kernel/locking/spinlock_rt.c

   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