LDSEM_WAIT_BIAS;
	204
	205	/* set up my own style of waitqueue */
	206	raw_spin_lock_irq(&sem->wait_lock);
	207
	208	/* Try to reverse the lock attempt but if the count has changed
	209	* so that reversing fails, check if there are are no waiters,
	210	* and early-out if not */
	211	do {
	212	if (ldsem_cmpxchg(&count, count + adjust, sem))
	213	break;
	214	if (count > 0) {
	215	raw_spin_unlock_irq(&sem->wait_lock);
	216	return sem;
	217	}
	218	} while (1);
	219
	220	list_add_tail(&waiter.list, &sem->read_wait);
	221	sem->wait_readers++;
	222
5376f2e7 DB	223	waiter.task = current;
5376f2e7 DB	224	get_task_struct(current);
4898e640 PH	225
	226	/* if there are no active locks, wake the new lock owner(s) */
	227	if ((count & LDSEM_ACTIVE_MASK) == 0)
	228	__ldsem_wake(sem);
	229
	230	raw_spin_unlock_irq(&sem->wait_lock);
	231
	232	/* wait to be given the lock */
	233	for (;;) {
642fa448	234	set_current_state(TASK_UNINTERRUPTIBLE);
4898e640 PH	235
	236	if (!waiter.task)
	237	break;
	238	if (!timeout)
	239	break;
	240	timeout = schedule_timeout(timeout);
	241	}
	242
642fa448	243	__set_current_state(TASK_RUNNING);
4898e640 PH	244
	245	if (!timeout) {
	246	/* lock timed out but check if this task was just
	247	* granted lock ownership - if so, pretend there
	248	* was no timeout; otherwise, cleanup lock wait */
	249	raw_spin_lock_irq(&sem->wait_lock);
	250	if (waiter.task) {
	251	ldsem_atomic_update(-LDSEM_WAIT_BIAS, sem);
	252	list_del(&waiter.list);
	253	raw_spin_unlock_irq(&sem->wait_lock);
	254	put_task_struct(waiter.task);
	255	return NULL;
	256	}
	257	raw_spin_unlock_irq(&sem->wait_lock);
	258	}
	259
	260	return sem;
	261	}
	262
	263	/*
	264	* wait for the write lock to be granted
	265	*/
	266	static struct ld_semaphore __sched *
	267	down_write_failed(struct ld_semaphore *sem, long count, long timeout)
	268	{
	269	struct ldsem_waiter waiter;
4898e640 PH	270	long adjust = -LDSEM_ACTIVE_BIAS;
	271	int locked = 0;
	272
	273	/* set up my own style of waitqueue */
	274	raw_spin_lock_irq(&sem->wait_lock);
	275
	276	/* Try to reverse the lock attempt but if the count has changed
	277	* so that reversing fails, check if the lock is now owned,
	278	* and early-out if so */
	279	do {
	280	if (ldsem_cmpxchg(&count, count + adjust, sem))
	281	break;
	282	if ((count & LDSEM_ACTIVE_MASK) == LDSEM_ACTIVE_BIAS) {
	283	raw_spin_unlock_irq(&sem->wait_lock);
	284	return sem;
	285	}
	286	} while (1);
	287
	288	list_add_tail(&waiter.list, &sem->write_wait);
	289
5376f2e7	290	waiter.task = current;
4898e640	291
642fa448	292	set_current_state(TASK_UNINTERRUPTIBLE);
4898e640 PH	293	for (;;) {
	294	if (!timeout)
	295	break;
	296	raw_spin_unlock_irq(&sem->wait_lock);
	297	timeout = schedule_timeout(timeout);
	298	raw_spin_lock_irq(&sem->wait_lock);
642fa448	299	set_current_state(TASK_UNINTERRUPTIBLE);
f9ce5ccf GKH	300	locked = writer_trylock(sem);
f9ce5ccf GKH	301	if (locked)
4898e640 PH	302	break;
	303	}
	304
	305	if (!locked)
	306	ldsem_atomic_update(-LDSEM_WAIT_BIAS, sem);
	307	list_del(&waiter.list);
	308	raw_spin_unlock_irq(&sem->wait_lock);
	309
642fa448	310	__set_current_state(TASK_RUNNING);
4898e640 PH	311
	312	/* lock wait may have timed out */
	313	if (!locked)
	314	return NULL;
	315	return sem;
	316	}
	317
	318
	319
fc0285f2	320	static int __ldsem_down_read_nested(struct ld_semaphore *sem,
4898e640 PH	321	int subclass, long timeout)
	322	{
	323	long count;
	324
	325	lockdep_acquire_read(sem, subclass, 0, _RET_IP_);
	326
	327	count = ldsem_atomic_update(LDSEM_READ_BIAS, sem);
	328	if (count <= 0) {
	329	lock_stat(sem, contended);
	330	if (!down_read_failed(sem, count, timeout)) {
	331	lockdep_release(sem, 1, _RET_IP_);
	332	return 0;
	333	}
	334	}
	335	lock_stat(sem, acquired);
	336	return 1;
	337	}
	338
5ef6504e	339	static int __ldsem_down_write_nested(struct ld_semaphore *sem,
4898e640 PH	340	int subclass, long timeout)
	341	{
	342	long count;
	343
	344	lockdep_acquire(sem, subclass, 0, _RET_IP_);
	345
	346	count = ldsem_atomic_update(LDSEM_WRITE_BIAS, sem);
	347	if ((count & LDSEM_ACTIVE_MASK) != LDSEM_ACTIVE_BIAS) {
	348	lock_stat(sem, contended);
	349	if (!down_write_failed(sem, count, timeout)) {
	350	lockdep_release(sem, 1, _RET_IP_);
	351	return 0;
	352	}
	353	}
	354	lock_stat(sem, acquired);
	355	return 1;
	356	}
	357
	358
	359	/*
	360	* lock for reading -- returns 1 if successful, 0 if timed out
	361	*/
	362	int __sched ldsem_down_read(struct ld_semaphore *sem, long timeout)
	363	{
	364	might_sleep();
	365	return __ldsem_down_read_nested(sem, 0, timeout);
	366	}
	367
	368	/*
	369	* trylock for reading -- returns 1 if successful, 0 if contention
	370	*/
	371	int ldsem_down_read_trylock(struct ld_semaphore *sem)
	372	{
	373	long count = sem->count;
	374
	375	while (count >= 0) {
	376	if (ldsem_cmpxchg(&count, count + LDSEM_READ_BIAS, sem)) {
	377	lockdep_acquire_read(sem, 0, 1, _RET_IP_);
	378	lock_stat(sem, acquired);
	379	return 1;
	380	}
	381	}
	382	return 0;
	383	}
	384
	385	/*
	386	* lock for writing -- returns 1 if successful, 0 if timed out
	387	*/
	388	int __sched ldsem_down_write(struct ld_semaphore *sem, long timeout)
	389	{
	390	might_sleep();
	391	return __ldsem_down_write_nested(sem, 0, timeout);
	392	}
	393
	394	/*
	395	* trylock for writing -- returns 1 if successful, 0 if contention
	396	*/
	397	int ldsem_down_write_trylock(struct ld_semaphore *sem)
	398	{
	399	long count = sem->count;
	400
	401	while ((count & LDSEM_ACTIVE_MASK) == 0) {
	402	if (ldsem_cmpxchg(&count, count + LDSEM_WRITE_BIAS, sem)) {
	403	lockdep_acquire(sem, 0, 1, _RET_IP_);
404	lock_stat(sem, acquired);
405	return 1;
406	}
407	}
408	return 0;
409	}
410
411	/*
412	* release a read lock
413	*/
414	void ldsem_up_read(struct ld_semaphore *sem)
415	{
416	long count;
417
418	lockdep_release(sem, 1, _RET_IP_);
419
420	count = ldsem_atomic_update(-LDSEM_READ_BIAS, sem);
421	if (count < 0 && (count & LDSEM_ACTIVE_MASK) == 0)
422	ldsem_wake(sem);
423	}
424
425	/*
426	* release a write lock
427	*/
428	void ldsem_up_write(struct ld_semaphore *sem)
429	{
430	long count;
431
432	lockdep_release(sem, 1, _RET_IP_);
433
434	count = ldsem_atomic_update(-LDSEM_WRITE_BIAS, sem);
435	if (count < 0)
436	ldsem_wake(sem);
437	}
438
439
440	#ifdef CONFIG_DEBUG_LOCK_ALLOC
441
442	int ldsem_down_read_nested(struct ld_semaphore *sem, int subclass, long timeout)
443	{
444	might_sleep();
445	return __ldsem_down_read_nested(sem, subclass, timeout);
446	}
447
448	int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
449	long timeout)
450	{
451	might_sleep();
452	return __ldsem_down_write_nested(sem, subclass, timeout);
453	}
454
455	#endif