include/linux/percpu-rwsem.h

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