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 #include <linux/delay.h>
  18
  19 #ifdef __BRLOCK_USE_ATOMICS
  20
  21 brlock_read_lock_t __brlock_array[NR_CPUS][__BR_IDX_MAX] =
  22    { [0 ... NR_CPUS-1] = { [0 ... __BR_IDX_MAX-1] = RW_LOCK_UNLOCKED } };
  23
  24 void __br_write_lock (enum brlock_indices idx)
  25 {
  26         int i;
  27
  28         for (i = 0; i < smp_num_cpus; i++)
  29                 write_lock(&__brlock_array[cpu_logical_map(i)][idx]);
  30 }
  31
  32 void __br_write_unlock (enum brlock_indices idx)
  33 {
  34         int i;
  35
  36         for (i = 0; i < smp_num_cpus; i++)
  37                 write_unlock(&__brlock_array[cpu_logical_map(i)][idx]);
  38 }
  39
  40 #else /* ! __BRLOCK_USE_ATOMICS */
  41
  42 brlock_read_lock_t __brlock_array[NR_CPUS][__BR_IDX_MAX] =
  43    { [0 ... NR_CPUS-1] = { [0 ... __BR_IDX_MAX-1] = 0 } };
  44
  45 struct br_wrlock __br_write_locks[__BR_IDX_MAX] =
  46    { [0 ... __BR_IDX_MAX-1] = { SPIN_LOCK_UNLOCKED } };
  47
  48 void __br_write_lock (enum brlock_indices idx)
  49 {
  50         int i;
  51
  52 again:
  53         spin_lock(&__br_write_locks[idx].lock);
  54         for (i = 0; i < smp_num_cpus; i++)
  55                 if (__brlock_array[cpu_logical_map(i)][idx] != 0) {
  56                         spin_unlock(&__br_write_locks[idx].lock);
  57                         barrier();
  58                         cpu_relax();
  59                         goto again;
  60                 }
  61 }
  62
  63 void __br_write_unlock (enum brlock_indices idx)
  64 {
  65         spin_unlock(&__br_write_locks[idx].lock);
  66 }
  67
  68 #endif /* __BRLOCK_USE_ATOMICS */
  69
  70 #endif /* CONFIG_SMP */