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/wait.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;
  15         wait_queue_head_t       writer;
  16         int                     readers_block;
  17 };
  18
  19 extern int __percpu_down_read(struct percpu_rw_semaphore *, int);
  20 extern void __percpu_up_read(struct percpu_rw_semaphore *);
  21
  22 static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
  23 {
  24         might_sleep();
  25
  26         rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 0, _RET_IP_);
  27
  28         preempt_disable();
  29         /*
  30          * We are in an RCU-sched read-side critical section, so the writer
  31          * cannot both change sem->state from readers_fast and start checking
  32          * counters while we are here. So if we see !sem->state, we know that
  33          * the writer won't be checking until we're past the preempt_enable()
  34          * and that one the synchronize_sched() is done, the writer will see
  35          * anything we did within this RCU-sched read-size critical section.
  36          */
  37         __this_cpu_inc(*sem->read_count);
  38         if (unlikely(!rcu_sync_is_idle(&sem->rss)))
  39                 __percpu_down_read(sem, false); /* Unconditional memory barrier */
  40         preempt_enable();
  41         /*
  42          * The barrier() from preempt_enable() prevents the compiler from
  43          * bleeding the critical section out.
  44          */
  45 }
  46
  47 static inline int percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
  48 {
  49         int ret = 1;
  50
  51         preempt_disable();
  52         /*
  53          * Same as in percpu_down_read().
  54          */
  55         __this_cpu_inc(*sem->read_count);
  56         if (unlikely(!rcu_sync_is_idle(&sem->rss)))
  57                 ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
  58         preempt_enable();
  59         /*
  60          * The barrier() from preempt_enable() prevents the compiler from
  61          * bleeding the critical section out.
  62          */
  63
  64         if (ret)
  65                 rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 1, _RET_IP_);
  66
  67         return ret;
  68 }
  69
  70 static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
  71 {
  72         /*
  73          * The barrier() in preempt_disable() prevents the compiler from
  74          * bleeding the critical section out.
  75          */
  76         preempt_disable();
  77         /*
  78          * Same as in percpu_down_read().
  79          */
  80         if (likely(rcu_sync_is_idle(&sem->rss)))
  81                 __this_cpu_dec(*sem->read_count);
  82         else
  83                 __percpu_up_read(sem); /* Unconditional memory barrier */
  84         preempt_enable();
  85
  86         rwsem_release(&sem->rw_sem.dep_map, 1, _RET_IP_);
  87 }
  88
  89 extern void percpu_down_write(struct percpu_rw_semaphore *);
  90 extern void percpu_up_write(struct percpu_rw_semaphore *);
  91
  92 extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
  93                                 const char *, struct lock_class_key *);
  94
  95 extern void percpu_free_rwsem(struct percpu_rw_semaphore *);
  96
  97 #define percpu_init_rwsem(sem)                                  \
  98 ({                                                              \
  99         static struct lock_class_key rwsem_key;                 \
 100         __percpu_init_rwsem(sem, #sem, &rwsem_key);             \
 101 })
 102
 103 #define percpu_rwsem_is_held(sem) lockdep_is_held(&(sem)->rw_sem)
 104
 105 static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
 106                                         bool read, unsigned long ip)
 107 {
 108         lock_release(&sem->rw_sem.dep_map, 1, ip);
 109 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 110         if (!read)
 111                 sem->rw_sem.owner = NULL;
 112 #endif
 113 }
 114
 115 static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
 116                                         bool read, unsigned long ip)
 117 {
 118         lock_acquire(&sem->rw_sem.dep_map, 0, 1, read, 1, NULL, ip);
 119 }
 120
 121 #endif