Re: [PATCH 2.4.19-bk8] arch/i386/kernel/pci-irq.c: Wrong message output

["Mark F. Haigh" <Mark.Haigh@spirentcom.com>]

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Mark F. Haigh wrote:
> 
> Apologies.  Patch now -p1-able.
> 

[Apologies yet again, now includes description]

I'd submitted a patch earlier for this file, fixing a warning.  When I 
looked at it further, I noticed it can output an incorrect warning 
message under certain circumstances.  I've confirmed that this can and 
does happen in the wild:

PCI: Enabling device 0000:00:0a.0 (0000 -> 0001)
PCI: No IRQ known for interrupt pin @ of device 0000:00:0a.0. Probably 
buggy MP table.

It should read "No IRQ known for interrupt pin A", but the 'pin' 
variable has already been decremented (from 1 to 0), so the line:

printk(KERN_WARNING "PCI: No IRQ known for interrupt pin %c of device 
%s.%s\n", 'A' + pin - 1, dev->slot_name, msg);

causes "pin @" to be output, because 'A' + 0 - 1 == '@'.

This patch also fixes the original warning:

pci-irq.c: In function `pcibios_enable_irq':
pci-irq.c:1128: warning: 'msg' might be used uninitialized in this function


Thanks,

Mark Haigh
Mark.Haigh@spirentcom.com

Signed-off-by:  Mark F. Haigh  <Mark.Haigh@spirentcom.com>


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--- linux-2.4.29-bk8/arch/i386/kernel/pci-irq.c.orig	2005-02-07 19:55:23.000000000 -0800
+++ linux-2.4.29-bk8/arch/i386/kernel/pci-irq.c	2005-02-07 20:13:38.000000000 -0800
@@ -1127,6 +1127,8 @@
 	if (pin && !pcibios_lookup_irq(dev, 1) && !dev->irq) {
 		char *msg;
 
+		pin--;		/* interrupt pins are numbered starting from 1 */
+
 		/* With IDE legacy devices the IRQ lookup failure is not a problem.. */
 		if (dev->class >> 8 == PCI_CLASS_STORAGE_IDE && !(dev->class & 0x5))
 			return;
@@ -1134,42 +1136,39 @@
 		if (io_apic_assign_pci_irqs) {
 			int irq;
 
-			if (pin) {
-				pin--;		/* interrupt pins are numbered starting from 1 */
-				irq = IO_APIC_get_PCI_irq_vector(dev->bus->number, PCI_SLOT(dev->devfn), pin);
-				/*
-				 * Busses behind bridges are typically not listed in the MP-table.
-				 * In this case we have to look up the IRQ based on the parent bus,
-				 * parent slot, and pin number. The SMP code detects such bridged
-				 * busses itself so we should get into this branch reliably.
-				 */
-				temp_dev = dev;
-				while (irq < 0 && dev->bus->parent) { /* go back to the bridge */
-					struct pci_dev * bridge = dev->bus->self;
+			irq = IO_APIC_get_PCI_irq_vector(dev->bus->number, PCI_SLOT(dev->devfn), pin);
+			/*
+			 * Busses behind bridges are typically not listed in the MP-table.
+			 * In this case we have to look up the IRQ based on the parent bus,
+			 * parent slot, and pin number. The SMP code detects such bridged
+			 * busses itself so we should get into this branch reliably.
+			 */
+			temp_dev = dev;
+			while (irq < 0 && dev->bus->parent) { /* go back to the bridge */
+				struct pci_dev * bridge = dev->bus->self;
 
-					pin = (pin + PCI_SLOT(dev->devfn)) % 4;
-					irq = IO_APIC_get_PCI_irq_vector(bridge->bus->number, 
-							PCI_SLOT(bridge->devfn), pin);
-					if (irq >= 0)
-						printk(KERN_WARNING "PCI: using PPB(B%d,I%d,P%d) to get irq %d\n", 
-							bridge->bus->number, PCI_SLOT(bridge->devfn), pin, irq);
-					dev = bridge;
-				}
-				dev = temp_dev;
-				if (irq >= 0) {
-					printk(KERN_INFO "PCI->APIC IRQ transform: (B%d,I%d,P%d) -> %d\n",
-						dev->bus->number, PCI_SLOT(dev->devfn), pin, irq);
-					dev->irq = irq;
-					return;
-				} else
-					msg = " Probably buggy MP table.";
+				pin = (pin + PCI_SLOT(dev->devfn)) % 4;
+				irq = IO_APIC_get_PCI_irq_vector(bridge->bus->number, 
+						PCI_SLOT(bridge->devfn), pin);
+				if (irq >= 0)
+					printk(KERN_WARNING "PCI: using PPB(B%d,I%d,P%d) to get irq %d\n", 
+						bridge->bus->number, PCI_SLOT(bridge->devfn), pin, irq);
+				dev = bridge;
 			}
+			dev = temp_dev;
+			if (irq >= 0) {
+				printk(KERN_INFO "PCI->APIC IRQ transform: (B%d,I%d,P%d) -> %d\n",
+					dev->bus->number, PCI_SLOT(dev->devfn), pin, irq);
+				dev->irq = irq;
+				return;
+			} else
+				msg = " Probably buggy MP table.";
 		} else if (pci_probe & PCI_BIOS_IRQ_SCAN)
 			msg = "";
 		else
 			msg = " Please try using pci=biosirq.";
 		printk(KERN_WARNING "PCI: No IRQ known for interrupt pin %c of device %s.%s\n",
-		       'A' + pin - 1, dev->slot_name, msg);
+		       'A' + pin, dev->slot_name, msg);
 	}
 	/* VIA bridges use interrupt line for apic/pci steering across
 	   the V-Link */