[PATCH] 3c503: Fix IRQ probing

[Ben Hutchings <ben@decadent.org.uk>]

The driver attempts to select an IRQ for the NIC automatically by
testing which of the supported IRQs are available and then probing
each available IRQ with probe_irq_{on,off}().  There are obvious race
conditions here, besides which:
1. The test for availability is done by passing a NULL handler, which
   now always returns -EINVAL, thus the device cannot be opened:
   <http://bugs.debian.org/566522>
2. probe_irq_off() will report only the first ISA IRQ handled,
   potentially leading to a false negative.

There was another bug that meant it ignored all error codes from
request_irq() except -EBUSY, so it would 'succeed' despite this
(possibly causing conflicts with other ISA devices).  This was fixed
by ab08999d6029bb2c79c16be5405d63d2bedbdfea 'WARNING: some
request_irq() failures ignored in el2_open()', which exposed bug 1.

This patch:
1. Replaces the use of probe_irq_{on,off}() with a real interrupt handler
2. Adds a delay before checking the interrupt-seen flag
3. Disables interrupts on all failure paths
4. Distinguishes error codes from the second request_irq() call,
   consistently with the first

Compile-tested only.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 drivers/net/3c503.c |   42 ++++++++++++++++++++++++++++++------------
 1 files changed, 30 insertions(+), 12 deletions(-)

diff --git a/drivers/net/3c503.c b/drivers/net/3c503.c
index 66e0323..b74a0ea 100644
--- a/drivers/net/3c503.c
+++ b/drivers/net/3c503.c
@@ -380,6 +380,12 @@ out:
     return retval;
 }
 
+static irqreturn_t el2_probe_interrupt(int irq, void *seen)
+{
+	*(bool *)seen = true;
+	return IRQ_HANDLED;
+}
+
 static int
 el2_open(struct net_device *dev)
 {
@@ -391,23 +397,35 @@ el2_open(struct net_device *dev)
 
 	outb(EGACFR_NORM, E33G_GACFR);	/* Enable RAM and interrupts. */
 	do {
-	    retval = request_irq(*irqp, NULL, 0, "bogus", dev);
-	    if (retval >= 0) {
+		bool seen;
+
+		retval = request_irq(*irqp, el2_probe_interrupt, 0,
+				     dev->name, &seen);
+		if (retval == -EBUSY)
+			continue;
+		if (retval < 0)
+			goto err_disable;
+
 		/* Twinkle the interrupt, and check if it's seen. */
-		unsigned long cookie = probe_irq_on();
+		seen = false;
+		smp_wmb();
 		outb_p(0x04 << ((*irqp == 9) ? 2 : *irqp), E33G_IDCFR);
 		outb_p(0x00, E33G_IDCFR);
-		if (*irqp == probe_irq_off(cookie) &&	/* It's a good IRQ line! */
-		    ((retval = request_irq(dev->irq = *irqp,
-					   eip_interrupt, 0,
-					   dev->name, dev)) == 0))
-		    break;
-	    } else {
-		    if (retval != -EBUSY)
-			    return retval;
-	    }
+		msleep(1);
+		free_irq(*irqp, el2_probe_interrupt);
+		if (!seen)
+			continue;
+
+		retval = request_irq(dev->irq = *irqp, eip_interrupt, 0,
+				     dev->name, dev);
+		if (retval == -EBUSY)
+			continue;
+		if (retval < 0)
+			goto err_disable;
 	} while (*++irqp);
+
 	if (*irqp == 0) {
+	err_disable:
 	    outb(EGACFR_IRQOFF, E33G_GACFR);	/* disable interrupts. */
 	    return -EAGAIN;
 	}
-- 
1.7.0.3