lib/brlock.c

   1 /*
   2  *
   3  * linux/lib/brlock.c
   4  *
   5  * 'Big Reader' read-write spinlocks.  See linux/brlock.h for details.
   6  *
   7  * Copyright 2000, Ingo Molnar <mingo@redhat.com>
   8  * Copyright 2000, David S. Miller <davem@redhat.com>
   9  */
  10
  11 #include <linux/config.h>
  12
  13 #ifdef CONFIG_SMP
  14
  15 #include <linux/sched.h>
  16 #include <linux/brlock.h>
  17
  18 #ifdef __BRLOCK_USE_ATOMICS
  19
  20 brlock_read_lock_t __brlock_array[NR_CPUS][__BR_IDX_MAX] =
  21    { [0 ... NR_CPUS-1] = { [0 ... __BR_IDX_MAX-1] = RW_LOCK_UNLOCKED } };
  22
  23 void __br_write_lock (enum brlock_indices idx)
  24 {
  25         int i;
  26
  27         preempt_disable();
  28         for (i = 0; i < NR_CPUS; i++)
  29                 _raw_write_lock(&__brlock_array[i][idx]);
  30 }
  31
  32 void __br_write_unlock (enum brlock_indices idx)
  33 {
  34         int i;
  35
  36         for (i = 0; i < NR_CPUS; i++)
  37                 _raw_write_unlock(&__brlock_array[i][idx]);
  38         preempt_enable();
  39 }
  40
  41 #else /* ! __BRLOCK_USE_ATOMICS */
  42
  43 brlock_read_lock_t __brlock_array[NR_CPUS][__BR_IDX_MAX] =
  44    { [0 ... NR_CPUS-1] = { [0 ... __BR_IDX_MAX-1] = 0 } };
  45
  46 struct br_wrlock __br_write_locks[__BR_IDX_MAX] =
  47    { [0 ... __BR_IDX_MAX-1] = { SPIN_LOCK_UNLOCKED } };
  48
  49 void __br_write_lock (enum brlock_indices idx)
  50 {
  51         int i;
  52
  53         preempt_disable();
  54 again:
  55         _raw_spin_lock(&__br_write_locks[idx].lock);
  56         for (i = 0; i < NR_CPUS; i++)
  57                 if (__brlock_array[i][idx] != 0) {
  58                         _raw_spin_unlock(&__br_write_locks[idx].lock);
  59                         barrier();
  60                         cpu_relax();
  61                         goto again;
  62                 }
  63 }
  64
  65 void __br_write_unlock (enum brlock_indices idx)
  66 {
  67         spin_unlock(&__br_write_locks[idx].lock);
  68 }
  69
  70 #endif /* __BRLOCK_USE_ATOMICS */
  71
  72 #endif /* CONFIG_SMP */