LXR linux/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
  11struct 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)                                \
  20static DEFINE_PER_CPU(unsigned int, __percpu_rwsem_rc_##name);          \
  21static 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
  28extern int __percpu_down_read(struct percpu_rw_semaphore *, int);
  29extern void __percpu_up_read(struct percpu_rw_semaphore *);
  30
  31static 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
  56static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
  57{
  58        percpu_down_read_preempt_disable(sem);
  59        preempt_enable();
  60}
  61
  62static 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
  85static 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
 104static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
 105{
 106        preempt_disable();
 107        percpu_up_read_preempt_enable(sem);
 108}
 109
 110extern void percpu_down_write(struct percpu_rw_semaphore *);
 111extern void percpu_up_write(struct percpu_rw_semaphore *);
 112
 113extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
 114                                const char *, struct lock_class_key *);
 115
 116extern 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
 129static 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
 139static 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
 146