include/linux/percpu-rwsem.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _LINUX_PERCPU_RWSEM_H
   3 #define _LINUX_PERCPU_RWSEM_H
   4
   5 #include <linux/atomic.h>
   6 #include <linux/rwsem.h>
   7 #include <linux/percpu.h>
   8 #include <linux/rcuwait.h>
   9 #include <linux/rcu_sync.h>
  10 #include <linux/lockdep.h>
  11
  12 struct percpu_rw_semaphore {
  13         struct rcu_sync         rss;
  14         unsigned int __percpu   *read_count;
  15         struct rw_semaphore     rw_sem; /* slowpath */
  16         struct rcuwait          writer; /* blocked writer */
  17         int                     readers_block;
  18 };
  19
  20 #define DEFINE_STATIC_PERCPU_RWSEM(name)                                \
  21 static DEFINE_PER_CPU(unsigned int, __percpu_rwsem_rc_##name);          \
  22 static struct percpu_rw_semaphore name = {                              \
  23         .rss = __RCU_SYNC_INITIALIZER(name.rss, RCU_SCHED_SYNC),        \
  24         .read_count = &__percpu_rwsem_rc_##name,                        \
  25         .rw_sem = __RWSEM_INITIALIZER(name.rw_sem),                     \
  26         .writer = __RCUWAIT_INITIALIZER(name.writer),                   \
  27 }
  28
  29 extern int __percpu_down_read(struct percpu_rw_semaphore *, int);
  30 extern void __percpu_up_read(struct percpu_rw_semaphore *);
  31
  32 static inline void percpu_down_read_preempt_disable(struct percpu_rw_semaphore *sem)
  33 {
  34         might_sleep();
  35
  36         rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 0, _RET_IP_);
  37
  38         preempt_disable();
  39         /*
  40          * We are in an RCU-sched read-side critical section, so the writer
  41          * cannot both change sem->state from readers_fast and start checking
  42          * counters while we are here. So if we see !sem->state, we know that
  43          * the writer won't be checking until we're past the preempt_enable()
  44          * and that one the synchronize_sched() is done, the writer will see
  45          * anything we did within this RCU-sched read-size critical section.
  46          */
  47         __this_cpu_inc(*sem->read_count);
  48         if (unlikely(!rcu_sync_is_idle(&sem->rss)))
  49                 __percpu_down_read(sem, false); /* Unconditional memory barrier */
  50         barrier();
  51         /*
  52          * The barrier() prevents the compiler from
  53          * bleeding the critical section out.
  54          */
  55 }
  56
  57 static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
  58 {
  59         percpu_down_read_preempt_disable(sem);
  60         preempt_enable();
  61 }
  62
  63 static inline int percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
  64 {
  65         int ret = 1;
  66
  67         preempt_disable();
  68         /*
  69          * Same as in percpu_down_read().
  70          */
  71         __this_cpu_inc(*sem->read_count);
  72         if (unlikely(!rcu_sync_is_idle(&sem->rss)))
  73                 ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
  74         preempt_enable();
  75         /*
  76          * The barrier() from preempt_enable() prevents the compiler from
  77          * bleeding the critical section out.
  78          */
  79
  80         if (ret)
  81                 rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 1, _RET_IP_);
  82
  83         return ret;
  84 }
  85
  86 static inline void percpu_up_read_preempt_enable(struct percpu_rw_semaphore *sem)
  87 {
  88         /*
  89          * The barrier() prevents the compiler from
  90          * bleeding the critical section out.
  91          */
  92         barrier();
  93         /*
  94          * Same as in percpu_down_read().
  95          */
  96         if (likely(rcu_sync_is_idle(&sem->rss)))
  97                 __this_cpu_dec(*sem->read_count);
  98         else
  99                 __percpu_up_read(sem); /* Unconditional memory barrier */
 100         preempt_enable();
 101
 102         rwsem_release(&sem->rw_sem.dep_map, 1, _RET_IP_);
 103 }
 104
 105 static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
 106 {
 107         preempt_disable();
 108         percpu_up_read_preempt_enable(sem);
 109 }
 110
 111 extern void percpu_down_write(struct percpu_rw_semaphore *);
 112 extern void percpu_up_write(struct percpu_rw_semaphore *);
 113
 114 extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
 115                                 const char *, struct lock_class_key *);
 116
 117 extern void percpu_free_rwsem(struct percpu_rw_semaphore *);
 118
 119 #define percpu_init_rwsem(sem)                                  \
 120 ({                                                              \
 121         static struct lock_class_key rwsem_key;                 \
 122         __percpu_init_rwsem(sem, #sem, &rwsem_key);             \
 123 })
 124
 125 #define percpu_rwsem_is_held(sem) lockdep_is_held(&(sem)->rw_sem)
 126
 127 #define percpu_rwsem_assert_held(sem)                           \
 128         lockdep_assert_held(&(sem)->rw_sem)
 129
 130 static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
 131                                         bool read, unsigned long ip)
 132 {
 133         lock_release(&sem->rw_sem.dep_map, 1, ip);
 134 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 135         if (!read)
 136                 sem->rw_sem.owner = NULL;
 137 #endif
 138 }
 139
 140 static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
 141                                         bool read, unsigned long ip)
 142 {
 143         lock_acquire(&sem->rw_sem.dep_map, 0, 1, read, 1, NULL, ip);
 144 }
 145
 146 #endif