[mirror_ubuntu-bionic-kernel.git] / arch / x86 / include / asm / rwsem.h

/* rwsem.h: R/W semaphores implemented using XADD/CMPXCHG for i486+
 *
 * Written by David Howells (dhowells@redhat.com).
 *
 * Derived from asm-x86/semaphore.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 consequtive readers at the
 * front, then they'll all be woken up, but no other readers will be.
 */

#ifndef _ASM_X86_RWSEM_H
#define _ASM_X86_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>
#include <linux/lockdep.h>
#include <asm/asm.h>

struct rwsem_waiter;

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

/*
 * the semaphore definition
 *
 * The bias values and the counter type limits the number of
 * potential readers/writers to 32767 for 32 bits and 2147483647
 * for 64 bits.
 */

#ifdef CONFIG_X86_64
# define RWSEM_ACTIVE_MASK		0xffffffffL
#else
# define RWSEM_ACTIVE_MASK		0x0000ffffL
#endif

#define RWSEM_UNLOCKED_VALUE		0x00000000L
#define RWSEM_ACTIVE_BIAS		0x00000001L
#define RWSEM_WAITING_BIAS		(-RWSEM_ACTIVE_MASK-1)
#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)

typedef signed long rwsem_count_t;

struct rw_semaphore {
	rwsem_count_t		count;
	spinlock_t		wait_lock;
	struct list_head	wait_list;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
	struct lockdep_map dep_map;
#endif
};

#ifdef CONFIG_DEBUG_LOCK_ALLOC
# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
#else
# define __RWSEM_DEP_MAP_INIT(lockname)
#endif


#define __RWSEM_INITIALIZER(name)				\
{								\
	RWSEM_UNLOCKED_VALUE, __SPIN_LOCK_UNLOCKED((name).wait_lock), \
	LIST_HEAD_INIT((name).wait_list) __RWSEM_DEP_MAP_INIT(name) \
}

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

extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
			 struct lock_class_key *key);

#define init_rwsem(sem)						\
do {								\
	static struct lock_class_key __key;			\
								\
	__init_rwsem((sem), #sem, &__key);			\
} while (0)

/*
 * lock for reading
 */
static inline void __down_read(struct rw_semaphore *sem)
{
	asm volatile("# beginning down_read\n\t"
		     LOCK_PREFIX _ASM_INC "(%1)\n\t"
		     /* adds 0x00000001, returns the old value */
		     "  jns        1f\n"
		     "  call call_rwsem_down_read_failed\n"
		     "1:\n\t"
		     "# ending down_read\n\t"
		     : "+m" (sem->count)
		     : "a" (sem)
		     : "memory", "cc");
}

/*
 * trylock for reading -- returns 1 if successful, 0 if contention
 */
static inline int __down_read_trylock(struct rw_semaphore *sem)
{
	rwsem_count_t result, tmp;
	asm volatile("# beginning __down_read_trylock\n\t"
		     "  mov          %0,%1\n\t"
		     "1:\n\t"
		     "  mov          %1,%2\n\t"
		     "  add          %3,%2\n\t"
		     "  jle	     2f\n\t"
		     LOCK_PREFIX "  cmpxchg  %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_nested(struct rw_semaphore *sem, int subclass)
{
	rwsem_count_t tmp;

	tmp = RWSEM_ACTIVE_WRITE_BIAS;
	asm volatile("# beginning down_write\n\t"
		     LOCK_PREFIX "  xadd      %1,(%2)\n\t"
		     /* subtract 0x0000ffff, returns the old value */
		     "  test      %1,%1\n\t"
		     /* was the count 0 before? */
		     "  jz        1f\n"
		     "  call call_rwsem_down_write_failed\n"
		     "1:\n"
		     "# ending down_write"
		     : "+m" (sem->count), "=d" (tmp)
		     : "a" (sem), "1" (tmp)
		     : "memory", "cc");
}

static inline void __down_write(struct rw_semaphore *sem)
{
	__down_write_nested(sem, 0);
}

/*
 * trylock for writing -- returns 1 if successful, 0 if contention
 */
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
	rwsem_count_t 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)
{
	rwsem_count_t tmp = -RWSEM_ACTIVE_READ_BIAS;
	asm volatile("# beginning __up_read\n\t"
		     LOCK_PREFIX "  xadd      %1,(%2)\n\t"
		     /* subtracts 1, returns the old value */
		     "  jns        1f\n\t"
		     "  call call_rwsem_wake\n"
		     "1:\n"
		     "# ending __up_read\n"
		     : "+m" (sem->count), "=d" (tmp)
		     : "a" (sem), "1" (tmp)
		     : "memory", "cc");
}

/*
 * unlock after writing
 */
static inline void __up_write(struct rw_semaphore *sem)
{
	rwsem_count_t tmp;
	asm volatile("# beginning __up_write\n\t"
		     LOCK_PREFIX "  xadd      %1,(%2)\n\t"
		     /* tries to transition
			0xffff0001 -> 0x00000000 */
		     "  jz       1f\n"
		     "  call call_rwsem_wake\n"
		     "1:\n\t"
		     "# ending __up_write\n"
		     : "+m" (sem->count), "=d" (tmp)
		     : "a" (sem), "1" (-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 _ASM_ADD "%2,(%1)\n\t"
		     /*
		      * transitions 0xZZZZ0001 -> 0xYYYY0001 (i386)
		      *     0xZZZZZZZZ00000001 -> 0xYYYYYYYY00000001 (x86_64)
		      */
		     "  jns       1f\n\t"
		     "  call call_rwsem_downgrade_wake\n"
		     "1:\n\t"
		     "# ending __downgrade_write\n"
		     : "+m" (sem->count)
		     : "a" (sem), "er" (-RWSEM_WAITING_BIAS)
		     : "memory", "cc");
}

/*
 * implement atomic add functionality
 */
static inline void rwsem_atomic_add(rwsem_count_t delta,
				    struct rw_semaphore *sem)
{
	asm volatile(LOCK_PREFIX _ASM_ADD "%1,%0"
		     : "+m" (sem->count)
		     : "er" (delta));
}

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

	asm volatile(LOCK_PREFIX "xadd %0,%1"
		     : "+r" (tmp), "+m" (sem->count)
		     : : "memory");

	return tmp + delta;
}

static inline int rwsem_is_locked(struct rw_semaphore *sem)
{
	return (sem->count != 0);
}

#endif /* __KERNEL__ */
#endif /* _ASM_X86_RWSEM_H */
Commit	Line	Data
1da177e4 LT	1	/* rwsem.h: R/W semaphores implemented using XADD/CMPXCHG for i486+
	2	*
	3	* Written by David Howells (dhowells@redhat.com).
	4	*
99122a3f	5	* Derived from asm-x86/semaphore.h
1da177e4 LT	6	*
	7	*
	8	* The MSW of the count is the negated number of active writers and waiting
	9	* lockers, and the LSW is the total number of active locks
	10	*
	11	* The lock count is initialized to 0 (no active and no waiting lockers).
	12	*
	13	* When a writer subtracts WRITE_BIAS, it'll get 0xffff0001 for the case of an
	14	* uncontended lock. This can be determined because XADD returns the old value.
	15	* Readers increment by 1 and see a positive value when uncontended, negative
	16	* if there are writers (and maybe) readers waiting (in which case it goes to
	17	* sleep).
	18	*
	19	* The value of WAITING_BIAS supports up to 32766 waiting processes. This can
	20	* be extended to 65534 by manually checking the whole MSW rather than relying
	21	* on the S flag.
	22	*
	23	* The value of ACTIVE_BIAS supports up to 65535 active processes.
	24	*
	25	* This should be totally fair - if anything is waiting, a process that wants a
	26	* lock will go to the back of the queue. When the currently active lock is
	27	* released, if there's a writer at the front of the queue, then that and only
	28	* that will be woken up; if there's a bunch of consequtive readers at the
	29	* front, then they'll all be woken up, but no other readers will be.
	30	*/
	31
1965aae3 PA	32	#ifndef _ASM_X86_RWSEM_H
1965aae3 PA	33	#define _ASM_X86_RWSEM_H
1da177e4 LT	34
	35	#ifndef _LINUX_RWSEM_H
	36	#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
	37	#endif
	38
	39	#ifdef __KERNEL__
	40
	41	#include <linux/list.h>
	42	#include <linux/spinlock.h>
4ea2176d	43	#include <linux/lockdep.h>
1838ef1d	44	#include <asm/asm.h>
1da177e4 LT	45
	46	struct rwsem_waiter;
	47
d50efc6c IM	48	extern asmregparm struct rw_semaphore *
	49	rwsem_down_read_failed(struct rw_semaphore *sem);
	50	extern asmregparm struct rw_semaphore *
	51	rwsem_down_write_failed(struct rw_semaphore *sem);
	52	extern asmregparm struct rw_semaphore *
	53	rwsem_wake(struct rw_semaphore *);
	54	extern asmregparm struct rw_semaphore *
	55	rwsem_downgrade_wake(struct rw_semaphore *sem);
1da177e4 LT	56
	57	/*
	58	* the semaphore definition
5d0b7235	59	*
1838ef1d PA	60	* The bias values and the counter type limits the number of
	61	* potential readers/writers to 32767 for 32 bits and 2147483647
	62	* for 64 bits.
1da177e4	63	*/
6e5609a9	64
1838ef1d PA	65	#ifdef CONFIG_X86_64
	66	# define RWSEM_ACTIVE_MASK 0xffffffffL
	67	#else
	68	# define RWSEM_ACTIVE_MASK 0x0000ffffL
	69	#endif
	70
	71	#define RWSEM_UNLOCKED_VALUE 0x00000000L
	72	#define RWSEM_ACTIVE_BIAS 0x00000001L
	73	#define RWSEM_WAITING_BIAS (-RWSEM_ACTIVE_MASK-1)
1da177e4 LT	74	#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
1da177e4 LT	75	#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
6e5609a9	76
1838ef1d	77	typedef signed long rwsem_count_t;
5d0b7235	78
6e5609a9	79	struct rw_semaphore {
5d0b7235	80	rwsem_count_t count;
1da177e4 LT	81	spinlock_t wait_lock;
1da177e4 LT	82	struct list_head wait_list;
4ea2176d IM	83	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	84	struct lockdep_map dep_map;
	85	#endif
1da177e4 LT	86	};
1da177e4 LT	87
4ea2176d IM	88	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	89	# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
	90	#else
	91	# define __RWSEM_DEP_MAP_INIT(lockname)
	92	#endif
	93
	94
6e5609a9 JP	95	#define __RWSEM_INITIALIZER(name) \
	96	{ \
	97	RWSEM_UNLOCKED_VALUE, __SPIN_LOCK_UNLOCKED((name).wait_lock), \
	98	LIST_HEAD_INIT((name).wait_list) __RWSEM_DEP_MAP_INIT(name) \
	99	}
1da177e4	100
6e5609a9	101	#define DECLARE_RWSEM(name) \
1da177e4 LT	102	struct rw_semaphore name = __RWSEM_INITIALIZER(name)
1da177e4 LT	103
4ea2176d IM	104	extern void __init_rwsem(struct rw_semaphore sem, const char name,
	105	struct lock_class_key *key);
	106
	107	#define init_rwsem(sem) \
	108	do { \
	109	static struct lock_class_key __key; \
	110	\
	111	__init_rwsem((sem), #sem, &__key); \
	112	} while (0)
1da177e4 LT	113
	114	/*
	115	* lock for reading
	116	*/
	117	static inline void __down_read(struct rw_semaphore *sem)
	118	{
6e5609a9	119	asm volatile("# beginning down_read\n\t"
1838ef1d	120	LOCK_PREFIX _ASM_INC "(%1)\n\t"
6e5609a9 JP	121	/* adds 0x00000001, returns the old value */
	122	" jns 1f\n"
	123	" call call_rwsem_down_read_failed\n"
	124	"1:\n\t"
	125	"# ending down_read\n\t"
	126	: "+m" (sem->count)
	127	: "a" (sem)
	128	: "memory", "cc");
1da177e4 LT	129	}
	130
	131	/*
	132	* trylock for reading -- returns 1 if successful, 0 if contention
	133	*/
	134	static inline int __down_read_trylock(struct rw_semaphore *sem)
	135	{
5d0b7235	136	rwsem_count_t result, tmp;
6e5609a9	137	asm volatile("# beginning __down_read_trylock\n\t"
59c33fa7	138	" mov %0,%1\n\t"
6e5609a9	139	"1:\n\t"
59c33fa7 LT	140	" mov %1,%2\n\t"
59c33fa7 LT	141	" add %3,%2\n\t"
6e5609a9	142	" jle 2f\n\t"
59c33fa7	143	LOCK_PREFIX " cmpxchg %2,%0\n\t"
6e5609a9 JP	144	" jnz 1b\n\t"
	145	"2:\n\t"
	146	"# ending __down_read_trylock\n\t"
	147	: "+m" (sem->count), "=&a" (result), "=&r" (tmp)
	148	: "i" (RWSEM_ACTIVE_READ_BIAS)
	149	: "memory", "cc");
	150	return result >= 0 ? 1 : 0;
1da177e4 LT	151	}
	152
	153	/*
	154	* lock for writing
	155	*/
4ea2176d	156	static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
1da177e4	157	{
5d0b7235	158	rwsem_count_t tmp;
1da177e4 LT	159
1da177e4 LT	160	tmp = RWSEM_ACTIVE_WRITE_BIAS;
6e5609a9	161	asm volatile("# beginning down_write\n\t"
59c33fa7	162	LOCK_PREFIX " xadd %1,(%2)\n\t"
6e5609a9	163	/* subtract 0x0000ffff, returns the old value */
59c33fa7	164	" test %1,%1\n\t"
6e5609a9 JP	165	/* was the count 0 before? */
	166	" jz 1f\n"
	167	" call call_rwsem_down_write_failed\n"
	168	"1:\n"
	169	"# ending down_write"
	170	: "+m" (sem->count), "=d" (tmp)
	171	: "a" (sem), "1" (tmp)
	172	: "memory", "cc");
1da177e4 LT	173	}
1da177e4 LT	174
4ea2176d IM	175	static inline void __down_write(struct rw_semaphore *sem)
	176	{
	177	__down_write_nested(sem, 0);
	178	}
	179
1da177e4 LT	180	/*
	181	* trylock for writing -- returns 1 if successful, 0 if contention
	182	*/
	183	static inline int __down_write_trylock(struct rw_semaphore *sem)
	184	{
5d0b7235 LT	185	rwsem_count_t ret = cmpxchg(&sem->count,
	186	RWSEM_UNLOCKED_VALUE,
	187	RWSEM_ACTIVE_WRITE_BIAS);
1da177e4 LT	188	if (ret == RWSEM_UNLOCKED_VALUE)
	189	return 1;
	190	return 0;
	191	}
	192
	193	/*
	194	* unlock after reading
	195	*/
	196	static inline void __up_read(struct rw_semaphore *sem)
	197	{
5d0b7235	198	rwsem_count_t tmp = -RWSEM_ACTIVE_READ_BIAS;
6e5609a9	199	asm volatile("# beginning __up_read\n\t"
59c33fa7	200	LOCK_PREFIX " xadd %1,(%2)\n\t"
6e5609a9 JP	201	/* subtracts 1, returns the old value */
	202	" jns 1f\n\t"
	203	" call call_rwsem_wake\n"
	204	"1:\n"
	205	"# ending __up_read\n"
	206	: "+m" (sem->count), "=d" (tmp)
	207	: "a" (sem), "1" (tmp)
	208	: "memory", "cc");
1da177e4 LT	209	}
	210
	211	/*
	212	* unlock after writing
	213	*/
	214	static inline void __up_write(struct rw_semaphore *sem)
	215	{
5d0b7235	216	rwsem_count_t tmp;
6e5609a9	217	asm volatile("# beginning __up_write\n\t"
59c33fa7	218	LOCK_PREFIX " xadd %1,(%2)\n\t"
6e5609a9 JP	219	/* tries to transition
	220	0xffff0001 -> 0x00000000 */
	221	" jz 1f\n"
	222	" call call_rwsem_wake\n"
	223	"1:\n\t"
	224	"# ending __up_write\n"
59c33fa7 LT	225	: "+m" (sem->count), "=d" (tmp)
	226	: "a" (sem), "1" (-RWSEM_ACTIVE_WRITE_BIAS)
	227	: "memory", "cc");
1da177e4 LT	228	}
	229
	230	/*
	231	* downgrade write lock to read lock
	232	*/
	233	static inline void __downgrade_write(struct rw_semaphore *sem)
	234	{
6e5609a9	235	asm volatile("# beginning __downgrade_write\n\t"
1838ef1d	236	LOCK_PREFIX _ASM_ADD "%2,(%1)\n\t"
0d1622d7 AK	237	/*
	238	* transitions 0xZZZZ0001 -> 0xYYYY0001 (i386)
	239	* 0xZZZZZZZZ00000001 -> 0xYYYYYYYY00000001 (x86_64)
	240	*/
6e5609a9 JP	241	" jns 1f\n\t"
	242	" call call_rwsem_downgrade_wake\n"
	243	"1:\n\t"
	244	"# ending __downgrade_write\n"
	245	: "+m" (sem->count)
0d1622d7	246	: "a" (sem), "er" (-RWSEM_WAITING_BIAS)
6e5609a9	247	: "memory", "cc");
1da177e4 LT	248	}
	249
	250	/*
	251	* implement atomic add functionality
	252	*/
1838ef1d PA	253	static inline void rwsem_atomic_add(rwsem_count_t delta,
1838ef1d PA	254	struct rw_semaphore *sem)
1da177e4	255	{
1838ef1d	256	asm volatile(LOCK_PREFIX _ASM_ADD "%1,%0"
6e5609a9	257	: "+m" (sem->count)
1838ef1d	258	: "er" (delta));
1da177e4 LT	259	}
	260
	261	/*
	262	* implement exchange and add functionality
	263	*/
1838ef1d PA	264	static inline rwsem_count_t rwsem_atomic_update(rwsem_count_t delta,
1838ef1d PA	265	struct rw_semaphore *sem)
1da177e4	266	{
5d0b7235	267	rwsem_count_t tmp = delta;
1da177e4	268
6e5609a9 JP	269	asm volatile(LOCK_PREFIX "xadd %0,%1"
	270	: "+r" (tmp), "+m" (sem->count)
	271	: : "memory");
1da177e4	272
6e5609a9	273	return tmp + delta;
1da177e4 LT	274	}
1da177e4 LT	275
eb92f4ef RVR	276	static inline int rwsem_is_locked(struct rw_semaphore *sem)
	277	{
	278	return (sem->count != 0);
	279	}
	280
1da177e4	281	#endif /* __KERNEL__ */
1965aae3	282	#endif /* _ASM_X86_RWSEM_H */