static inline int
execute_on_irq_stack(int overflow, struct irq_desc *desc, int irq)
{
struct irq_stack *curstk, *irqstk;
u32 *isp, *prev_esp, arg1, arg2;
curstk = (struct irq_stack *) current_stack();
irqstk = __this_cpu_read(hardirq_stack);
/*
* this is where we switch to the IRQ stack. However, if we are
* already using the IRQ stack (because we interrupted a hardirq
* handler) we can't do that and just have to keep using the
* current stack (which is the irq stack already after all)
*/
if (unlikely(curstk == irqstk))
return 0;
isp = (u32 *) ((char *)irqstk + sizeof(*irqstk));
/* Save the next esp at the bottom of the stack */
prev_esp = (u32 *)irqstk;
*prev_esp = current_stack_pointer;
if (unlikely(overflow))
call_on_stack(print_stack_overflow, isp);
asm volatile("xchgl %%ebx,%%esp \n"
"call *%%edi \n"
"movl %%ebx,%%esp \n"
: "=a" (arg1), "=d" (arg2), "=b" (isp)
: "0" (irq), "1" (desc), "2" (isp),
"D" (desc->handle_irq)
: "memory", "cc", "ecx");
return 1;
}
The hard IRQ stack is used when handling interrupts. There is one hard IRQ stack for each CPU in the system, and each stack is contained in a single page frame.
The soft IRQ stack is used when handling deferrable functions (softirqs or tasklets; see the later section “Softirqs and Tasklets”). There is one soft IRQ stack for each CPU in the system, and each stack is contained in a single page frame.
1，对于x86硬件而言，在文档325462.pdf卷3章节6.9 PRIORITY AMONG SIMULTANEOUS EXCEPTIONS AND INTERRUPTS 提到一个表格，是指如果在同一时刻有多个异常或中断到达，那么CPU会按照一个指定的优先级顺序对它们进行响应和服务，而并不是我之前所想的判断是否可相互打断执行的高低级别。
2，对于Linux系统而言，硬中断之间并没有优先级的概念（虽然Intel CPU提供支持，请参考文档325462.pdf卷3章节10.8.3 Interrupt, Task, and Processor Priority），或者说优先级只有两个，全部关闭或全部开启，如下：
Regardless of what the hardware might support, typical UNIX-type systems only make use of two levels: the minimum (all interrupts enabled) and the maximum (all interrupts disabled).
When an interrupt is handled through an interrupt gate, the IF flag is automati-
cally cleared, which disables maskable hardware interrupts. (If an interrupt is
handled through a trap gate, the IF flag is not cleared.)
/*
* If the IRQ is disabled for whatever reason, we cannot
* use the action we have.
*/
action = NULL;
if (likely(!(status & (IRQ_DISABLED | IRQ_INPROGRESS)))) {
action = desc->action;
status &= ~IRQ_PENDING; /* we commit to handling */
status |= IRQ_INPROGRESS; /* we are handling it */
}
desc->status = status;
/*
* If there is no IRQ handler or it was disabled, exit early.
* Since we set PENDING, if another processor is handling
* a different instance of this same irq, the other processor
* will take care of it.
*/
if (unlikely(!action))
goto out;
#ifdef CONFIG_LOCKDEP
/* WORKAROUND for lockdep forcing IRQF_DISABLED on us, which
* we don't want and can't tolerate. Although it might be
* friendlier not to borrow this thread context...
*/
local_irq_enable();
#endif
