Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | /* rwsem.h: R/W semaphores implemented using XADD/CMPXCHG for i486+ |
| 2 | * |
| 3 | * Written by David Howells (dhowells@redhat.com). |
| 4 | * |
Dave Jones | 99122a3 | 2008-01-30 13:30:28 +0100 | [diff] [blame] | 5 | * Derived from asm-x86/semaphore.h |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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 | |
| 32 | #ifndef _I386_RWSEM_H |
| 33 | #define _I386_RWSEM_H |
| 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> |
Ingo Molnar | 4ea2176 | 2006-07-03 00:24:53 -0700 | [diff] [blame] | 43 | #include <linux/lockdep.h> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 44 | |
| 45 | struct rwsem_waiter; |
| 46 | |
Ingo Molnar | d50efc6 | 2008-01-30 13:33:00 +0100 | [diff] [blame] | 47 | extern asmregparm struct rw_semaphore * |
| 48 | rwsem_down_read_failed(struct rw_semaphore *sem); |
| 49 | extern asmregparm struct rw_semaphore * |
| 50 | rwsem_down_write_failed(struct rw_semaphore *sem); |
| 51 | extern asmregparm struct rw_semaphore * |
| 52 | rwsem_wake(struct rw_semaphore *); |
| 53 | extern asmregparm struct rw_semaphore * |
| 54 | rwsem_downgrade_wake(struct rw_semaphore *sem); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 55 | |
| 56 | /* |
| 57 | * the semaphore definition |
| 58 | */ |
| 59 | struct rw_semaphore { |
| 60 | signed long count; |
| 61 | #define RWSEM_UNLOCKED_VALUE 0x00000000 |
| 62 | #define RWSEM_ACTIVE_BIAS 0x00000001 |
| 63 | #define RWSEM_ACTIVE_MASK 0x0000ffff |
| 64 | #define RWSEM_WAITING_BIAS (-0x00010000) |
| 65 | #define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS |
| 66 | #define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS) |
| 67 | spinlock_t wait_lock; |
| 68 | struct list_head wait_list; |
Ingo Molnar | 4ea2176 | 2006-07-03 00:24:53 -0700 | [diff] [blame] | 69 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
| 70 | struct lockdep_map dep_map; |
| 71 | #endif |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 72 | }; |
| 73 | |
Ingo Molnar | 4ea2176 | 2006-07-03 00:24:53 -0700 | [diff] [blame] | 74 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
| 75 | # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname } |
| 76 | #else |
| 77 | # define __RWSEM_DEP_MAP_INIT(lockname) |
| 78 | #endif |
| 79 | |
| 80 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 81 | #define __RWSEM_INITIALIZER(name) \ |
Peter Zijlstra | 6cfd76a | 2006-12-06 20:37:22 -0800 | [diff] [blame] | 82 | { RWSEM_UNLOCKED_VALUE, __SPIN_LOCK_UNLOCKED((name).wait_lock), \ |
| 83 | LIST_HEAD_INIT((name).wait_list) __RWSEM_DEP_MAP_INIT(name) } |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 84 | |
| 85 | #define DECLARE_RWSEM(name) \ |
| 86 | struct rw_semaphore name = __RWSEM_INITIALIZER(name) |
| 87 | |
Ingo Molnar | 4ea2176 | 2006-07-03 00:24:53 -0700 | [diff] [blame] | 88 | extern void __init_rwsem(struct rw_semaphore *sem, const char *name, |
| 89 | struct lock_class_key *key); |
| 90 | |
| 91 | #define init_rwsem(sem) \ |
| 92 | do { \ |
| 93 | static struct lock_class_key __key; \ |
| 94 | \ |
| 95 | __init_rwsem((sem), #sem, &__key); \ |
| 96 | } while (0) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 97 | |
| 98 | /* |
| 99 | * lock for reading |
| 100 | */ |
| 101 | static inline void __down_read(struct rw_semaphore *sem) |
| 102 | { |
| 103 | __asm__ __volatile__( |
| 104 | "# beginning down_read\n\t" |
| 105 | LOCK_PREFIX " incl (%%eax)\n\t" /* adds 0x00000001, returns the old value */ |
Andi Kleen | add659b | 2006-09-26 10:52:31 +0200 | [diff] [blame] | 106 | " jns 1f\n" |
| 107 | " call call_rwsem_down_read_failed\n" |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 108 | "1:\n\t" |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 109 | "# ending down_read\n\t" |
Linus Torvalds | b862f3b | 2006-07-08 15:24:18 -0700 | [diff] [blame] | 110 | : "+m" (sem->count) |
| 111 | : "a" (sem) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 112 | : "memory", "cc"); |
| 113 | } |
| 114 | |
| 115 | /* |
| 116 | * trylock for reading -- returns 1 if successful, 0 if contention |
| 117 | */ |
| 118 | static inline int __down_read_trylock(struct rw_semaphore *sem) |
| 119 | { |
| 120 | __s32 result, tmp; |
| 121 | __asm__ __volatile__( |
| 122 | "# beginning __down_read_trylock\n\t" |
| 123 | " movl %0,%1\n\t" |
| 124 | "1:\n\t" |
| 125 | " movl %1,%2\n\t" |
| 126 | " addl %3,%2\n\t" |
| 127 | " jle 2f\n\t" |
| 128 | LOCK_PREFIX " cmpxchgl %2,%0\n\t" |
| 129 | " jnz 1b\n\t" |
| 130 | "2:\n\t" |
| 131 | "# ending __down_read_trylock\n\t" |
Linus Torvalds | b862f3b | 2006-07-08 15:24:18 -0700 | [diff] [blame] | 132 | : "+m" (sem->count), "=&a" (result), "=&r" (tmp) |
| 133 | : "i" (RWSEM_ACTIVE_READ_BIAS) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 134 | : "memory", "cc"); |
| 135 | return result>=0 ? 1 : 0; |
| 136 | } |
| 137 | |
| 138 | /* |
| 139 | * lock for writing |
| 140 | */ |
Ingo Molnar | 4ea2176 | 2006-07-03 00:24:53 -0700 | [diff] [blame] | 141 | static inline void __down_write_nested(struct rw_semaphore *sem, int subclass) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 142 | { |
| 143 | int tmp; |
| 144 | |
| 145 | tmp = RWSEM_ACTIVE_WRITE_BIAS; |
| 146 | __asm__ __volatile__( |
| 147 | "# beginning down_write\n\t" |
| 148 | LOCK_PREFIX " xadd %%edx,(%%eax)\n\t" /* subtract 0x0000ffff, returns the old value */ |
| 149 | " testl %%edx,%%edx\n\t" /* was the count 0 before? */ |
Andi Kleen | add659b | 2006-09-26 10:52:31 +0200 | [diff] [blame] | 150 | " jz 1f\n" |
| 151 | " call call_rwsem_down_write_failed\n" |
| 152 | "1:\n" |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 153 | "# ending down_write" |
Linus Torvalds | b862f3b | 2006-07-08 15:24:18 -0700 | [diff] [blame] | 154 | : "+m" (sem->count), "=d" (tmp) |
| 155 | : "a" (sem), "1" (tmp) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 156 | : "memory", "cc"); |
| 157 | } |
| 158 | |
Ingo Molnar | 4ea2176 | 2006-07-03 00:24:53 -0700 | [diff] [blame] | 159 | static inline void __down_write(struct rw_semaphore *sem) |
| 160 | { |
| 161 | __down_write_nested(sem, 0); |
| 162 | } |
| 163 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 164 | /* |
| 165 | * trylock for writing -- returns 1 if successful, 0 if contention |
| 166 | */ |
| 167 | static inline int __down_write_trylock(struct rw_semaphore *sem) |
| 168 | { |
| 169 | signed long ret = cmpxchg(&sem->count, |
| 170 | RWSEM_UNLOCKED_VALUE, |
| 171 | RWSEM_ACTIVE_WRITE_BIAS); |
| 172 | if (ret == RWSEM_UNLOCKED_VALUE) |
| 173 | return 1; |
| 174 | return 0; |
| 175 | } |
| 176 | |
| 177 | /* |
| 178 | * unlock after reading |
| 179 | */ |
| 180 | static inline void __up_read(struct rw_semaphore *sem) |
| 181 | { |
| 182 | __s32 tmp = -RWSEM_ACTIVE_READ_BIAS; |
| 183 | __asm__ __volatile__( |
| 184 | "# beginning __up_read\n\t" |
| 185 | LOCK_PREFIX " xadd %%edx,(%%eax)\n\t" /* subtracts 1, returns the old value */ |
Andi Kleen | add659b | 2006-09-26 10:52:31 +0200 | [diff] [blame] | 186 | " jns 1f\n\t" |
| 187 | " call call_rwsem_wake\n" |
| 188 | "1:\n" |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 189 | "# ending __up_read\n" |
Linus Torvalds | b862f3b | 2006-07-08 15:24:18 -0700 | [diff] [blame] | 190 | : "+m" (sem->count), "=d" (tmp) |
| 191 | : "a" (sem), "1" (tmp) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 192 | : "memory", "cc"); |
| 193 | } |
| 194 | |
| 195 | /* |
| 196 | * unlock after writing |
| 197 | */ |
| 198 | static inline void __up_write(struct rw_semaphore *sem) |
| 199 | { |
| 200 | __asm__ __volatile__( |
| 201 | "# beginning __up_write\n\t" |
| 202 | " movl %2,%%edx\n\t" |
| 203 | LOCK_PREFIX " xaddl %%edx,(%%eax)\n\t" /* tries to transition 0xffff0001 -> 0x00000000 */ |
Andi Kleen | add659b | 2006-09-26 10:52:31 +0200 | [diff] [blame] | 204 | " jz 1f\n" |
| 205 | " call call_rwsem_wake\n" |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 206 | "1:\n\t" |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 207 | "# ending __up_write\n" |
Linus Torvalds | b862f3b | 2006-07-08 15:24:18 -0700 | [diff] [blame] | 208 | : "+m" (sem->count) |
| 209 | : "a" (sem), "i" (-RWSEM_ACTIVE_WRITE_BIAS) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 210 | : "memory", "cc", "edx"); |
| 211 | } |
| 212 | |
| 213 | /* |
| 214 | * downgrade write lock to read lock |
| 215 | */ |
| 216 | static inline void __downgrade_write(struct rw_semaphore *sem) |
| 217 | { |
| 218 | __asm__ __volatile__( |
| 219 | "# beginning __downgrade_write\n\t" |
| 220 | LOCK_PREFIX " addl %2,(%%eax)\n\t" /* transitions 0xZZZZ0001 -> 0xYYYY0001 */ |
Andi Kleen | add659b | 2006-09-26 10:52:31 +0200 | [diff] [blame] | 221 | " jns 1f\n\t" |
| 222 | " call call_rwsem_downgrade_wake\n" |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 223 | "1:\n\t" |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 224 | "# ending __downgrade_write\n" |
Linus Torvalds | b862f3b | 2006-07-08 15:24:18 -0700 | [diff] [blame] | 225 | : "+m" (sem->count) |
| 226 | : "a" (sem), "i" (-RWSEM_WAITING_BIAS) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 227 | : "memory", "cc"); |
| 228 | } |
| 229 | |
| 230 | /* |
| 231 | * implement atomic add functionality |
| 232 | */ |
| 233 | static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem) |
| 234 | { |
| 235 | __asm__ __volatile__( |
| 236 | LOCK_PREFIX "addl %1,%0" |
Linus Torvalds | b862f3b | 2006-07-08 15:24:18 -0700 | [diff] [blame] | 237 | : "+m" (sem->count) |
| 238 | : "ir" (delta)); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 239 | } |
| 240 | |
| 241 | /* |
| 242 | * implement exchange and add functionality |
| 243 | */ |
| 244 | static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem) |
| 245 | { |
| 246 | int tmp = delta; |
| 247 | |
| 248 | __asm__ __volatile__( |
Linus Torvalds | b862f3b | 2006-07-08 15:24:18 -0700 | [diff] [blame] | 249 | LOCK_PREFIX "xadd %0,%1" |
| 250 | : "+r" (tmp), "+m" (sem->count) |
| 251 | : : "memory"); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 252 | |
| 253 | return tmp+delta; |
| 254 | } |
| 255 | |
Rik Van Riel | eb92f4e | 2005-10-29 18:15:44 -0700 | [diff] [blame] | 256 | static inline int rwsem_is_locked(struct rw_semaphore *sem) |
| 257 | { |
| 258 | return (sem->count != 0); |
| 259 | } |
| 260 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 261 | #endif /* __KERNEL__ */ |
| 262 | #endif /* _I386_RWSEM_H */ |