I am reading Linux Kernel Development recently, and I have a few questions related to disabling preemption.
In the "Interrupt Control" section of chapter 7, it says:
Moreover, disabling interrupts also disables kernel preemption.
I also read from the book that kernel preemption can occur in the follow cases:
When an interrupt handler exits, before returning to kernel-space.
When kernel code becomes preemptible again.
If a task in the kernel explicitly calls schedule()
If a task in ther kernel blocks (which results in a call to schedule())
But I can't relate disabling interrupts with these cases.
As far as I know, a spinlock would disable preemption with the preempt_disable() function.
The post What exactly are "spin-locks"? says:
On a single core machine a spinlock is simply a "disable interrupts" or "raise IRQL" which prevents thread scheduling completely.
Does preempt_disable() disable preemption by disabling interrupts?
I am not a scheduler guru, but I would like to explain how I see it. Here are several things.
thread_info->preempt_count
variable.You can see what is preempt_disable(). Try this: 1. Get a spinlock. 2. Call schedule()
In the dmesg you will see something like "BUG: scheduling while atomic". This happens when scheduler detects that your process in atomic (not preemptive) context but it schedules itself.
Good luck.