Arrange the following levels of interrupt protection within the Linux Kernel,…
2023
Arrange the following levels of interrupt protection within the Linux Kernel, in the order of increasing priority.
(A) user mode programs
(B) bottom half interrupt handlers
(C) kernel system service routines
(D) top half interrupt handlers
Choose the correct answer from the options given below :
- A.
(A), (B), (D), (C)
- B.
(A), (C), (B), (D)
- C.
(A), (C), (D), (B)
- D.
(D), (A), (C), (B)
Attempted by 198 students.
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Correct answer: B
Answer: In increasing priority: user mode programs → kernel system service routines → bottom half interrupt handlers → top half interrupt handlers.
Key idea: priority is determined by the execution context: user-space processes are lowest, process-context kernel work (system calls) is higher, deferred interrupt work (bottom halves) is higher still, and immediate interrupt handling (top halves) has the highest priority.
User mode programs: Run in user-space process context and are the most easily preempted; therefore they have the lowest priority.
Kernel system service routines (system calls): Execute in kernel mode but still in process context, so they run at higher priority than user-space code but lower than interrupt handlers.
Bottom half interrupt handlers (softirqs/tasklets): Deferred interrupt processing that runs after the immediate handler; they preempt normal kernel threads and thus have higher priority than system calls.
Top half interrupt handlers: Immediate interrupt handlers that run at the highest priority to service hardware interrupts as they occur.
Therefore the correct order from lowest to highest priority is: user mode programs, kernel system service routines, bottom half interrupt handlers, top half interrupt handlers.