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(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 once the synchronize_rcu() 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         /*
  51          * The preempt_enable() prevents the compiler from
  52          * bleeding the critical section out.
  53          */
  54         preempt_enable();
  55 }
  56
  57 static inline int percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
  58 {
  59         int ret = 1;
  60
  61         preempt_disable();
  62         /*
  63          * Same as in percpu_down_read().
  64          */
  65         __this_cpu_inc(*sem->read_count);
  66         if (unlikely(!rcu_sync_is_idle(&sem->rss)))
  67                 ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
  68         preempt_enable();
  69         /*
  70          * The barrier() from preempt_enable() prevents the compiler from
  71          * bleeding the critical section out.
  72          */
  73
  74         if (ret)
  75                 rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 1, _RET_IP_);
  76
  77         return ret;
  78 }
  79
  80 static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
  81 {
  82         preempt_disable();
  83         /*
  84          * Same as in percpu_down_read().
  85          */
  86         if (likely(rcu_sync_is_idle(&sem->rss)))
  87                 __this_cpu_dec(*sem->read_count);
  88         else
  89                 __percpu_up_read(sem); /* Unconditional memory barrier */
  90         preempt_enable();
  91
  92         rwsem_release(&sem->rw_sem.dep_map, 1, _RET_IP_);
  93 }
  94
  95 extern void percpu_down_write(struct percpu_rw_semaphore *);
  96 extern void percpu_up_write(struct percpu_rw_semaphore *);
  97
  98 extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
  99                                 const char *, struct lock_class_key *);
 100
 101 extern void percpu_free_rwsem(struct percpu_rw_semaphore *);
 102
 103 #define percpu_init_rwsem(sem)                                  \
 104 ({                                                              \
 105         static struct lock_class_key rwsem_key;                 \
 106         __percpu_init_rwsem(sem, #sem, &rwsem_key);             \
 107 })
 108
 109 #define percpu_rwsem_is_held(sem) lockdep_is_held(&(sem)->rw_sem)
 110
 111 #define percpu_rwsem_assert_held(sem)                           \
 112         lockdep_assert_held(&(sem)->rw_sem)
 113
 114 static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
 115                                         bool read, unsigned long ip)
 116 {
 117         lock_release(&sem->rw_sem.dep_map, 1, ip);
 118 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 119         if (!read)
 120                 sem->rw_sem.owner = RWSEM_OWNER_UNKNOWN;
 121 #endif
 122 }
 123
 124 static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
 125                                         bool read, unsigned long ip)
 126 {
 127         lock_acquire(&sem->rw_sem.dep_map, 0, 1, read, 1, NULL, ip);
 128 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 129         if (!read)
 130                 sem->rw_sem.owner = current;
 131 #endif
 132 }
 133
 134 #endif