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  * Fixed a disable_bh()/enable_bh() race (was causing a console lockup)
  11  * due bh_mask_count not atomic handling. Copyright (C) 1998  Andrea Arcangeli
  12  */
  13
  14 #include <linux/mm.h>
  15 #include <linux/kernel_stat.h>
  16 #include <linux/interrupt.h>
  17 #include <linux/smp_lock.h>
  18
  19 #include <asm/io.h>
  20
  21 /* intr_count died a painless death... -DaveM */
  22
  23 atomic_t bh_mask_count[32];
  24 unsigned long bh_active = 0;
  25 unsigned long bh_mask = 0;
  26 void (*bh_base[32])(void);
  27
  28 /*
  29  * This needs to make sure that only one bottom half handler
  30  * is ever active at a time. We do this without locking by
  31  * doing an atomic increment on the intr_count, and checking
  32  * (nonatomically) against 1. Only if it's 1 do we schedule
  33  * the bottom half.
  34  *
  35  * Note that the non-atomicity of the test (as opposed to the
  36  * actual update) means that the test may fail, and _nobody_
  37  * runs the handlers if there is a race that makes multiple
  38  * CPU's get here at the same time. That's ok, we'll run them
  39  * next time around.
  40  */
  41 static inline void run_bottom_halves(void)
  42 {
  43         unsigned long active;
  44         void (**bh)(void);
  45
  46         active = get_active_bhs();
  47         clear_active_bhs(active);
  48         bh = bh_base;
  49         do {
  50                 if (active & 1)
  51                         (*bh)();
  52                 bh++;
  53                 active >>= 1;
  54         } while (active);
  55 }
  56
  57 asmlinkage void do_bottom_half(void)
  58 {
  59         int cpu = smp_processor_id();
  60
  61         if (softirq_trylock(cpu)) {
  62                 if (hardirq_trylock(cpu)) {
  63                         __sti();
  64                         run_bottom_halves();
  65                         __cli();
  66                         hardirq_endlock(cpu);
  67                 }
  68                 softirq_endlock(cpu);
  69         }
  70 }