Just had couple of questions:
1. kernel is preemptible if we are running in kernel mode and not holding any lock. What if we preempt the kernel even when we are holding lock? Assuming process A and B are trying to execute the same kernel path. So what if something like this happens:
A gets into kernel mode and acquires a lock and then B comes, we preempt A and schedule B. B gets into kernel mode, tries to acquire the lock but its not available B goes to sleep, A gets the CPU again goes ahead does its job and releases the lock. B wakes up gets the lock and proceeds normal.
Would there be any problem? I think no. Then why cannot we preempt kernel when we are holding a lock in kernel mode?
2. If kernel is not preemptible then do we really need a separate kernel mode stack for each and every process? I mean cannot we use a common kernel mode stack for all and every process? I think we can because since only one process could be in the kernel mode at a time, any process getting into kernel mode can easily assume that the kernel mode stack is always free whenever it gets into kernel mode.
I know I am wrong somewhere but unable to figure out.
Thanks in advance!
