Sage-Tips

Can you sleep in interrupt handler?

2 Answers. You can’t sleep in interrupt handlers in Linux because they are not backed by a thread of execution. In other words, they aren’t schedulable entities. Most systems break interrupt processing into two halves, commonly called a top half and a bottom half.

What is interrupt handler in Linux?

An interrupt is simply a signal that the hardware can send when it wants the processor’s attention. Linux handles interrupts in much the same way that it handles signals in user space. For the most part, a driver need only register a handler for its device’s interrupts, and handle them properly when they arrive.

What functions are safe to call from interrupts?

What Functions Are Safe To Call From Interrupts?…In particular, registration and deregistration functions usually expect to be called from user context, and can sleep.

• Accesses to userspace:
• kmalloc(GFP_KERNEL)
• mutex_lock_interruptible() and mutex_lock()

How does the kernel handle an interrupt?

Usually the kernel checks the number of unexpected interrupts received on an IRQ line, so as to disable the line in case a faulty hardware device keeps raising an interrupt over and over.

Can you call a function inside an interrupt?

Yes you may. Yet keep the function in question short, you don’t want to spend too much time in interruption. Another way is to set up a variable state in the interruption, and call the function in question in the normal cycle when the variable is in the desired state. Yes, you can.

Can an ISR call a function?

You can call a function from an isr if it is only the isr that is calling the function. Then it can be considered as part of the isr. If some other part of the program is also calling the function, then it must be a re-entrant function. The isr might interrupt when the program is inside the function.

How do I interrupt in Linux?

When you press CTRL-C the current running command or process get Interrupt/kill (SIGINT) signal. This signal means just terminate the process. Most commands/process will honor the SIGINT signal but some may ignore it. You can press Ctrl-D to close the bash shell or open files when using cat command.

How the Linux kernel handles interrupts?

An interrupt request (IRQ) is requested by the programmable interrupt controller (PIC) with the aim of interrupting the CPU and executing the interrupt service routine (ISR). Nowadays, IRQs are handled by an advanced programmable interrupt controller (APIC), which is part of the CPU. Each core has its own APIC.

Why does the Linux kernel handle certain interrupts in two stages top half and bottom half?

These two needs (work and speed) conflict with each other, leaving the driver writer in a bit of a bind. Linux (along with many other systems) resolves this problem by splitting the interrupt handler into two halves. This setup permits the top half to service a new interrupt while the bottom half is still working.

What’s wrong with interrupting a process in kernel mode?

The problem is when you interrupt a process in kernel mode, not one that is in user mode. If you interrupt a kernel thread and let the handler block, it wouldn’t be the same as a normal thread preemption, because you would be simultaneously preempting two unrelated contexts, the kernel thread, and the ISR.

How to put an interrupt handler to sleep?

You cannot sleep in an interrupt handler because interrupts do not have a backing process context, and thus there is nothing to reschedule back into. In other words, interrupt handlers are not associated with a task, so there is nothing to “put to sleep” and (more importantly) “nothing to wake up”. They must run atomically.

Why does the page fault handler sleep in Linux?

Bottom halves often are, however. The reason the page fault handler can sleep is that it is invoked only by code that is running in process context. Because the kernel’s own memory is not pagable, only user-space memory accesses can result in a page fault.

Why can’t I put the interrupt context to sleep?

The problem is that the interrupt context is not a process, and therefore cannot be put to sleep. When an interrupt occurs, the processor saves the registers onto the stack and jumps to the start of the interrupt service routine.