linux-kernel - Re: 2.6.21-rc7-mm2 "irqpoll" seems to be broken

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Date:	Mon, 14 May 2007 16:05:15 +0200
From:	Bernhard Walle <bwalle@...e.de>
To:	Vivek Goyal <vgoyal@...ibm.com>
Cc:	Morton Andrew Morton <akpm@...ux-foundation.org>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.21-rc7-mm2 "irqpoll" seems to be broken

* Vivek Goyal <vgoyal@...ibm.com> [2007-05-08 19:18]:
> On Thu, May 03, 2007 at 12:19:32AM +0200, Bernhard Walle wrote:
> > * Vivek Goyal <vgoyal@...ibm.com> [2007-04-30 10:48]:
> > > 
> > > handle_edge_irq() already makes sure that desc->action is not null, still
> > > note_interrupt() is receiving desc->action as null, that's strange. On my 
> > > system this is happening for irq 4 and /proc/interrupt shows that it is
> > > coming from "serial".
> > 
> > Unfortunately, I couldn't reproduce this here. Vivek, do you have time
> > to take a look at this at your site? For the meanwhile, should I
> > create a patch that checks for desc->action in note_interrupt(), too?
> 
> I can reproduce this problem only on one machine. I think there is some
> race condition and your code somehow just exposes it.

thanks for finding that out. Could you try/review out the patch below?
As the lock is only aquired when irqfixup == 2 it shouldn't impact
performance of a 'normal' system.

Thanks,
   Bernhard

---
 kernel/irq/spurious.c |   18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

--- a/kernel/irq/spurious.c
+++ b/kernel/irq/spurious.c
@@ -145,10 +145,20 @@ void note_interrupt(unsigned int irq, st
 	}
 
 	if (unlikely(irqfixup)) {
-		/* Don't punish working computers */
-		if ((irqfixup == 2 && ((irq == 0) ||
-				(desc->action->flags & IRQF_IRQPOLL))) ||
-				action_ret == IRQ_NONE) {
+		int call_misrouted_irq = action_ret == IRQ_NONE;
+
+		if (!call_misrouted_irq && irqfixup == 2) {
+			if (irq == 0)
+				call_misrouted_irq = 1;
+			else {
+				spin_lock(&desc->lock);
+				if (desc->action && (desc->action->flags & IRQF_IRQPOLL))
+					call_misrouted_irq = 1;
+				spin_unlock(&desc->lock);
+			}
+		}
+
+		if (call_misrouted_irq) {
 			int ok = misrouted_irq(irq);
 			if (action_ret == IRQ_NONE)
 				desc->irqs_unhandled -= ok;
-
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