[mirror_ubuntu-zesty-kernel.git] / include / asm-x86_64 / rwsem.h

/* rwsem.h: R/W semaphores implemented using XADD/CMPXCHG for x86_64+
 *
 * Written by David Howells (dhowells@redhat.com).
 * Ported by Andi Kleen <ak@suse.de> to x86-64.
 *
 * Derived from asm-i386/semaphore.h and asm-i386/rwsem.h
 *
 *
 * The MSW of the count is the negated number of active writers and waiting
 * lockers, and the LSW is the total number of active locks
 *
 * The lock count is initialized to 0 (no active and no waiting lockers).
 *
 * When a writer subtracts WRITE_BIAS, it'll get 0xffff0001 for the case of an
 * uncontended lock. This can be determined because XADD returns the old value.
 * Readers increment by 1 and see a positive value when uncontended, negative
 * if there are writers (and maybe) readers waiting (in which case it goes to
 * sleep).
 *
 * The value of WAITING_BIAS supports up to 32766 waiting processes. This can
 * be extended to 65534 by manually checking the whole MSW rather than relying
 * on the S flag.
 *
 * The value of ACTIVE_BIAS supports up to 65535 active processes.
 *
 * This should be totally fair - if anything is waiting, a process that wants a
 * lock will go to the back of the queue. When the currently active lock is
 * released, if there's a writer at the front of the queue, then that and only
 * that will be woken up; if there's a bunch of consecutive readers at the
 * front, then they'll all be woken up, but no other readers will be.
 */

#ifndef _X8664_RWSEM_H
#define _X8664_RWSEM_H

#ifndef _LINUX_RWSEM_H
#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
#endif

#ifdef __KERNEL__

#include <linux/list.h>
#include <linux/spinlock.h>

struct rwsem_waiter;

extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);

/*
 * the semaphore definition
 */
struct rw_semaphore {
	signed int		count;
#define RWSEM_UNLOCKED_VALUE		0x00000000
#define RWSEM_ACTIVE_BIAS		0x00000001
#define RWSEM_ACTIVE_MASK		0x0000ffff
#define RWSEM_WAITING_BIAS		(-0x00010000)
#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
	spinlock_t		wait_lock;
	struct list_head	wait_list;
#if RWSEM_DEBUG
	int			debug;
#endif
};

/*
 * initialisation
 */
#if RWSEM_DEBUG
#define __RWSEM_DEBUG_INIT      , 0
#else
#define __RWSEM_DEBUG_INIT	/* */
#endif

#define __RWSEM_INITIALIZER(name) \
{ RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, LIST_HEAD_INIT((name).wait_list) \
	__RWSEM_DEBUG_INIT }

#define DECLARE_RWSEM(name) \
	struct rw_semaphore name = __RWSEM_INITIALIZER(name)

static inline void init_rwsem(struct rw_semaphore *sem)
{
	sem->count = RWSEM_UNLOCKED_VALUE;
	spin_lock_init(&sem->wait_lock);
	INIT_LIST_HEAD(&sem->wait_list);
#if RWSEM_DEBUG
	sem->debug = 0;
#endif
}

/*
 * lock for reading
 */
static inline void __down_read(struct rw_semaphore *sem)
{
	__asm__ __volatile__(
		"# beginning down_read\n\t"
LOCK_PREFIX	"  incl      (%%rdi)\n\t" /* adds 0x00000001, returns the old value */
		"  js        2f\n\t" /* jump if we weren't granted the lock */
		"1:\n\t"
		LOCK_SECTION_START("") \
		"2:\n\t"
		"  call      rwsem_down_read_failed_thunk\n\t"
		"  jmp       1b\n"
		LOCK_SECTION_END \
		"# ending down_read\n\t"
		: "+m"(sem->count)
		: "D"(sem)
		: "memory", "cc");
}


/*
 * trylock for reading -- returns 1 if successful, 0 if contention
 */
static inline int __down_read_trylock(struct rw_semaphore *sem)
{
	__s32 result, tmp;
	__asm__ __volatile__(
		"# beginning __down_read_trylock\n\t"
		"  movl      %0,%1\n\t"
		"1:\n\t"
		"  movl	     %1,%2\n\t"
		"  addl      %3,%2\n\t"
		"  jle	     2f\n\t"
LOCK_PREFIX	"  cmpxchgl  %2,%0\n\t"
		"  jnz	     1b\n\t"
		"2:\n\t"
		"# ending __down_read_trylock\n\t"
		: "+m"(sem->count), "=&a"(result), "=&r"(tmp)
		: "i"(RWSEM_ACTIVE_READ_BIAS)
		: "memory", "cc");
	return result>=0 ? 1 : 0;
}


/*
 * lock for writing
 */
static inline void __down_write(struct rw_semaphore *sem)
{
	int tmp;

	tmp = RWSEM_ACTIVE_WRITE_BIAS;
	__asm__ __volatile__(
		"# beginning down_write\n\t"
LOCK_PREFIX	"  xaddl      %0,(%%rdi)\n\t" /* subtract 0x0000ffff, returns the old value */
		"  testl     %0,%0\n\t" /* was the count 0 before? */
		"  jnz       2f\n\t" /* jump if we weren't granted the lock */
		"1:\n\t"
		LOCK_SECTION_START("")
		"2:\n\t"
		"  call      rwsem_down_write_failed_thunk\n\t"
		"  jmp       1b\n"
		LOCK_SECTION_END
		"# ending down_write"
		: "=&r" (tmp) 
		: "0"(tmp), "D"(sem)
		: "memory", "cc");
}

/*
 * trylock for writing -- returns 1 if successful, 0 if contention
 */
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
	signed long ret = cmpxchg(&sem->count,
				  RWSEM_UNLOCKED_VALUE, 
				  RWSEM_ACTIVE_WRITE_BIAS);
	if (ret == RWSEM_UNLOCKED_VALUE)
		return 1;
	return 0;
}

/*
 * unlock after reading
 */
static inline void __up_read(struct rw_semaphore *sem)
{
	__s32 tmp = -RWSEM_ACTIVE_READ_BIAS;
	__asm__ __volatile__(
		"# beginning __up_read\n\t"
LOCK_PREFIX	"  xaddl      %[tmp],(%%rdi)\n\t" /* subtracts 1, returns the old value */
		"  js        2f\n\t" /* jump if the lock is being waited upon */
		"1:\n\t"
		LOCK_SECTION_START("")
		"2:\n\t"
		"  decw      %w[tmp]\n\t" /* do nothing if still outstanding active readers */
		"  jnz       1b\n\t"
		"  call      rwsem_wake_thunk\n\t"
		"  jmp       1b\n"
		LOCK_SECTION_END
		"# ending __up_read\n"
		: "+m"(sem->count), [tmp] "+r" (tmp)
		: "D"(sem)
		: "memory", "cc");
}

/*
 * unlock after writing
 */
static inline void __up_write(struct rw_semaphore *sem)
{
	unsigned tmp; 
	__asm__ __volatile__(
		"# beginning __up_write\n\t"
		"  movl     %[bias],%[tmp]\n\t"
LOCK_PREFIX	"  xaddl     %[tmp],(%%rdi)\n\t" /* tries to transition 0xffff0001 -> 0x00000000 */
		"  jnz       2f\n\t" /* jump if the lock is being waited upon */
		"1:\n\t"
		LOCK_SECTION_START("")
		"2:\n\t"
		"  decw      %w[tmp]\n\t" /* did the active count reduce to 0? */
		"  jnz       1b\n\t" /* jump back if not */
		"  call      rwsem_wake_thunk\n\t"
		"  jmp       1b\n"
		LOCK_SECTION_END
		"# ending __up_write\n"
		: "+m"(sem->count), [tmp] "=r" (tmp)
		: "D"(sem), [bias] "i"(-RWSEM_ACTIVE_WRITE_BIAS)
		: "memory", "cc");
}

/*
 * downgrade write lock to read lock
 */
static inline void __downgrade_write(struct rw_semaphore *sem)
{
	__asm__ __volatile__(
		"# beginning __downgrade_write\n\t"
LOCK_PREFIX	"  addl      %[bias],(%%rdi)\n\t" /* transitions 0xZZZZ0001 -> 0xYYYY0001 */
		"  js        2f\n\t" /* jump if the lock is being waited upon */
		"1:\n\t"
		LOCK_SECTION_START("")
		"2:\n\t"
		"  call	     rwsem_downgrade_thunk\n"
		"  jmp       1b\n"
		LOCK_SECTION_END
		"# ending __downgrade_write\n"
		: "=m"(sem->count)
		: "D"(sem), [bias] "i"(-RWSEM_WAITING_BIAS), "m"(sem->count)
		: "memory", "cc");
}

/*
 * implement atomic add functionality
 */
static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
{
	__asm__ __volatile__(
LOCK_PREFIX	"addl %1,%0"
		:"=m"(sem->count)
		:"ir"(delta), "m"(sem->count));
}

/*
 * implement exchange and add functionality
 */
static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
{
	int tmp = delta;

	__asm__ __volatile__(
LOCK_PREFIX	"xaddl %0,(%2)"
		: "=r"(tmp), "=m"(sem->count)
		: "r"(sem), "m"(sem->count), "0" (tmp)
		: "memory");

	return tmp+delta;
}

#endif /* __KERNEL__ */
#endif /* _X8664_RWSEM_H */
Commit	Line	Data
1da177e4 LT	1	/* rwsem.h: R/W semaphores implemented using XADD/CMPXCHG for x86_64+
	2	*
	3	* Written by David Howells (dhowells@redhat.com).
	4	* Ported by Andi Kleen <ak@suse.de> to x86-64.
	5	*
	6	* Derived from asm-i386/semaphore.h and asm-i386/rwsem.h
	7	*
	8	*
	9	* The MSW of the count is the negated number of active writers and waiting
	10	* lockers, and the LSW is the total number of active locks
	11	*
	12	* The lock count is initialized to 0 (no active and no waiting lockers).
	13	*
	14	* When a writer subtracts WRITE_BIAS, it'll get 0xffff0001 for the case of an
	15	* uncontended lock. This can be determined because XADD returns the old value.
	16	* Readers increment by 1 and see a positive value when uncontended, negative
	17	* if there are writers (and maybe) readers waiting (in which case it goes to
	18	* sleep).
	19	*
	20	* The value of WAITING_BIAS supports up to 32766 waiting processes. This can
	21	* be extended to 65534 by manually checking the whole MSW rather than relying
	22	* on the S flag.
	23	*
	24	* The value of ACTIVE_BIAS supports up to 65535 active processes.
	25	*
	26	* This should be totally fair - if anything is waiting, a process that wants a
	27	* lock will go to the back of the queue. When the currently active lock is
	28	* released, if there's a writer at the front of the queue, then that and only
	29	* that will be woken up; if there's a bunch of consecutive readers at the
	30	* front, then they'll all be woken up, but no other readers will be.
	31	*/
	32
	33	#ifndef _X8664_RWSEM_H
	34	#define _X8664_RWSEM_H
	35
	36	#ifndef _LINUX_RWSEM_H
	37	#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
	38	#endif
	39
	40	#ifdef __KERNEL__
	41
	42	#include <linux/list.h>
	43	#include <linux/spinlock.h>
	44
	45	struct rwsem_waiter;
	46
	47	extern struct rw_semaphore rwsem_down_read_failed(struct rw_semaphore sem);
	48	extern struct rw_semaphore rwsem_down_write_failed(struct rw_semaphore sem);
	49	extern struct rw_semaphore rwsem_wake(struct rw_semaphore );
	50	extern struct rw_semaphore rwsem_downgrade_wake(struct rw_semaphore sem);
	51
	52	/*
	53	* the semaphore definition
	54	*/
	55	struct rw_semaphore {
	56	signed int count;
	57	#define RWSEM_UNLOCKED_VALUE 0x00000000
	58	#define RWSEM_ACTIVE_BIAS 0x00000001
	59	#define RWSEM_ACTIVE_MASK 0x0000ffff
	60	#define RWSEM_WAITING_BIAS (-0x00010000)
	61	#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
	62	#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
	63	spinlock_t wait_lock;
	64	struct list_head wait_list;
65	#if RWSEM_DEBUG
66	int debug;
67	#endif
68	};
69
70	/*
71	* initialisation
72	*/
73	#if RWSEM_DEBUG
74	#define __RWSEM_DEBUG_INIT , 0
75	#else
76	#define __RWSEM_DEBUG_INIT /* */
77	#endif
78
79	#define __RWSEM_INITIALIZER(name) \
80	{ RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, LIST_HEAD_INIT((name).wait_list) \
81	__RWSEM_DEBUG_INIT }
82
83	#define DECLARE_RWSEM(name) \
84	struct rw_semaphore name = __RWSEM_INITIALIZER(name)
85
86	static inline void init_rwsem(struct rw_semaphore *sem)
87	{
88	sem->count = RWSEM_UNLOCKED_VALUE;
89	spin_lock_init(&sem->wait_lock);
90	INIT_LIST_HEAD(&sem->wait_list);
91	#if RWSEM_DEBUG
92	sem->debug = 0;
93	#endif
94	}
95
96	/*
97	* lock for reading
98	*/
99	static inline void __down_read(struct rw_semaphore *sem)
100	{
101	__asm__ __volatile__(
102	"# beginning down_read\n\t"
103	LOCK_PREFIX " incl (%%rdi)\n\t" /* adds 0x00000001, returns the old value */
104	" js 2f\n\t" /* jump if we weren't granted the lock */
105	"1:\n\t"
106	LOCK_SECTION_START("") \
107	"2:\n\t"
108	" call rwsem_down_read_failed_thunk\n\t"
109	" jmp 1b\n"
110	LOCK_SECTION_END \
111	"# ending down_read\n\t"
112	: "+m"(sem->count)
113	: "D"(sem)
114	: "memory", "cc");
115	}
116
117
118	/*
119	* trylock for reading -- returns 1 if successful, 0 if contention
120	*/
121	static inline int __down_read_trylock(struct rw_semaphore *sem)
122	{
123	__s32 result, tmp;
124	__asm__ __volatile__(
125	"# beginning __down_read_trylock\n\t"
126	" movl %0,%1\n\t"
127	"1:\n\t"
128	" movl %1,%2\n\t"
129	" addl %3,%2\n\t"
130	" jle 2f\n\t"
131	LOCK_PREFIX " cmpxchgl %2,%0\n\t"
132	" jnz 1b\n\t"
133	"2:\n\t"
134	"# ending __down_read_trylock\n\t"
135	: "+m"(sem->count), "=&a"(result), "=&r"(tmp)
136	: "i"(RWSEM_ACTIVE_READ_BIAS)
137	: "memory", "cc");
138	return result>=0 ? 1 : 0;
139	}
140
141
142	/*
143	* lock for writing
144	*/
145	static inline void __down_write(struct rw_semaphore *sem)
146	{
147	int tmp;
148
149	tmp = RWSEM_ACTIVE_WRITE_BIAS;
150	__asm__ __volatile__(
151	"# beginning down_write\n\t"
152	LOCK_PREFIX " xaddl %0,(%%rdi)\n\t" /* subtract 0x0000ffff, returns the old value */
153	" testl %0,%0\n\t" /* was the count 0 before? */
154	" jnz 2f\n\t" /* jump if we weren't granted the lock */
155	"1:\n\t"
156	LOCK_SECTION_START("")
157	"2:\n\t"
158	" call rwsem_down_write_failed_thunk\n\t"
159	" jmp 1b\n"
160	LOCK_SECTION_END
161	"# ending down_write"
162	: "=&r" (tmp)
163	: "0"(tmp), "D"(sem)
164	: "memory", "cc");
165	}
166
167	/*
168	* trylock for writing -- returns 1 if successful, 0 if contention
169	*/
170	static inline int __down_write_trylock(struct rw_semaphore *sem)
171	{
172	signed long ret = cmpxchg(&sem->count,
173	RWSEM_UNLOCKED_VALUE,
174	RWSEM_ACTIVE_WRITE_BIAS);
175	if (ret == RWSEM_UNLOCKED_VALUE)
176	return 1;
177	return 0;
178	}
179
180	/*
181	* unlock after reading
182	*/
183	static inline void __up_read(struct rw_semaphore *sem)
184	{
185	__s32 tmp = -RWSEM_ACTIVE_READ_BIAS;
186	__asm__ __volatile__(
187	"# beginning __up_read\n\t"
188	LOCK_PREFIX " xaddl %[tmp],(%%rdi)\n\t" /* subtracts 1, returns the old value */
189	" js 2f\n\t" /* jump if the lock is being waited upon */
190	"1:\n\t"
191	LOCK_SECTION_START("")
192	"2:\n\t"
193	" decw %w[tmp]\n\t" /* do nothing if still outstanding active readers */
194	" jnz 1b\n\t"
195	" call rwsem_wake_thunk\n\t"
196	" jmp 1b\n"
197	LOCK_SECTION_END
198	"# ending __up_read\n"
199	: "+m"(sem->count), [tmp] "+r" (tmp)
200	: "D"(sem)
201	: "memory", "cc");
202	}
203
204	/*
205	* unlock after writing
206	*/
207	static inline void __up_write(struct rw_semaphore *sem)
208	{
209	unsigned tmp;
210	__asm__ __volatile__(
211	"# beginning __up_write\n\t"
212	" movl %[bias],%[tmp]\n\t"
213	LOCK_PREFIX " xaddl %[tmp],(%%rdi)\n\t" /* tries to transition 0xffff0001 -> 0x00000000 */
214	" jnz 2f\n\t" /* jump if the lock is being waited upon */
215	"1:\n\t"
216	LOCK_SECTION_START("")
217	"2:\n\t"
218	" decw %w[tmp]\n\t" /* did the active count reduce to 0? */
219	" jnz 1b\n\t" /* jump back if not */
220	" call rwsem_wake_thunk\n\t"
221	" jmp 1b\n"
222	LOCK_SECTION_END
223	"# ending __up_write\n"
224	: "+m"(sem->count), [tmp] "=r" (tmp)
225	: "D"(sem), [bias] "i"(-RWSEM_ACTIVE_WRITE_BIAS)
226	: "memory", "cc");
227	}
228
229	/*
230	* downgrade write lock to read lock
231	*/
232	static inline void __downgrade_write(struct rw_semaphore *sem)
233	{
234	__asm__ __volatile__(
235	"# beginning __downgrade_write\n\t"
236	LOCK_PREFIX " addl %[bias],(%%rdi)\n\t" /* transitions 0xZZZZ0001 -> 0xYYYY0001 */
237	" js 2f\n\t" /* jump if the lock is being waited upon */
238	"1:\n\t"
239	LOCK_SECTION_START("")
240	"2:\n\t"
241	" call rwsem_downgrade_thunk\n"
242	" jmp 1b\n"
243	LOCK_SECTION_END
244	"# ending __downgrade_write\n"
245	: "=m"(sem->count)
246	: "D"(sem), [bias] "i"(-RWSEM_WAITING_BIAS), "m"(sem->count)
247	: "memory", "cc");
248	}
249
250	/*
251	* implement atomic add functionality
252	*/
253	static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
254	{
255	__asm__ __volatile__(
256	LOCK_PREFIX "addl %1,%0"
257	:"=m"(sem->count)
258	:"ir"(delta), "m"(sem->count));
259	}
260
261	/*
262	* implement exchange and add functionality
263	*/
264	static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
265	{
266	int tmp = delta;
267
268	__asm__ __volatile__(
269	LOCK_PREFIX "xaddl %0,(%2)"
270	: "=r"(tmp), "=m"(sem->count)
271	: "r"(sem), "m"(sem->count), "0" (tmp)
272	: "memory");
273
274	return tmp+delta;
275	}
276
277	#endif /* __KERNEL__ */
278	#endif /* _X8664_RWSEM_H */