PATCH: prototype "handle broken IRQ routing" patch

[Alan Cox <alan@redhat.com>]

This works a treat on several boxes that otherwise simply won't run Linux
in any useful form. The theory is simple - if an IRQ is delivered to the wrong 
place then someone somewhere in our IRQ handler lists knows what to do with it.

Its if(1) for now, obviously its a boot option and if(my_computer_sucks) in
a final version.


diff -u --new-file --recursive --exclude-from /usr/src/exclude linux-2.6.8.1/arch/i386/kernel/irq.c linux-2.6.8.1.ac/arch/i386/kernel/irq.c
--- linux-2.6.8.1/arch/i386/kernel/irq.c	2004-08-14 11:54:48.000000000 +0100
+++ linux-2.6.8.1.ac/arch/i386/kernel/irq.c	2004-09-03 09:15:17.000000000 +0100
@@ -280,6 +280,38 @@
 __setup("noirqdebug", noirqdebug_setup);
 
 /*
+ *	Recovery handler for misrouted interrupts
+ */
+
+static int misrouted_irq(int irq, irq_desc_t *desc, struct pt_regs *regs)
+{
+	int i;
+	for(i = 1; i < NR_IRQS; i++)
+	{
+		struct irqaction *action;
+		if(i == irq)	/* Already tried */
+			continue;
+		spin_lock(&irq_desc[i].lock);
+		if(irq_desc[i].status & IRQ_INPROGRESS)
+		{
+			spin_unlock(&irq_desc[i].lock);
+			continue;
+		}
+		action = irq_desc[i].action;
+		while(action)
+		{
+			if(action->flags & SA_SHIRQ)
+			{
+				if(action->handler(irq, action->dev_id, regs) == IRQ_HANDLED)
+					desc->irqs_unhandled = 0;
+			}
+			action = action->next;
+		}
+		spin_unlock(&irq_desc[i].lock);
+	}
+}
+
+/*
  * If 99,900 of the previous 100,000 interrupts have not been handled then
  * assume that the IRQ is stuck in some manner.  Drop a diagnostic and try to
  * turn the IRQ off.
@@ -289,13 +321,68 @@
  *
  * Called under desc->lock
  */
-static void note_interrupt(int irq, irq_desc_t *desc, irqreturn_t action_ret)
+static void note_interrupt(int irq, irq_desc_t *desc, irqreturn_t action_ret, struct pt_regs *regs)
 {
 	if (action_ret != IRQ_HANDLED) {
 		desc->irqs_unhandled++;
 		if (action_ret != IRQ_NONE)
 			report_bad_irq(irq, desc, action_ret);
 	}
+	if(1)
+	{
+#ifdef CONFIG_4KSTACKS
+		irqreturn_t action_ret;
+		u32 *isp;
+		union irq_ctx * curctx;
+		union irq_ctx * irqctx;
+
+		curctx = (union irq_ctx *) current_thread_info();
+		irqctx = hardirq_ctx[smp_processor_id()];
+
+		spin_unlock(&desc->lock);
+
+		/*
+		 * this is where we switch to the IRQ stack. However, if we are already using
+		 * the IRQ stack (because we interrupted a hardirq handler) we can't do that
+		 * and just have to keep using the current stack (which is the irq stack already
+		 * after all)
+		 */
+
+		if (curctx == irqctx)
+			misrouted_irq(irq, desc, regs);
+		else {
+			/* build the stack frame on the IRQ stack */
+			isp = (u32*) ((char*)irqctx + sizeof(*irqctx));
+			irqctx->tinfo.task = curctx->tinfo.task;
+			irqctx->tinfo.previous_esp = current_stack_pointer();
+
+			*--isp = (u32) regs;
+			*--isp = (u32) desc;
+			*--isp = (u32) irq;
+
+			asm volatile(
+				"       xchgl   %%ebx,%%esp     \n"
+				"       call    misrouted_irq   \n"
+				"       xchgl   %%ebx,%%esp     \n"
+				: "=a"(action_ret)
+				: "b"(isp)
+				: "memory", "cc", "edx", "ecx"
+			);
+
+
+		}
+		spin_lock(&desc->lock);
+		if (curctx != irqctx)
+			irqctx->tinfo.task = NULL;
+#else
+		irqreturn_t action_ret;
+		spin_unlock(&desc->lock);
+
+		misrouted_irq(irq, desc, regs);
+
+		spin_lock(&desc->lock);
+#endif
+	}
 
 	desc->irq_count++;
 	if (desc->irq_count < 100000)
@@ -487,7 +574,7 @@
 	 * useful for irq hardware that does not mask cleanly in an
 	 * SMP environment.
 	 */
-#ifdef CONFIG_4KSTACKS
+ #ifdef CONFIG_4KSTACKS
 
 	for (;;) {
 		irqreturn_t action_ret;
@@ -532,7 +619,7 @@
 		}
 		spin_lock(&desc->lock);
 		if (!noirqdebug)
-			note_interrupt(irq, desc, action_ret);
+			note_interrupt(irq, desc, action_ret, &regs);
 		if (curctx != irqctx)
 			irqctx->tinfo.task = NULL;
 		if (likely(!(desc->status & IRQ_PENDING)))
@@ -551,7 +638,7 @@
 
 		spin_lock(&desc->lock);
 		if (!noirqdebug)
-			note_interrupt(irq, desc, action_ret);
+			note_interrupt(irq, desc, action_ret, &regs);
 		if (likely(!(desc->status & IRQ_PENDING)))
 			break;
 		desc->status &= ~IRQ_PENDING;