Disable interrupts while modifying the IRQ handler list

By disabling interrupts while we lock the IRQs list, we can be
confident that the list is always unlocked when we handle
interrupts, allowing us to lock the list, rather than trying to
lock it and having a fallback option if that fails. This means
we should avoid ignoring interrupts because of a failed attempt
to lock the list.

Author: SlyMarbo

kernel/src/interrupts.rs

@@ -31,6 +31,7 @@
 use crate::{gdt, halt_loop, println, time};
 use lazy_static::lazy_static;
 use pic8259::ChainedPics;
+use x86_64::instructions::interrupts;
 use x86_64::registers::control::Cr2;
 use x86_64::structures::idt::{InterruptDescriptorTable, InterruptStackFrame, PageFaultErrorCode};
 
@@ -130,11 +131,8 @@ fn irq_handler_none(_frame: InterruptStackFrame, _irq: u8) {}
 
 #[inline]
 fn irq_handler_generic(frame: InterruptStackFrame, irq: u8) {
-    let irqs = IRQS.try_lock();
-    if let Some(irqs) = irqs {
-        let handler = irqs[irq as usize];
-        handler(frame, irq);
-    }
+    let handler = IRQS.lock()[irq as usize];
+    handler(frame, irq);
 
     unsafe {
         PICS.lock()
@@ -218,16 +216,18 @@ static IRQS: spin::Mutex<[IrqHandler; 16]> = spin::Mutex::new([irq_handler_none;
 /// panics.
 ///
 pub fn register_irq(irq: u8, handler: IrqHandler) {
-    let mut irqs = IRQS.lock();
     if irq > 15 {
         panic!("invalid IRQ {} passed to register_irq", irq);
     }
 
-    if irqs[irq as usize] != irq_handler_none {
-        panic!("IRQ {} has already been registered", irq);
-    }
+    interrupts::without_interrupts(|| {
+        let mut irqs = IRQS.lock();
+        if irqs[irq as usize] != irq_handler_none {
+            panic!("IRQ {} has already been registered", irq);
+        }
 
-    irqs[irq as usize] = handler;
+        irqs[irq as usize] = handler;
+    });
 }
 
 // Tests