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SubjectRe: [RFC][PATCH] IRQ: Fix oneshot irq race between irq_finalize_oneshot and handle_level_irq
On Wed, Mar 10, 2010 at 12:22:12AM +0100, Thomas Gleixner wrote:
> B1;2005;0cOn Tue, 9 Mar 2010, Lars-Peter Clausen wrote:
> >
> > - desc->status |= IRQ_INPROGRESS;
> > + desc->status |= IRQ_INPROGRESS | IRQ_ONESHOT_INPROGRESS;
> > raw_spin_unlock(&desc->lock);
>
> That keeps the IRQ_ONESHOT_INPROGRESS dangling for non ONESHOT
> interrupts. Not a big deal, but not pretty either.
>
> The race between the thread and the irq handler exists indeed on SMP,
> but I think there are more fundamental issues about the state which
> need to be addressed.
>
> The first thing is that we do not mark the status MASKED when we
> actually mask the interrupt in mask_ack_irq().
>
> That conditional MASKED after running the primary handler is really
> horrible - I already ranted in private at the moron who committed that
> crime :)
>
> So the following patch fixes that and the SMP race scenario:

Hi Thomas,

How about the following patch(maybe a little ugly). I think it will
resolve your concerns.

diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index d70394f..23b79c6 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -461,9 +461,24 @@ handle_level_irq(unsigned int irq, struct irq_desc *desc)
raw_spin_lock(&desc->lock);
mask_ack_irq(desc, irq);

- if (unlikely(desc->status & IRQ_INPROGRESS))
- goto out_unlock;
+ /*
+ * if we are in oneshot mode and the irq thread is running on
+ * another cpu, just return because the irq thread will unmask
+ * the irq
+ */
+ if (unlikely(desc->status & IRQ_ONESHOT)) {
+ if (unlikely(desc->status & (IRQ_INPROGRESS | IRQ_MASKED)
+ == IRQ_INPROGRESS | IRQ_MASKED))
+ goto out_unlock;
+ }
+ else {
+ if (unlikely(desc->status & IRQ_INPROGRESS))
+ goto out_unlock;
+ }
+
desc->status &= ~(IRQ_REPLAY | IRQ_WAITING);
+ if (unlikely(desc->status & IRQ_ONESHOT))
+ desc->status |= IRQ_MASKED;
kstat_incr_irqs_this_cpu(irq, desc);

/*
@@ -484,9 +499,7 @@ handle_level_irq(unsigned int irq, struct irq_desc *desc)
raw_spin_lock(&desc->lock);
desc->status &= ~IRQ_INPROGRESS;

- if (unlikely(desc->status & IRQ_ONESHOT))
- desc->status |= IRQ_MASKED;
- else if (!(desc->status & IRQ_DISABLED) && desc->chip->unmask)
+ if (!(desc->status & (IRQ_DISABLED | IRQ_MASKED) && desc->chip->unmask)
desc->chip->unmask(irq);
out_unlock:
raw_spin_unlock(&desc->lock);

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