On Fri, 19 Oct 2007, Benjamin Herrenschmidt wrote:
>
> I agree and you can see that in fact, we don't have enough barrier on
> the other side since spin_unlock doesn't prevent subsequent loads from
> crossing a previous store...
>
> I wonder if that's worth trying to address, adding a barrier in
> handle_IRQ_event for example, or we can continue ignoring the barrier
> and let some drivers do their own fixes in fancy ways.
So how about something like this (untested! not necessarily very well
thought through either!)
Basic notion: the only thing that serializes the IRQ_INPROGRESS flag is
the descriptor lock. And we don't have to (or even want to!) hold it while
waiting for the thing, but we want to *have*held*it* in between whatever
we're synchronizing with.
The internal irq handler functions already held the lock when they did
whatever they need to serialize - and they are possibly performance
critical too - so they use the "internal" function that doesn't get the
lock unnecessarily again.
Hmm?
Linus
---
kernel/irq/manage.c | 22 ++++++++++++++++++----
1 files changed, 18 insertions(+), 4 deletions(-)
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 80eab7a..f3e9575 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -14,6 +14,18 @@
#include "internals.h"
+/*
+ * Internally wait for IRQ_INPROGRESS to go away on other CPU's,
+ * after having serialized with the descriptor lock.
+ */
+static inline void do_synchronize_irq(struct irq_desc *desc)
+{
+#ifdef CONFIG_SMP
+ while (desc->status & IRQ_INPROGRESS)
+ cpu_relax();
+#endif
+}
+
#ifdef CONFIG_SMP
/**
@@ -28,13 +40,15 @@
*/
void synchronize_irq(unsigned int irq)
{
+ unsigned long flags;
struct irq_desc *desc = irq_desc + irq;
if (irq >= NR_IRQS)
return;
- while (desc->status & IRQ_INPROGRESS)
- cpu_relax();
+ spin_lock_irqsave(&desc->lock, flags);
+ spin_unlock_irqrestore(&desc->lock, flags);
+ do_synchronize_irq(desc);
}
EXPORT_SYMBOL(synchronize_irq);
@@ -129,7 +143,7 @@ void disable_irq(unsigned int irq)
disable_irq_nosync(irq);
if (desc->action)
- synchronize_irq(irq);
+ do_synchronize_irq(desc);
}
EXPORT_SYMBOL(disable_irq);
@@ -443,7 +457,7 @@ void free_irq(unsigned int irq, void *dev_id)
unregister_handler_proc(irq, action);
/* Make sure it's not being used on another CPU */
- synchronize_irq(irq);
+ do_synchronize_irq(desc);
#ifdef CONFIG_DEBUG_SHIRQ
/*
* It's a shared IRQ -- the driver ought to be
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