IRQ handlers must be written with caution!

2 files changed, 16 insertions, 3 deletions

diff --git a/src/kernel/dev/pciide.c b/src/kernel/dev/pciide.c
index f4474ba..429432f 100644
--- a/src/kernel/dev/pciide.c
+++ b/src/kernel/dev/pciide.c
@@ -165,22 +165,25 @@ static thread_t *wait_irq14 = 0, *wait_irq15 = 0, *wait_pciirq = 0;
 
 void irq14_handler(registers_t *regs) {
 	if (wait_irq14) {
-		resume_thread(wait_irq14, true);
+		thread_t *t = wait_irq14;
 		wait_irq14 = 0;
+		resume_thread(t, true);	// may not return depending on conditions
 	}
 }
 
 void irq15_handler(registers_t *regs) {
 	if (wait_irq15) {
-		resume_thread(wait_irq15, true);
+		thread_t *t = wait_irq15;
 		wait_irq15 = 0;
+		resume_thread(t, true);
 	}
 }
 
 void pciirq_handler(int pci_id) {
 	if (wait_pciirq) {
-		resume_thread(wait_pciirq, true);
+		thread_t *t = wait_pciirq;
 		wait_pciirq = 0;
+		resume_thread(t, true);
 	}
 }
 
diff --git a/src/kernel/include/idt.h b/src/kernel/include/idt.h
index d9dd927..2cccfa5 100644
--- a/src/kernel/include/idt.h
+++ b/src/kernel/include/idt.h
@@ -74,6 +74,16 @@ void idt_init();
 void idt_set_ex_handler(int number, isr_handler_t func);	//Set exception handler
 void idt_set_irq_handler(int number, isr_handler_t func);	//Set IRQ handler
 
+// Warning about IRQ handlers :
+// IRQ handlers must not call yield(), because that may not return ! Therefore they cannot
+// use mutexes, memory allocation and most usefull things. Basically the only thing they
+// can do is wake up another thread, so it is a good idea to have a thread that waits for
+// the IRQ and does something when it happens, and the IRQ handler only wakes up that thread
+// when the IRQ happens.
+// Remark on resume_thread : if the second argument is set to true, yield() is called in the
+// function, so it may never return in some circumstances
+// IRQ handlers are never preemptible
+
 void dbg_dump_registers(registers_t*);
 
 /* vim: set ts=4 sw=4 tw=0 noet :*/