PCI: prevent duplicate slot names

Prevent callers of pci_create_slot() from registering slots with
duplicate names. This condition occurs most often when PCI hotplug
drivers are loaded on platforms with broken firmware that assigns
identical names to multiple slots.

We now rename these duplicate slots on behalf of the user.

If firmware assigns the name N to multiple slots, then:

	The first registered slot is assigned N
	The second registered slot is assigned N-1
	The third registered slot is assigned N-2
	etc.

This is the permanent fix mentioned in earlier commits d6a9e9b4 and
167e782e (shpchp/pciehp: Rename duplicate slot name...).

We take advantage of the new 'hotplug' parameter in pci_create_slot()
to prevent a slot create/rename race between hotplug drivers and
detection drivers.

	Scenario A:
	hotplug driver                  detection driver
	--------------                  ----------------
	pci_create_slot(hotplug=set)
					pci_create_slot(hotplug=NULL)

The hotplug driver creates the slot with its desired name, and then
releases the semaphore. Now, the detection driver tries to create
the same slot, but it already exists. We don't care about renaming,
so return the existing slot.

	Scenario B:
	hotplug driver                  detection driver
	--------------                  ----------------
					pci_create_slot(hotplug=NULL)
	pci_create_slot(hotplug=set)

The detection driver creates the slot with name "X". Then the hotplug
driver tries to create the same slot, but wants the name "Y" instead.
We detect that we're trying to create the same slot and that we also
want a rename, so rename the slot to "Y" and return.

	Scenario C:
	hotplug driver                  hotplug driver
	--------------                  ----------------
	pci_create_slot(hotplug=set)
					pci_create_slot(hotplug=set)

Two separate hotplug drivers are attempting to claim the slot and
are passing valid hotplug_slot args to pci_create_slot(). We detect
that the slot already has a ->hotplug callback, prevent a rename,
and return -EBUSY.

Cc: kristen.c.accardi@intel.com
Cc: matthew@wil.cx
Acked-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

1 files changed, 113 insertions, 28 deletions

diff --git a/drivers/pci/slot.c b/drivers/pci/slot.c
index 0e009c3ba5f..b6ee352ae45 100644
--- a/drivers/pci/slot.c
+++ b/drivers/pci/slot.c
@@ -78,6 +78,77 @@ static struct kobj_type pci_slot_ktype = {
 	.default_attrs = pci_slot_default_attrs,
 };
 
+static char *make_slot_name(const char *name)
+{
+	char *new_name;
+	int len, max, dup;
+
+	new_name = kstrdup(name, GFP_KERNEL);
+	if (!new_name)
+		return NULL;
+
+	/*
+	 * Make sure we hit the realloc case the first time through the
+	 * loop.  'len' will be strlen(name) + 3 at that point which is
+	 * enough space for "name-X" and the trailing NUL.
+	 */
+	len = strlen(name) + 2;
+	max = 1;
+	dup = 1;
+
+	for (;;) {
+		struct kobject *dup_slot;
+		dup_slot = kset_find_obj(pci_slots_kset, new_name);
+		if (!dup_slot)
+			break;
+		kobject_put(dup_slot);
+		if (dup == max) {
+			len++;
+			max *= 10;
+			kfree(new_name);
+			new_name = kmalloc(len, GFP_KERNEL);
+			if (!new_name)
+				break;
+		}
+		sprintf(new_name, "%s-%d", name, dup++);
+	}
+
+	return new_name;
+}
+
+static int rename_slot(struct pci_slot *slot, const char *name)
+{
+	int result = 0;
+	char *slot_name;
+
+	if (strcmp(kobject_name(&slot->kobj), name) == 0)
+		return result;
+
+	slot_name = make_slot_name(name);
+	if (!slot_name)
+		return -ENOMEM;
+
+	result = kobject_rename(&slot->kobj, slot_name);
+	kfree(slot_name);
+
+	return result;
+}
+
+static struct pci_slot *get_slot(struct pci_bus *parent, int slot_nr)
+{
+	struct pci_slot *slot;
+	/*
+	 * We already hold pci_bus_sem so don't worry
+	 */
+	list_for_each_entry(slot, &parent->slots, list)
+		if (slot->number == slot_nr) {
+			kobject_get(&slot->kobj);
+			return slot;
+		}
+
+	return NULL;
+}
+
 /**
  * pci_create_slot - create or increment refcount for physical PCI slot
  * @parent: struct pci_bus of parent bridge
@@ -90,7 +161,17 @@ static struct kobj_type pci_slot_ktype = {
  * either return a new &struct pci_slot to the caller, or if the pci_slot
  * already exists, its refcount will be incremented.
  *
- * Slots are uniquely identified by a @pci_bus, @slot_nr, @name tuple.
+ * Slots are uniquely identified by a @pci_bus, @slot_nr tuple.
+ *
+ * There are known platforms with broken firmware that assign the same
+ * name to multiple slots. Workaround these broken platforms by renaming
+ * the slots on behalf of the caller. If firmware assigns name N to
+ * multiple slots:
+ *
+ * The first slot is assigned N
+ * The second slot is assigned N-1
+ * The third slot is assigned N-2
+ * etc.
  *
  * Placeholder slots:
  * In most cases, @pci_bus, @slot_nr will be sufficient to uniquely identify
@@ -99,62 +180,67 @@ static struct kobj_type pci_slot_ktype = {
  * the slot. In this scenario, the caller may pass -1 for @slot_nr.
  *
  * The following semantics are imposed when the caller passes @slot_nr ==
- * -1. First, the check for existing %struct pci_slot is skipped, as the
- * caller may know about several unpopulated slots on a given %struct
- * pci_bus, and each slot would have a @slot_nr of -1.  Uniqueness for
- * these slots is then determined by the @name parameter. We expect
- * kobject_init_and_add() to warn us if the caller attempts to create
- * multiple slots with the same name. The other change in semantics is
+ * -1. First, we no longer check for an existing %struct pci_slot, as there
+ * may be many slots with @slot_nr of -1.  The other change in semantics is
  * user-visible, which is the 'address' parameter presented in sysfs will
  * consist solely of a dddd:bb tuple, where dddd is the PCI domain of the
  * %struct pci_bus and bb is the bus number. In other words, the devfn of
  * the 'placeholder' slot will not be displayed.
  */
-
 struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr,
 				 const char *name,
 				 struct hotplug_slot *hotplug)
 {
 	struct pci_dev *dev;
 	struct pci_slot *slot;
-	int err;
+	int err = 0;
+	char *slot_name = NULL;
 
 	down_write(&pci_bus_sem);
 
 	if (slot_nr == -1)
 		goto placeholder;
 
-	/* If we've already created this slot, bump refcount and return. */
-	list_for_each_entry(slot, &parent->slots, list) {
-		if (slot->number == slot_nr) {
-			kobject_get(&slot->kobj);
-			pr_debug("%s: inc refcount to %d on %04x:%02x:%02x\n",
-				 __func__,
-				 atomic_read(&slot->kobj.kref.refcount),
-				 pci_domain_nr(parent), parent->number,
-				 slot_nr);
-			goto out;
+	/*
+	 * Hotplug drivers are allowed to rename an existing slot,
+	 * but only if not already claimed.
+	 */
+	slot = get_slot(parent, slot_nr);
+	if (slot) {
+		if (hotplug) {
+			if ((err = slot->hotplug ? -EBUSY : 0)
+			     || (err = rename_slot(slot, name))) {
+				kobject_put(&slot->kobj);
+				slot = NULL;
+				goto err;
+			}
 		}
+		goto out;
 	}
 
 placeholder:
 	slot = kzalloc(sizeof(*slot), GFP_KERNEL);
 	if (!slot) {
-		slot = ERR_PTR(-ENOMEM);
-		goto out;
+		err = -ENOMEM;
+		goto err;
 	}
 
 	slot->bus = parent;
 	slot->number = slot_nr;
 
 	slot->kobj.kset = pci_slots_kset;
-	err = kobject_init_and_add(&slot->kobj, &pci_slot_ktype, NULL,
-				   "%s", name);
-	if (err) {
-		printk(KERN_ERR "Unable to register kobject %s\n", name);
+
+	slot_name = make_slot_name(name);
+	if (!slot_name) {
+		err = -ENOMEM;
 		goto err;
 	}
 
+	err = kobject_init_and_add(&slot->kobj, &pci_slot_ktype, NULL,
+				   "%s", slot_name);
+	if (err)
+		goto err;
+
 	INIT_LIST_HEAD(&slot->list);
 	list_add(&slot->list, &parent->slots);
 
@@ -166,10 +252,10 @@ placeholder:
 	pr_debug("%s: created pci_slot on %04x:%02x:%02x\n",
 		 __func__, pci_domain_nr(parent), parent->number, slot_nr);
 
- out:
+out:
 	up_write(&pci_bus_sem);
 	return slot;
- err:
+err:
 	kfree(slot);
 	slot = ERR_PTR(err);
 	goto out;
@@ -210,7 +296,6 @@ EXPORT_SYMBOL_GPL(pci_renumber_slot);
  * just call kobject_put on its kobj and let our release methods do the
  * rest.
  */
-
 void pci_destroy_slot(struct pci_slot *slot)
 {
 	pr_debug("%s: dec refcount to %d on %04x:%02x:%02x\n", __func__,