关中断或关软中断后，禁抢占是否必要

captivated

回复 39# readerplus


    晕倒...... 这个不是加不加的问题, 是想知道究竟行不行的问题吧...

readerplus

回复 41# captivated
不加当然可以了，前面讨论那么多，不已经共识了嘛。但加上后语意更明确，是一种好的编程习惯
其实内核文档中也有关于是否加不加的说明，可是看了半天也没看出为什么一定要加。

   

readerplus

附上文档说明

Note that you do not need to explicitly prevent preemption if you are holding
any locks or interrupts are disabled, since preemption is implicitly disabled
in those cases.

But keep in mind that 'irqs disabled' is a fundamentally unsafe way of
disabling preemption - any spin_unlock() decreasing the preemption count
to 0 might trigger a reschedule. A simple printk() might trigger a reschedule.
So use this implicit preemption-disabling property only if you know that the
affected codepath does not do any of this. Best policy is to use this only for
small, atomic code that you wrote and which calls no complex functions.

xs3c

spin_irq_lock 没有仔细研究过，我一直以来的理解这个函数就两个功能
＊ 禁止本地中断抢占
＊禁止其他CPU抢占
所以 这里的preempt_disable
当CPU1 上有进程A 进程B B的优先级高于A。 CPU2唤醒CPU1上的进程B。这里至少可以保证CPU1上A进程必须执行完了 才能调用进程B。