On Jul 3, 2012 7:55 PM, "Parmenides" <mobile.parmenides@gmail.com> wrote:
Hi,
It is said that kernel can not be preempted in interrupt context and when it is in a critical section protected by a spin lock.
1. For the spinlock case, it is easy to get if preemption is allowed in critical section, the purpose of protection provided by spinlock can not be achieved readily.
I don't know about Linux kernel. But the very prime purpose of a spin lock is to synchronize in the presence of pre-emption. Are u talking about implementing spin lock in the absence of an atomic hardware instruction?
2. For the interrupt context case, I think when processing interrupt, kernel can be preempted in principle. But, this really increases the interrupt processing time which further cause longer response time and data missing in device. Except that, is there any other reasons?
3. Kernel is responsible for prohibiiting passive process switches, namely preemption, in the above cases. But, It seems that it does not take care of active process swtiches, namely yield. For example, some code in a critical section protected by a spinlock can invoke schedule() to switch process passively. Is this the case?
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