PCI Hotplug: acpiphp: don't store a pci_dev in acpiphp_func

An oops can occur if a user attempts to use both PCI logical
hotplug and the ACPI physical hotplug driver (acpiphp) in this
sequence, where $slot/address == $device.

In other words, if acpiphp has claimed a PCI device, and that
device is logically removed, then acpiphp may oops when it
attempts to access it again.

	# echo 1 > /sys/bus/pci/devices/$device/remove
	# echo 0 > /sys/bus/pci/slots/$slot/power

Unable to handle kernel NULL pointer dereference (address 0000000000000000)
Call Trace:
 [<a000000100016390>] show_stack+0x50/0xa0
 [<a000000100016c60>] show_regs+0x820/0x860
 [<a00000010003b390>] die+0x190/0x2a0
 [<a000000100066a40>] ia64_do_page_fault+0x8e0/0xa40
 [<a00000010000c7a0>] ia64_native_leave_kernel+0x0/0x270
 [<a0000001003b2660>] pci_remove_bus_device+0x120/0x260
 [<a0000002060549f0>] acpiphp_disable_slot+0x410/0x540 [acpiphp]
 [<a0000002060505c0>] disable_slot+0xc0/0x120 [acpiphp]
 [<a0000002040d21c0>] power_write_file+0x1e0/0x2a0 [pci_hotplug]
 [<a0000001003bb820>] pci_slot_attr_store+0x60/0xa0
 [<a000000100240f70>] sysfs_write_file+0x230/0x2c0
 [<a000000100195750>] vfs_write+0x190/0x2e0
 [<a0000001001961a0>] sys_write+0x80/0x100
 [<a00000010000c600>] ia64_ret_from_syscall+0x0/0x20
 [<a000000000010720>] __kernel_syscall_via_break+0x0/0x20

The root cause of this oops is that the logical remove ("echo 1 >
/sys/bus/pci/devices/$device/remove") destroyed the pci_dev. The
pci_dev struct itself wasn't deallocated because acpiphp kept a
reference, but some of its fields became invalid.

acpiphp doesn't have any real reason to keep a pointer to a
pci_dev around. It can always derive it using pci_get_slot().

If a logical remove destroys the pci_dev, acpiphp won't find it
and is thus prevented from causing mischief.

Reviewed-by: Matthew Wilcox <willy@linux.intel.com>
Reviewed-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Tested-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Reported-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Acked-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

drivers/pci/hotplug/acpiphp.h

@@ -129,7 +129,6 @@ struct acpiphp_func {
 	struct acpiphp_bridge *bridge;	/* Ejectable PCI-to-PCI bridge */
 
 	struct list_head sibling;
-	struct pci_dev *pci_dev;
 	struct notifier_block nb;
 	acpi_handle	handle;
 

drivers/pci/hotplug/acpiphp_glue.c

@@ -32,9 +32,6 @@
 
 /*
  * Lifetime rules for pci_dev:
- *  - The one in acpiphp_func has its refcount elevated by pci_get_slot()
- *    when the driver is loaded or when an insertion event occurs.  It loses
- *    a refcount when its ejected or the driver unloads.
  *  - The one in acpiphp_bridge has its refcount elevated by pci_get_slot()
  *    when the bridge is scanned and it loses a refcount when the bridge
  *    is removed.
@@ -130,6 +127,7 @@ register_slot(acpi_handle handle, u32 lvl, void *context, void **rv)
 	unsigned long long adr, sun;
 	int device, function, retval;
 	struct pci_bus *pbus = bridge->pci_bus;
+	struct pci_dev *pdev;
 
 	if (!acpi_pci_check_ejectable(pbus, handle) && !is_dock_device(handle))
 		return AE_OK;
@@ -213,10 +211,10 @@ register_slot(acpi_handle handle, u32 lvl, void *context, void **rv)
 	newfunc->slot = slot;
 	list_add_tail(&newfunc->sibling, &slot->funcs);
 
-	/* associate corresponding pci_dev */
-	newfunc->pci_dev = pci_get_slot(pbus, PCI_DEVFN(device, function));
-	if (newfunc->pci_dev) {
+	pdev = pci_get_slot(pbus, PCI_DEVFN(device, function));
+	if (pdev) {
 		slot->flags |= (SLOT_ENABLED | SLOT_POWEREDON);
+		pci_dev_put(pdev);
 	}
 
 	if (is_dock_device(handle)) {
@@ -617,7 +615,6 @@ static void cleanup_bridge(struct acpiphp_bridge *bridge)
 				if (ACPI_FAILURE(status))
 					err("failed to remove notify handler\n");
 			}
-			pci_dev_put(func->pci_dev);
 			list_del(list);
 			kfree(func);
 		}
@@ -1101,22 +1098,24 @@ static int __ref enable_device(struct acpiphp_slot *slot)
 	pci_enable_bridges(bus);
 	pci_bus_add_devices(bus);
 
-	/* associate pci_dev to our representation */
 	list_for_each (l, &slot->funcs) {
 		func = list_entry(l, struct acpiphp_func, sibling);
-		func->pci_dev = pci_get_slot(bus, PCI_DEVFN(slot->device,
-							func->function));
-		if (!func->pci_dev)
+		dev = pci_get_slot(bus, PCI_DEVFN(slot->device,
+						  func->function));
+		if (!dev)
 			continue;
 
-		if (func->pci_dev->hdr_type != PCI_HEADER_TYPE_BRIDGE &&
-		    func->pci_dev->hdr_type != PCI_HEADER_TYPE_CARDBUS)
+		if (dev->hdr_type != PCI_HEADER_TYPE_BRIDGE &&
+		    dev->hdr_type != PCI_HEADER_TYPE_CARDBUS) {
+			pci_dev_put(dev);
 			continue;
+		}
 
 		status = find_p2p_bridge(func->handle, (u32)1, bus, NULL);
 		if (ACPI_FAILURE(status))
 			warn("find_p2p_bridge failed (error code = 0x%x)\n",
 				status);
+		pci_dev_put(dev);
 	}
 
 	slot->flags |= SLOT_ENABLED;
@@ -1142,17 +1141,14 @@ static void disable_bridges(struct pci_bus *bus)
  */
 static int disable_device(struct acpiphp_slot *slot)
 {
-	int retval = 0;
 	struct acpiphp_func *func;
-	struct list_head *l;
+	struct pci_dev *pdev;
 
 	/* is this slot already disabled? */
 	if (!(slot->flags & SLOT_ENABLED))
 		goto err_exit;
 
-	list_for_each (l, &slot->funcs) {
-		func = list_entry(l, struct acpiphp_func, sibling);
-
+	list_for_each_entry(func, &slot->funcs, sibling) {
 		if (func->bridge) {
 			/* cleanup p2p bridges under this P2P bridge */
 			cleanup_p2p_bridge(func->bridge->handle,
@@ -1160,35 +1156,28 @@ static int disable_device(struct acpiphp_slot *slot)
 			func->bridge = NULL;
 		}
 
-		if (func->pci_dev) {
-			pci_stop_bus_device(func->pci_dev);
-			if (func->pci_dev->subordinate) {
-				disable_bridges(func->pci_dev->subordinate);
-				pci_disable_device(func->pci_dev);
+		pdev = pci_get_slot(slot->bridge->pci_bus,
+				    PCI_DEVFN(slot->device, func->function));
+		if (pdev) {
+			pci_stop_bus_device(pdev);
+			if (pdev->subordinate) {
+				disable_bridges(pdev->subordinate);
+				pci_disable_device(pdev);
 			}
+			pci_remove_bus_device(pdev);
+			pci_dev_put(pdev);
 		}
 	}
 
-	list_for_each (l, &slot->funcs) {
-		func = list_entry(l, struct acpiphp_func, sibling);
-
+	list_for_each_entry(func, &slot->funcs, sibling) {
 		acpiphp_unconfigure_ioapics(func->handle);
 		acpiphp_bus_trim(func->handle);
-		/* try to remove anyway.
-		 * acpiphp_bus_add might have been failed */
-
-		if (!func->pci_dev)
-			continue;
-
-		pci_remove_bus_device(func->pci_dev);
-		pci_dev_put(func->pci_dev);
-		func->pci_dev = NULL;
 	}
 
 	slot->flags &= (~SLOT_ENABLED);
 
- err_exit:
-	return retval;
+err_exit:
+	return 0;
 }