Re: 2.6.13-rc6-rt9

[Thomas Gleixner <tglx@linutronix.de>]

On Thu, 2005-08-18 at 08:01 +0200, Ingo Molnar wrote:
> i have released the 2.6.13-rc6-rt9 tree, which can be downloaded from 
> the usual place:

Hi Ingo,

finally found the deadlock. It was caused by IRQ flood, which was
introduced by the end_irq() changes.

They change the semantics in two ways - both wrong. 

1. The condition is different
2. ->end() can contain different code than ->enable()

That's the code in end_8259A_irq():

	if (!(irq_desc[irq].status & (IRQ_DISABLED|IRQ_INPROGRESS)) &&
							irq_desc[irq].action)
		enable_8259A_irq(irq);

The code in end_irq():

	if (!(desc->status & IRQ_DISABLED))
		desc->handler->enable(irq);


What was the reason for those changes ?

tglx


diff -uprN --exclude-from=/usr/local/bin/diffit.exclude
linux-2.6.13-rc6-rt8/kernel/irq/handle.c
linux-2.6.13-rc6-rt-debug/kernel/irq/handle.c
--- linux-2.6.13-rc6-rt8/kernel/irq/handle.c 2005-08-17
17:53:13.000000000 +0200
+++ linux-2.6.13-rc6-rt-debug/kernel/irq/handle.c 2005-08-18
16:32:54.000000000 +0200
@@ -171,7 +171,7 @@ fastcall notrace unsigned int __do_IRQ(u
*/
desc->handler->ack(irq);
action_ret = handle_IRQ_event(irq, regs, desc->action);
- end_irq(desc, irq);
+ desc->handler->end(irq);
return 1;
}

@@ -241,7 +241,7 @@ out:
* The end-handler has to deal with interrupts which got
* disabled while the handler was running:
*/
- end_irq(desc, irq);
+ desc->handler->end(irq);
out_no_end:
spin_unlock(&desc->lock);
diff -uprN --exclude-from=/usr/local/bin/diffit.exclude linux-2.6.13-rc6-rt8/kernel/irq/internals.h linux-2.6.13-rc6-rt-debug/kernel/irq/internals.h
--- linux-2.6.13-rc6-rt8/kernel/irq/internals.h	2005-08-17 17:53:13.000000000 +0200
+++ linux-2.6.13-rc6-rt-debug/kernel/irq/internals.h	2005-08-18 16:39:56.000000000 +0200
@@ -6,21 +6,6 @@ extern int noirqdebug;
 
 void recalculate_desc_flags(struct irq_desc *desc);
 
-/*
- * On PREEMPT_HARDIRQS, the ->ack handler masks interrupts, so that
- * they can be redirected to an IRQ thread, if needed. So here we
- * have to unmask the interrupt line, if needed:
- */
-static inline void end_irq(irq_desc_t *desc, unsigned int irq)
-{
-#ifdef CONFIG_PREEMPT_HARDIRQS
-	if (!(desc->status & IRQ_DISABLED))
-		desc->handler->enable(irq);
-#else
-	desc->handler->end(irq);
-#endif
-}
-
 #ifdef CONFIG_PROC_FS
 extern void register_irq_proc(unsigned int irq);
 extern void register_handler_proc(unsigned int irq, struct irqaction *action);
diff -uprN --exclude-from=/usr/local/bin/diffit.exclude linux-2.6.13-rc6-rt8/kernel/irq/manage.c linux-2.6.13-rc6-rt-debug/kernel/irq/manage.c
--- linux-2.6.13-rc6-rt8/kernel/irq/manage.c	2005-08-17 17:53:13.000000000 +0200
+++ linux-2.6.13-rc6-rt-debug/kernel/irq/manage.c	2005-08-18 16:31:46.000000000 +0200
@@ -442,7 +442,7 @@ static void do_hardirq(struct irq_desc *
 		 * The end-handler has to deal with interrupts which got
 		 * disabled while the handler was running:
 		 */
-		end_irq(desc, irq);
+		desc->handler->end(irq);
 	}
 	spin_unlock_irq(&desc->lock);