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标题: 单核arm中spin_lock没有被实现，请问这时用什么机制在中断中做同步？ [打印本页]

作者: tassard 时间: 2010-07-06 16:45
标题: 单核arm中spin_lock没有被实现，请问这时用什么机制在中断中做同步？
下面代码的运行平台是单核arm，使用spin_lock保证对reg_atomic_1和reg_atomic_2的原子访问，但是查阅一些资料后发现在单核arm平台上spin_lock没有实现！！那请问下面的代码要怎么在中断中做同步？谢谢。

附代码：

int reg_atomic_1 = 0;
int reg_atomic_2 = 0;

void test()
{
unsigned long iflags;
spin_lock_irqsave(lock, iflags);

reg_atomic_1 = 1;
reg_atomic_2 = 1;

spin_unlock_irqrestore(lock, iflags);
}

static irqreturn_t irq_func(int irq, void *dev_id)
{
unsigned long iflags;
spin_lock_irqsave(lock, iflags);

reg_atomic_1 = 2;
reg_atomic_2 = 2;

spin_unlock_irqrestore(lock, iflags);
}

作者: kgn28 时间: 2010-07-06 17:00
回复 1# tassard

不需要修改吧，见这个帖子的讨论：http://linux.chinaunix.net/bbs/thread-1166513-1-1.html

作者: snail_314 时间: 2010-07-06 17:04
回复 1# tassard

spin_lock不管在什么平台上都没有实现,因为,没有这个需求(既然都单核了,就不会出现非中断的执行序并行执行了).
但是,spin_lock未实现并不意味着spin_lock_irqsave是个空操作,它至少还有关中断\保护现场的操作,而spin_lock_irqrestore也有恢复现场\开中断的操作.所以,执行序和中断历程之间还是有保护的,赫赫

作者: jinxinxin163 时间: 2010-07-06 21:52
在up下，spin_lock_irqsave的功能退化为“关闭本地cpu的中断”，下面这个网址对你的问题应该有所帮助
http://blog.chinaunix.net/u2/73067/showart_2046163.html

作者: tassard 时间: 2010-07-07 15:58
谢谢各位，关于spin_lock_irq我明白了，但是还有个问题。
我查了下源代码，发现spin_lock_irq是会关闭中断的，但是spin_lock函数就不会，那既然这样的话，为什么kernel的handle_edge_irq会使用spin_lock函数而不是spin_lock_irq？这样会不会破坏共享数据？谢谢。

void
handle_edge_irq(unsigned int irq, struct irq_desc *desc)
{
spin_lock(&desc->lock);

desc->status &= ~(IRQ_REPLAY | IRQ_WAITING);

/*
   * If we're currently running this IRQ, or its disabled,
   * we shouldn't process the IRQ. Mark it pending, handle
   * the necessary masking and go out
   */
if (unlikely((desc->status & (IRQ_INPROGRESS | IRQ_DISABLED)) ||
      !desc->action)) {
desc->status |= (IRQ_PENDING | IRQ_MASKED);
mask_ack_irq(desc, irq);
goto out_unlock;
}
kstat_incr_irqs_this_cpu(irq, desc);

/* Start handling the irq */
if (desc->chip->ack)
desc->chip->ack(irq);

/* Mark the IRQ currently in progress.*/
desc->status |= IRQ_INPROGRESS;

do {
struct irqaction *action = desc->action;
irqreturn_t action_ret;

if (unlikely(!action)) {
desc->chip->mask(irq);
goto out_unlock;
}

/*
   * When another irq arrived while we were handling
   * one, we could have masked the irq.
   * Renable it, if it was not disabled in meantime.
   */
if (unlikely((desc->status &
         (IRQ_PENDING | IRQ_MASKED | IRQ_DISABLED)) ==
      (IRQ_PENDING | IRQ_MASKED))) {
desc->chip->unmask(irq);
desc->status &= ~IRQ_MASKED;
}

desc->status &= ~IRQ_PENDING;
spin_unlock(&desc->lock);
action_ret = handle_IRQ_event(irq, action);
if (!noirqdebug)
note_interrupt(irq, desc, action_ret);
spin_lock(&desc->lock);

} while ((desc->status & (IRQ_PENDING | IRQ_DISABLED)) == IRQ_PENDING);

desc->status &= ~IRQ_INPROGRESS;
out_unlock:
spin_unlock(&desc->lock);
}

作者: nettom 时间: 2010-07-08 04:23
spin_lock 和spin_unlock使用的前提是中断处理程序和锁之间没有交互

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