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