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SubjectRe: 2.6.21-rc7-mm2 "irqpoll" seems to be broken
On Mon, May 14, 2007 at 04:05:15PM +0200, Bernhard Walle wrote:
> * Vivek Goyal <vgoyal@in.ibm.com> [2007-05-08 19:18]:
> > On Thu, May 03, 2007 at 12:19:32AM +0200, Bernhard Walle wrote:
> > > * Vivek Goyal <vgoyal@in.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.
>

Hi Bernhard,

It does fix up my problem. I have modified your patch a bit. I think
new version is little more clear. What do you think?

Thanks
Vivek




o System crashes if booted with irqpoll command line option.

o Problem happens because Inside note_interrupt() we are accessing
desc->action->flag without taking the desc->lock. While accessing it
somebody goes ahead and unregisters the irq handler hence desc->action
is NULL. By the time note_interrupt() checks it, it crashes.

o In my system it is irq 4 seriving to serial driver.

o Take the desc->lock before accessing desc->action->flag.

Signed-off-by: Bernhard Walle <bwalle@suse.de>
Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
---
linux-2.6.21-git12-root/kernel/irq/spurious.c | 23 ++++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)
diff -puN kernel/irq/spurious.c~fix-irqpoll-crash kernel/irq/spurious.c
--- linux-2.6.21-git12/kernel/irq/spurious.c~fix-irqpoll-crash 2007-05-17 17:36:50.000000000 +0530
+++ linux-2.6.21-git12-root/kernel/irq/spurious.c 2007-05-17 17:53:52.000000000 +0530
@@ -138,6 +138,8 @@ report_bad_irq(unsigned int irq, struct
void note_interrupt(unsigned int irq, struct irq_desc *desc,
irqreturn_t action_ret)
{
+ int call_misrouted_irq = 0;
+
if (unlikely(action_ret != IRQ_HANDLED)) {
desc->irqs_unhandled++;
if (unlikely(action_ret != IRQ_NONE))
@@ -146,9 +148,24 @@ 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) {
+ if (action_ret == IRQ_NONE)
+ /* Nobody handled irq. Possibly a misrouted one. */
+ call_misrouted_irq = 1;
+ else if (irqfixup == 2) {
+ /* irqpoll is enabled. Is this the irq driving
+ * polling.
+ */
+ 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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