Can the scheduler or some critical kernel threads be preempted in a preemptible Linux kernel? What about in an interrupt handler (top half or bottom half)?
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The scheduler is not a kernel task (but it manages these preemptable tasks) – Basile Starynkevitch Jan 19 '15 at 06:17
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So what is the scheduler? A userspace program if not kernel task? – WindChaser Jan 19 '15 at 16:28
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The scheduler is an essential part of the kernel, but it is not a kernel task – Basile Starynkevitch Jan 19 '15 at 17:49
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Could you tell me the difference? Thanks. – WindChaser Jan 19 '15 at 18:23
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You should take several hours to read some material about operating system & kernel. – Basile Starynkevitch Jan 19 '15 at 18:40
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I cannot find the concept "kernel task" when searching several Linux kernel books (using string matching)... – WindChaser Jan 19 '15 at 19:54
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The kernel calls __schedule() to do the actual context switch. It always call this with preemption disabled. You can search the callers and notice the call to preempt_disable before calling __schedule. So, it can't be preempted.
Also, an interrupt handler cannot be preempted. Preemption is disabled here. But linux kernel is preemptible which means kernel threads and other code can be preempted if it is safe.
bornfree
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Any kernel thread or generally speaking any portion of code can be preempted :
- By a thread of higher priority
- While not in a section protected against interrupts and preemption
So yes even the scheduler can be preempted by a hardware interrupt for instance.
MSI
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