From 0fc4969b866671dfe39b1a9119d0fdc7ea0f63e5 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 1 Aug 2007 17:13:19 +0200
Subject: [PATCH] genirq: temporary fix for level-triggered IRQ resend
Marcin Slusarz reported a ne2k-pci "hung network interface" regression.
delayed disable relies on the ability to re-trigger the interrupt in the
case that a real interrupt happens after the software disable was set.
In this case we actually disable the interrupt on the hardware level
_after_ it occurred.
On enable_irq, we need to re-trigger the interrupt. On i386 this relies
on a hardware resend mechanism (send_IPI_self()).
Actually we only need the resend for edge type interrupts. Level type
interrupts come back once enable_irq() re-enables the interrupt line.
I assume that the interrupt in question is level triggered because it is
shared and above the legacy irqs 0-15:
17: 12 IO-APIC-fasteoi eth1, eth0
Looking into the IO_APIC code, the resend via send_IPI_self() happens
unconditionally. So the resend is done for level and edge interrupts.
This makes the problem more mysterious.
The code in question lib8390.c does
disable_irq();
fiddle_with_the_network_card_hardware()
enable_irq();
The fiddle_with_the_network_card_hardware() might cause interrupts,
which are cleared in the same code path again,
Marcin found that when he disables the irq line on the hardware level
(removing the delayed disable) the card is kept alive.
So the difference is that we can get a resend on enable_irq, when an
interrupt happens during the time, where we are in the disabled region.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
kernel/irq/resend.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/kernel/irq/resend.c b/kernel/irq/resend.c
index 5bfeaed7e4872..c382727468876 100644
--- a/kernel/irq/resend.c
+++ b/kernel/irq/resend.c
@@ -62,6 +62,15 @@ void check_irq_resend(struct irq_desc *desc, unsigned int irq)
*/
desc->chip->enable(irq);
+ /*
+ * Temporary hack to figure out more about the problem, which
+ * is causing the ancient network cards to die.
+ */
+ if (desc->handle_irq != handle_edge_irq) {
+ WARN_ON_ONCE(1);
+ return;
+ }
+
if ((status & (IRQ_PENDING | IRQ_REPLAY)) == IRQ_PENDING) {
desc->status = (status & ~IRQ_PENDING) | IRQ_REPLAY;
--
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