kernel/softirq.c

   1 /*
   2  *      linux/kernel/softirq.c
   3  *
   4  *      Copyright (C) 1992 Linus Torvalds
   5  *
   6  * do_bottom_half() runs at normal kernel priority: all interrupts
   7  * enabled.  do_bottom_half() is atomic with respect to itself: a
   8  * bottom_half handler need not be re-entrant.
   9  */
  10
  11 #include <linux/ptrace.h>
  12 #include <linux/errno.h>
  13 #include <linux/kernel_stat.h>
  14 #include <linux/signal.h>
  15 #include <linux/sched.h>
  16 #include <linux/interrupt.h>
  17 #include <linux/mm.h>
  18 #include <linux/smp.h>
  19 #include <linux/smp_lock.h>
  20
  21 #include <asm/system.h>
  22 #include <asm/io.h>
  23 #include <asm/irq.h>
  24 #include <asm/bitops.h>
  25 #include <asm/atomic.h>
  26
  27 /* intr_count died a painless death... -DaveM */
  28
  29 int bh_mask_count[32];
  30 unsigned long bh_active = 0;
  31 unsigned long bh_mask = 0;
  32 void (*bh_base[32])(void);
  33
  34 /*
  35  * This needs to make sure that only one bottom half handler
  36  * is ever active at a time. We do this without locking by
  37  * doing an atomic increment on the intr_count, and checking
  38  * (nonatomically) against 1. Only if it's 1 do we schedule
  39  * the bottom half.
  40  *
  41  * Note that the non-atomicity of the test (as opposed to the
  42  * actual update) means that the test may fail, and _nobody_
  43  * runs the handlers if there is a race that makes multiple
  44  * CPU's get here at the same time. That's ok, we'll run them
  45  * next time around.
  46  */
  47 static inline void run_bottom_halves(void)
  48 {
  49         unsigned long active;
  50         void (**bh)(void);
  51
  52         active = get_active_bhs();
  53         clear_active_bhs(active);
  54         bh = bh_base;
  55         do {
  56                 if (active & 1)
  57                         (*bh)();
  58                 bh++;
  59                 active >>= 1;
  60         } while (active);
  61 }
  62
  63 asmlinkage void do_bottom_half(void)
  64 {
  65         int cpu = smp_processor_id();
  66
  67         if (softirq_trylock(cpu)) {
  68                 if (hardirq_trylock(cpu)) {
  69                         __sti();
  70                         run_bottom_halves();
  71                         hardirq_endlock(cpu);
  72                 }
  73                 softirq_endlock(cpu);
  74         }
  75 }