kernel/softirq.c

29070 /*
29071  *      linux/kernel/softirq.c
29072  *
29073  *      Copyright (C) 1992 Linus Torvalds
29074  *
29075  * do_bottom_half() runs at normal kernel priority: all
29076  * interrupts enabled.  do_bottom_half() is atomic with
29077  * respect to itself: a bottom_half handler need not be
29078  * re-entrant.
29079  *
29080  * Fixed a disable_bh()/enable_bh() race (was causing a
29081  * console lockup) due bh_mask_count not atomic
29082  * handling. Copyright (C) 1998 Andrea Arcangeli
29083  */
29084 
29085 #include <linux/mm.h>
29086 #include <linux/kernel_stat.h>
29087 #include <linux/interrupt.h>
29088 #include <linux/smp_lock.h>
29089 
29090 #include <asm/io.h>
29091 
29092 /* intr_count died a painless death... -DaveM */
29093 
29094 atomic_t bh_mask_count[32];
29095 unsigned long bh_active = 0;
29096 unsigned long bh_mask = 0;
29097 void (*bh_base[32])(void);
29098 
29099 /* This needs to make sure that only one bottom half
29100  * handler is ever active at a time. We do this without
29101  * locking by doing an atomic increment on the
29102  * intr_count, and checking (nonatomically) against
29103  * 1. Only if it's 1 do we schedule the bottom half.
29104  *
29105  * Note that the non-atomicity of the test (as opposed to
29106  * the actual update) means that the test may fail, and
29107  * _nobody_ runs the handlers if there is a race that
29108  * makes multiple CPU's get here at the same time. That's
29109  * ok, we'll run them next time around.  */
 Комментарий
29110 static inline void run_bottom_halves(void)
29111 {
29112   unsigned long active;
29113   void (**bh)(void);
29114 
29115   active = get_active_bhs();
29116   clear_active_bhs(active);
29117   bh = bh_base;
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29118   do {
29119     if (active & 1)
29120       (*bh)();
29121     bh++;
29122     active >>= 1;
29123   } while (active);
29124 }
29125 
 Комментарий
29126 asmlinkage void do_bottom_half(void)
29127 {
29128   int cpu = smp_processor_id();
29129 
29130   if (softirq_trylock(cpu)) {
29131     if (hardirq_trylock(cpu)) {
29132       __sti();
29133       run_bottom_halves();
29134       __cli();
29135       hardirq_endlock(cpu);
29136     }
29137     softirq_endlock(cpu);
29138   }
29139 }