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 /*
  28  * __might_resched() skips the state check as rtlocks are state
  29  * preserving. Take RCU nesting into account as spin/read/write_lock() can
  30  * legitimately nest into an RCU read side critical section.
  31  */
  32 #define RTLOCK_RESCHED_OFFSETS                                          \
  33         (rcu_preempt_depth() << MIGHT_RESCHED_RCU_SHIFT)
  34
  35 #define rtlock_might_resched()                                          \
  36         __might_resched(__FILE__, __LINE__, RTLOCK_RESCHED_OFFSETS)
  37
  38 static __always_inline void rtlock_lock(struct rt_mutex_base *rtm)
  39 {
  40         if (unlikely(!rt_mutex_cmpxchg_acquire(rtm, NULL, current)))
  41                 rtlock_slowlock(rtm);
  42 }
  43
  44 static __always_inline void __rt_spin_lock(spinlock_t *lock)
  45 {
  46         rtlock_might_resched();
  47         rtlock_lock(&lock->lock);
  48         rcu_read_lock();
  49         migrate_disable();
  50 }
  51
  52 void __sched rt_spin_lock(spinlock_t *lock)
  53 {
  54         spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
  55         __rt_spin_lock(lock);
  56 }
  57 EXPORT_SYMBOL(rt_spin_lock);
  58
  59 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  60 void __sched rt_spin_lock_nested(spinlock_t *lock, int subclass)
  61 {
  62         spin_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
  63         __rt_spin_lock(lock);
  64 }
  65 EXPORT_SYMBOL(rt_spin_lock_nested);
  66
  67 void __sched rt_spin_lock_nest_lock(spinlock_t *lock,
  68                                     struct lockdep_map *nest_lock)
  69 {
  70         spin_acquire_nest(&lock->dep_map, 0, 0, nest_lock, _RET_IP_);
  71         __rt_spin_lock(lock);
  72 }
  73 EXPORT_SYMBOL(rt_spin_lock_nest_lock);
  74 #endif
  75
  76 void __sched rt_spin_unlock(spinlock_t *lock)
  77 {
  78         spin_release(&lock->dep_map, _RET_IP_);
  79         migrate_enable();
  80         rcu_read_unlock();
  81
  82         if (unlikely(!rt_mutex_cmpxchg_release(&lock->lock, current, NULL)))
  83                 rt_mutex_slowunlock(&lock->lock);
  84 }
  85 EXPORT_SYMBOL(rt_spin_unlock);
  86
  87 /*
  88  * Wait for the lock to get unlocked: instead of polling for an unlock
  89  * (like raw spinlocks do), lock and unlock, to force the kernel to
  90  * schedule if there's contention:
  91  */
  92 void __sched rt_spin_lock_unlock(spinlock_t *lock)
  93 {
  94         spin_lock(lock);
  95         spin_unlock(lock);
  96 }
  97 EXPORT_SYMBOL(rt_spin_lock_unlock);
  98
  99 static __always_inline int __rt_spin_trylock(spinlock_t *lock)
 100 {
 101         int ret = 1;
 102
 103         if (unlikely(!rt_mutex_cmpxchg_acquire(&lock->lock, NULL, current)))
 104                 ret = rt_mutex_slowtrylock(&lock->lock);
 105
 106         if (ret) {
 107                 spin_acquire(&lock->dep_map, 0, 1, _RET_IP_);
 108                 rcu_read_lock();
 109                 migrate_disable();
 110         }
 111         return ret;
 112 }
 113
 114 int __sched rt_spin_trylock(spinlock_t *lock)
 115 {
 116         return __rt_spin_trylock(lock);
 117 }
 118 EXPORT_SYMBOL(rt_spin_trylock);
 119
 120 int __sched rt_spin_trylock_bh(spinlock_t *lock)
 121 {
 122         int ret;
 123
 124         local_bh_disable();
 125         ret = __rt_spin_trylock(lock);
 126         if (!ret)
 127                 local_bh_enable();
 128         return ret;
 129 }
 130 EXPORT_SYMBOL(rt_spin_trylock_bh);
 131
 132 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 133 void __rt_spin_lock_init(spinlock_t *lock, const char *name,
 134                          struct lock_class_key *key, bool percpu)
 135 {
 136         u8 type = percpu ? LD_LOCK_PERCPU : LD_LOCK_NORMAL;
 137
 138         debug_check_no_locks_freed((void *)lock, sizeof(*lock));
 139         lockdep_init_map_type(&lock->dep_map, name, key, 0, LD_WAIT_CONFIG,
 140                               LD_WAIT_INV, type);
 141 }
 142 EXPORT_SYMBOL(__rt_spin_lock_init);
 143 #endif
 144
 145 /*
 146  * RT-specific reader/writer locks
 147  */
 148 #define rwbase_set_and_save_current_state(state)        \
 149         current_save_and_set_rtlock_wait_state()
 150
 151 #define rwbase_restore_current_state()                  \
 152         current_restore_rtlock_saved_state()
 153
 154 static __always_inline int
 155 rwbase_rtmutex_lock_state(struct rt_mutex_base *rtm, unsigned int state)
 156 {
 157         if (unlikely(!rt_mutex_cmpxchg_acquire(rtm, NULL, current)))
 158                 rtlock_slowlock(rtm);
 159         return 0;
 160 }
 161
 162 static __always_inline int
 163 rwbase_rtmutex_slowlock_locked(struct rt_mutex_base *rtm, unsigned int state)
 164 {
 165         rtlock_slowlock_locked(rtm);
 166         return 0;
 167 }
 168
 169 static __always_inline void rwbase_rtmutex_unlock(struct rt_mutex_base *rtm)
 170 {
 171         if (likely(rt_mutex_cmpxchg_acquire(rtm, current, NULL)))
 172                 return;
 173
 174         rt_mutex_slowunlock(rtm);
 175 }
 176
 177 static __always_inline int  rwbase_rtmutex_trylock(struct rt_mutex_base *rtm)
 178 {
 179         if (likely(rt_mutex_cmpxchg_acquire(rtm, NULL, current)))
 180                 return 1;
 181
 182         return rt_mutex_slowtrylock(rtm);
 183 }
 184
 185 #define rwbase_signal_pending_state(state, current)     (0)
 186
 187 #define rwbase_schedule()                               \
 188         schedule_rtlock()
 189
 190 #include "rwbase_rt.c"
 191 /*
 192  * The common functions which get wrapped into the rwlock API.
 193  */
 194 int __sched rt_read_trylock(rwlock_t *rwlock)
 195 {
 196         int ret;
 197
 198         ret = rwbase_read_trylock(&rwlock->rwbase);
 199         if (ret) {
 200                 rwlock_acquire_read(&rwlock->dep_map, 0, 1, _RET_IP_);
 201                 rcu_read_lock();
 202                 migrate_disable();
 203         }
 204         return ret;
 205 }
 206 EXPORT_SYMBOL(rt_read_trylock);
 207
 208 int __sched rt_write_trylock(rwlock_t *rwlock)
 209 {
 210         int ret;
 211
 212         ret = rwbase_write_trylock(&rwlock->rwbase);
 213         if (ret) {
 214                 rwlock_acquire(&rwlock->dep_map, 0, 1, _RET_IP_);
 215                 rcu_read_lock();
 216                 migrate_disable();
 217         }
 218         return ret;
 219 }
 220 EXPORT_SYMBOL(rt_write_trylock);
 221
 222 void __sched rt_read_lock(rwlock_t *rwlock)
 223 {
 224         rtlock_might_resched();
 225         rwlock_acquire_read(&rwlock->dep_map, 0, 0, _RET_IP_);
 226         rwbase_read_lock(&rwlock->rwbase, TASK_RTLOCK_WAIT);
 227         rcu_read_lock();
 228         migrate_disable();
 229 }
 230 EXPORT_SYMBOL(rt_read_lock);
 231
 232 void __sched rt_write_lock(rwlock_t *rwlock)
 233 {
 234         rtlock_might_resched();
 235         rwlock_acquire(&rwlock->dep_map, 0, 0, _RET_IP_);
 236         rwbase_write_lock(&rwlock->rwbase, TASK_RTLOCK_WAIT);
 237         rcu_read_lock();
 238         migrate_disable();
 239 }
 240 EXPORT_SYMBOL(rt_write_lock);
 241
 242 void __sched rt_read_unlock(rwlock_t *rwlock)
 243 {
 244         rwlock_release(&rwlock->dep_map, _RET_IP_);
 245         migrate_enable();
 246         rcu_read_unlock();
 247         rwbase_read_unlock(&rwlock->rwbase, TASK_RTLOCK_WAIT);
 248 }
 249 EXPORT_SYMBOL(rt_read_unlock);
 250
 251 void __sched rt_write_unlock(rwlock_t *rwlock)
 252 {
 253         rwlock_release(&rwlock->dep_map, _RET_IP_);
 254         rcu_read_unlock();
 255         migrate_enable();
 256         rwbase_write_unlock(&rwlock->rwbase);
 257 }
 258 EXPORT_SYMBOL(rt_write_unlock);
 259
 260 int __sched rt_rwlock_is_contended(rwlock_t *rwlock)
 261 {
 262         return rw_base_is_contended(&rwlock->rwbase);
 263 }
 264 EXPORT_SYMBOL(rt_rwlock_is_contended);
 265
 266 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 267 void __rt_rwlock_init(rwlock_t *rwlock, const char *name,
 268                       struct lock_class_key *key)
 269 {
 270         debug_check_no_locks_freed((void *)rwlock, sizeof(*rwlock));
 271         lockdep_init_map_wait(&rwlock->dep_map, name, key, 0, LD_WAIT_CONFIG);
 272 }
 273 EXPORT_SYMBOL(__rt_rwlock_init);
 274 #endif