1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * PREEMPT_RT substitution for spin/rw_locks 4 * 5 * spinlocks and rwlocks on RT are based on rtmutexes, with a few twists to 6 * resemble the non RT semantics: 7 * 8 * - Contrary to plain rtmutexes, spinlocks and rwlocks are state 9 * preserving. The task state is saved before blocking on the underlying 10 * rtmutex, and restored when the lock has been acquired. Regular wakeups 11 * during that time are redirected to the saved state so no wake up is 12 * missed. 13 * 14 * - Non RT spin/rwlocks disable preemption and eventually interrupts. 15 * Disabling preemption has the side effect of disabling migration and 16 * preventing RCU grace periods. 17 * 18 * The RT substitutions explicitly disable migration and take 19 * rcu_read_lock() across the lock held section. 20 */ 21 #include <linux/spinlock.h> 22 #include <linux/export.h> 23 24 #define RT_MUTEX_BUILD_SPINLOCKS 25 #include "rtmutex.c" 26 27 static __always_inline void rtlock_lock(struct rt_mutex_base *rtm) 28 { 29 if (unlikely(!rt_mutex_cmpxchg_acquire(rtm, NULL, current))) 30 rtlock_slowlock(rtm); 31 } 32 33 static __always_inline void __rt_spin_lock(spinlock_t *lock) 34 { 35 ___might_sleep(__FILE__, __LINE__, 0); 36 rtlock_lock(&lock->lock); 37 rcu_read_lock(); 38 migrate_disable(); 39 } 40 41 void __sched rt_spin_lock(spinlock_t *lock) 42 { 43 spin_acquire(&lock->dep_map, 0, 0, _RET_IP_); 44 __rt_spin_lock(lock); 45 } 46 EXPORT_SYMBOL(rt_spin_lock); 47 48 #ifdef CONFIG_DEBUG_LOCK_ALLOC 49 void __sched rt_spin_lock_nested(spinlock_t *lock, int subclass) 50 { 51 spin_acquire(&lock->dep_map, subclass, 0, _RET_IP_); 52 __rt_spin_lock(lock); 53 } 54 EXPORT_SYMBOL(rt_spin_lock_nested); 55 56 void __sched rt_spin_lock_nest_lock(spinlock_t *lock, 57 struct lockdep_map *nest_lock) 58 { 59 spin_acquire_nest(&lock->dep_map, 0, 0, nest_lock, _RET_IP_); 60 __rt_spin_lock(lock); 61 } 62 EXPORT_SYMBOL(rt_spin_lock_nest_lock); 63 #endif 64 65 void __sched rt_spin_unlock(spinlock_t *lock) 66 { 67 spin_release(&lock->dep_map, _RET_IP_); 68 migrate_enable(); 69 rcu_read_unlock(); 70 71 if (unlikely(!rt_mutex_cmpxchg_release(&lock->lock, current, NULL))) 72 rt_mutex_slowunlock(&lock->lock); 73 } 74 EXPORT_SYMBOL(rt_spin_unlock); 75 76 /* 77 * Wait for the lock to get unlocked: instead of polling for an unlock 78 * (like raw spinlocks do), lock and unlock, to force the kernel to 79 * schedule if there's contention: 80 */ 81 void __sched rt_spin_lock_unlock(spinlock_t *lock) 82 { 83 spin_lock(lock); 84 spin_unlock(lock); 85 } 86 EXPORT_SYMBOL(rt_spin_lock_unlock); 87 88 static __always_inline int __rt_spin_trylock(spinlock_t *lock) 89 { 90 int ret = 1; 91 92 if (unlikely(!rt_mutex_cmpxchg_acquire(&lock->lock, NULL, current))) 93 ret = rt_mutex_slowtrylock(&lock->lock); 94 95 if (ret) { 96 spin_acquire(&lock->dep_map, 0, 1, _RET_IP_); 97 rcu_read_lock(); 98 migrate_disable(); 99 } 100 return ret; 101 } 102 103 int __sched rt_spin_trylock(spinlock_t *lock) 104 { 105 return __rt_spin_trylock(lock); 106 } 107 EXPORT_SYMBOL(rt_spin_trylock); 108 109 int __sched rt_spin_trylock_bh(spinlock_t *lock) 110 { 111 int ret; 112 113 local_bh_disable(); 114 ret = __rt_spin_trylock(lock); 115 if (!ret) 116 local_bh_enable(); 117 return ret; 118 } 119 EXPORT_SYMBOL(rt_spin_trylock_bh); 120 121 #ifdef CONFIG_DEBUG_LOCK_ALLOC 122 void __rt_spin_lock_init(spinlock_t *lock, const char *name, 123 struct lock_class_key *key) 124 { 125 debug_check_no_locks_freed((void *)lock, sizeof(*lock)); 126 lockdep_init_map_wait(&lock->dep_map, name, key, 0, LD_WAIT_CONFIG); 127 } 128 EXPORT_SYMBOL(__rt_spin_lock_init); 129 #endif 130 131 /* 132 * RT-specific reader/writer locks 133 */ 134 #define rwbase_set_and_save_current_state(state) \ 135 current_save_and_set_rtlock_wait_state() 136 137 #define rwbase_restore_current_state() \ 138 current_restore_rtlock_saved_state() 139 140 static __always_inline int 141 rwbase_rtmutex_lock_state(struct rt_mutex_base *rtm, unsigned int state) 142 { 143 if (unlikely(!rt_mutex_cmpxchg_acquire(rtm, NULL, current))) 144 rtlock_slowlock(rtm); 145 return 0; 146 } 147 148 static __always_inline int 149 rwbase_rtmutex_slowlock_locked(struct rt_mutex_base *rtm, unsigned int state) 150 { 151 rtlock_slowlock_locked(rtm); 152 return 0; 153 } 154 155 static __always_inline void rwbase_rtmutex_unlock(struct rt_mutex_base *rtm) 156 { 157 if (likely(rt_mutex_cmpxchg_acquire(rtm, current, NULL))) 158 return; 159 160 rt_mutex_slowunlock(rtm); 161 } 162 163 static __always_inline int rwbase_rtmutex_trylock(struct rt_mutex_base *rtm) 164 { 165 if (likely(rt_mutex_cmpxchg_acquire(rtm, NULL, current))) 166 return 1; 167 168 return rt_mutex_slowtrylock(rtm); 169 } 170 171 #define rwbase_signal_pending_state(state, current) (0) 172 173 #define rwbase_schedule() \ 174 schedule_rtlock() 175 176 #include "rwbase_rt.c" 177 /* 178 * The common functions which get wrapped into the rwlock API. 179 */ 180 int __sched rt_read_trylock(rwlock_t *rwlock) 181 { 182 int ret; 183 184 ret = rwbase_read_trylock(&rwlock->rwbase); 185 if (ret) { 186 rwlock_acquire_read(&rwlock->dep_map, 0, 1, _RET_IP_); 187 rcu_read_lock(); 188 migrate_disable(); 189 } 190 return ret; 191 } 192 EXPORT_SYMBOL(rt_read_trylock); 193 194 int __sched rt_write_trylock(rwlock_t *rwlock) 195 { 196 int ret; 197 198 ret = rwbase_write_trylock(&rwlock->rwbase); 199 if (ret) { 200 rwlock_acquire(&rwlock->dep_map, 0, 1, _RET_IP_); 201 rcu_read_lock(); 202 migrate_disable(); 203 } 204 return ret; 205 } 206 EXPORT_SYMBOL(rt_write_trylock); 207 208 void __sched rt_read_lock(rwlock_t *rwlock) 209 { 210 ___might_sleep(__FILE__, __LINE__, 0); 211 rwlock_acquire_read(&rwlock->dep_map, 0, 0, _RET_IP_); 212 rwbase_read_lock(&rwlock->rwbase, TASK_RTLOCK_WAIT); 213 rcu_read_lock(); 214 migrate_disable(); 215 } 216 EXPORT_SYMBOL(rt_read_lock); 217 218 void __sched rt_write_lock(rwlock_t *rwlock) 219 { 220 ___might_sleep(__FILE__, __LINE__, 0); 221 rwlock_acquire(&rwlock->dep_map, 0, 0, _RET_IP_); 222 rwbase_write_lock(&rwlock->rwbase, TASK_RTLOCK_WAIT); 223 rcu_read_lock(); 224 migrate_disable(); 225 } 226 EXPORT_SYMBOL(rt_write_lock); 227 228 void __sched rt_read_unlock(rwlock_t *rwlock) 229 { 230 rwlock_release(&rwlock->dep_map, _RET_IP_); 231 migrate_enable(); 232 rcu_read_unlock(); 233 rwbase_read_unlock(&rwlock->rwbase, TASK_RTLOCK_WAIT); 234 } 235 EXPORT_SYMBOL(rt_read_unlock); 236 237 void __sched rt_write_unlock(rwlock_t *rwlock) 238 { 239 rwlock_release(&rwlock->dep_map, _RET_IP_); 240 rcu_read_unlock(); 241 migrate_enable(); 242 rwbase_write_unlock(&rwlock->rwbase); 243 } 244 EXPORT_SYMBOL(rt_write_unlock); 245 246 int __sched rt_rwlock_is_contended(rwlock_t *rwlock) 247 { 248 return rw_base_is_contended(&rwlock->rwbase); 249 } 250 EXPORT_SYMBOL(rt_rwlock_is_contended); 251 252 #ifdef CONFIG_DEBUG_LOCK_ALLOC 253 void __rt_rwlock_init(rwlock_t *rwlock, const char *name, 254 struct lock_class_key *key) 255 { 256 debug_check_no_locks_freed((void *)rwlock, sizeof(*rwlock)); 257 lockdep_init_map_wait(&rwlock->dep_map, name, key, 0, LD_WAIT_CONFIG); 258 } 259 EXPORT_SYMBOL(__rt_rwlock_init); 260 #endif 261