Re: [PATCH 02/13] PCI: prevent duplicate slot names

Kenji Kaneshige
2008-08-21T10:25:53Z

Hi Alex-san,

Thank you for updated patches and I'm sorry for delayed comment.
I reviewed your patch and I found two problems. Please see below.

Alex Chiang wrote:
> 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
> The Mth registered slot becomes N-M
>
> A side effect of this patch is that the error condition for when
> multiple drivers attempt to claim the same slot becomes much more
> prominent.
>
> In other words, the previous error condition returned for
> duplicate slot names (-EEXIST) masked the case when multiple
> drivers attempted to claim the same slot. Now, the -EBUSY return
> makes the true error more obvious.
>
> Finally, since we now prevent duplicate slot names, we remove
> the logic introduced by the following commits:
>
> pci hotplug core: add check of duplicate slot name
> a86161b3134465f072d965ca7508ec9c1e2e52c7
>
> pciehp: fix slot name
> 3800345f723fd130d50434d4717b99d4a9f383c8
>
> pciehp: add message about pciehp_slot_with_bus option
> 9e4f2e8d4ddb04ad16a3828cd9a369a5a5287009
>
> shpchp: fix slot name
> ef0ff95f136f0f2d035667af5d18b824609de320
>
> shpchp: add message about shpchp_slot_with_bus option
> b3bd307c628af2f0a581c42d5d7e4bcdbbf64b6a
>
> Cc: jbarnes@virtuousgeek.org
> Cc: kristen.c.accardi@intel.com
> Cc: matthew@wil.cx
> Cc: kaneshige.kenji@jp.fujitsu.com
> Signed-off-by: Alex Chiang <achiang@hp.com>
> ---
>
> drivers/pci/hotplug/pci_hotplug_core.c | 4 -
> drivers/pci/hotplug/pciehp.h | 1
> drivers/pci/hotplug/pciehp_core.c | 7 --
> drivers/pci/hotplug/pciehp_hpc.c | 6 --
> drivers/pci/hotplug/shpchp_core.c | 14 -----
> drivers/pci/slot.c | 93 +++++++++++++++++++++++++-------
> 6 files changed, 76 insertions(+), 49 deletions(-)
>
> diff --git a/drivers/pci/hotplug/pci_hotplug_core.c b/drivers/pci/hotplug/pci_hotplug_core.c
> index 96f274e..da5908f 100644
> --- a/drivers/pci/hotplug/pci_hotplug_core.c
> +++ b/drivers/pci/hotplug/pci_hotplug_core.c
> @@ -570,10 +570,6 @@ int pci_hp_register(struct hotplug_slot *slot, struct pci_bus *bus, int slot_nr,
> return -EINVAL;
> }
>
> - /* Check if we have already registered a slot with the same name. */
> - if (get_slot_from_name(name))
> - return -EEXIST;
> -
> /*
> * No problems if we call this interface from both ACPI_PCI_SLOT
> * driver and call it here again. If we've already created the
> diff --git a/drivers/pci/hotplug/pciehp.h b/drivers/pci/hotplug/pciehp.h
> index e3a1e7e..9e6cec6 100644
> --- a/drivers/pci/hotplug/pciehp.h
> +++ b/drivers/pci/hotplug/pciehp.h
> @@ -43,7 +43,6 @@ extern int pciehp_poll_mode;
> extern int pciehp_poll_time;
> extern int pciehp_debug;
> extern int pciehp_force;
> -extern int pciehp_slot_with_bus;
> extern struct workqueue_struct *pciehp_wq;
>
> #define dbg(format, arg...) \
> diff --git a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c
> index 5952315..bed77af 100644
> --- a/drivers/pci/hotplug/pciehp_core.c
> +++ b/drivers/pci/hotplug/pciehp_core.c
> @@ -41,7 +41,6 @@ int pciehp_debug;
> int pciehp_poll_mode;
> int pciehp_poll_time;
> int pciehp_force;
> -int pciehp_slot_with_bus;
> struct workqueue_struct *pciehp_wq;
>
> #define DRIVER_VERSION "0.4"
> @@ -56,12 +55,10 @@ module_param(pciehp_debug, bool, 0644);
> module_param(pciehp_poll_mode, bool, 0644);
> module_param(pciehp_poll_time, int, 0644);
> module_param(pciehp_force, bool, 0644);
> -module_param(pciehp_slot_with_bus, bool, 0644);
> MODULE_PARM_DESC(pciehp_debug, "Debugging mode enabled or not");
> MODULE_PARM_DESC(pciehp_poll_mode, "Using polling mechanism for hot-plug events or not");
> MODULE_PARM_DESC(pciehp_poll_time, "Polling mechanism frequency, in seconds");
> MODULE_PARM_DESC(pciehp_force, "Force pciehp, even if _OSC and OSHP are missing");
> -MODULE_PARM_DESC(pciehp_slot_with_bus, "Use bus number in the slot name");
>
> #define PCIE_MODULE_NAME "pciehp"
>
> @@ -226,10 +223,6 @@ static int init_slots(struct controller *ctrl)
> slot->name);
> if (retval) {
> err("pci_hp_register failed with error %d\n", retval);
> - if (retval == -EEXIST)
> - err("Failed to register slot because of name "
> - "collision. Try \'pciehp_slot_with_bus\' "
> - "module option.\n");
> goto error_info;
> }
> /* create additional sysfs entries */
> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
> index ad27e9e..43ff979 100644
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> @@ -1032,11 +1032,7 @@ static void pcie_shutdown_notification(struct controller *ctrl)
>
> static void make_slot_name(struct slot *slot)
> {
> - if (pciehp_slot_with_bus)
> - snprintf(slot->name, SLOT_NAME_SIZE, "%04d_%04d",
> - slot->bus, slot->number);
> - else
> - snprintf(slot->name, SLOT_NAME_SIZE, "%d", slot->number);
> + snprintf(slot->name, SLOT_NAME_SIZE, "%d", slot->number);
> }
>
> static int pcie_init_slot(struct controller *ctrl)
> diff --git a/drivers/pci/hotplug/shpchp_core.c b/drivers/pci/hotplug/shpchp_core.c
> index 7bc06c0..136d9ea 100644
> --- a/drivers/pci/hotplug/shpchp_core.c
> +++ b/drivers/pci/hotplug/shpchp_core.c
> @@ -39,7 +39,6 @@
> int shpchp_debug;
> int shpchp_poll_mode;
> int shpchp_poll_time;
> -static int shpchp_slot_with_bus;
> struct workqueue_struct *shpchp_wq;
>
> #define DRIVER_VERSION "0.4"
> @@ -53,11 +52,9 @@ MODULE_LICENSE("GPL");
> module_param(shpchp_debug, bool, 0644);
> module_param(shpchp_poll_mode, bool, 0644);
> module_param(shpchp_poll_time, int, 0644);
> -module_param(shpchp_slot_with_bus, bool, 0644);
> MODULE_PARM_DESC(shpchp_debug, "Debugging mode enabled or not");
> MODULE_PARM_DESC(shpchp_poll_mode, "Using polling mechanism for hot-plug events or not");
> MODULE_PARM_DESC(shpchp_poll_time, "Polling mechanism frequency, in seconds");
> -MODULE_PARM_DESC(shpchp_slot_with_bus, "Use bus number in the slot name");
>
> #define SHPC_MODULE_NAME "shpchp"
>
> @@ -101,12 +98,7 @@ static void release_slot(struct hotplug_slot *hotplug_slot)
>
> static void make_slot_name(struct slot *slot)
> {
> - if (shpchp_slot_with_bus)
> - snprintf(slot->hotplug_slot->name, SLOT_NAME_SIZE, "%04d_%04d",
> - slot->bus, slot->number);
> - else
> - snprintf(slot->hotplug_slot->name, SLOT_NAME_SIZE, "%d",
> - slot->number);
> + snprintf(slot->hotplug_slot->name, SLOT_NAME_SIZE, "%d", slot->number);
> }
>
> static int init_slots(struct controller *ctrl)
> @@ -162,10 +154,6 @@ static int init_slots(struct controller *ctrl)
> hotplug_slot->name);
> if (retval) {
> err("pci_hp_register failed with error %d\n", retval);
> - if (retval == -EEXIST)
> - err("Failed to register slot because of name "
> - "collision. Try \'shpchp_slot_with_bus\' "
> - "module option.\n");
> goto error_info;
> }
>
> diff --git a/drivers/pci/slot.c b/drivers/pci/slot.c
> index 7e5b85c..42f0e12 100644
> --- a/drivers/pci/slot.c
> +++ b/drivers/pci/slot.c
> @@ -73,6 +73,50 @@ 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, width, dup = 1;
> + struct kobject *dup_slot;
> +
> + new_name = kstrdup(name, GFP_KERNEL);
> + if (!new_name)
> + goto out;
> +
> + /*
> + * Start off allocating enough room for "name-X"
> + */
> + len = strlen(name) + 2;
> + width = 1;
> +
> +try_again:
> + dup_slot = kset_find_obj(pci_slots_kset, new_name);
> + if (!dup_slot)
> + goto out;
> +

The kset_find_obj() increments reference counter of specified kobject. So
we must call kobject_put() for 'dup_slot', otherwise it leaks reference
counter of 'dup_slot' kobject and the corresponding slot directory will
never be removed. Here is a sample to fix this problem.

dup_slot = kset_find_ojb(pci_slots_kset, new_name);
if (!dup_slot)
goto out;
kobject_put(dup_slot);
^^^^^^^^^^^^^^^^^^^^^^ Added this line

I found another problem in pci_hp_register() that would be more complex
to fix than above-mentioned problem. Here is a pci_hp_register() with
all of your patch applied.

int pci_hp_register(struct hotplug_slot *slot, struct pci_bus *bus, int slot_nr,
const char *name)
{
(snip...)

/*
* No problems if we call this interface from both ACPI_PCI_SLOT
* driver and call it here again. If we've already created the
* pci_slot, the interface will simply bump the refcount.
*/
pci_slot = pci_create_slot(bus, slot_nr, name);
if (IS_ERR(pci_slot))
return PTR_ERR(pci_slot);

if (pci_slot->hotplug) {
dbg("%s: already claimed\n", __func__);
pci_destroy_slot(pci_slot);
return -EBUSY;
}

slot->pci_slot = pci_slot;
pci_slot->hotplug = slot;

/*
* Allow pcihp drivers to override the ACPI_PCI_SLOT name.
*/
if (strcmp(kobject_name(&pci_slot->kobj), name)) {
result = kobject_rename(&pci_slot->kobj, name);
if (result) {
pci_destroy_slot(pci_slot);
return result;
}
}

(snip...)
}

If name duplication was detected in pci_create_slot(), it renames the
slot name like 'N-1' and return successfully. Even though slot's kobject
name was registered as 'N-1', 'name' array still have 'N' at this point.
So the following 'if' statement becomes true unexpectedly.

/*
* Allow pcihp drivers to override the ACPI_PCI_SLOT name.
*/
if (strcmp(kobject_name(&pci_slot->kobj), name)) {

Then pci_hp_register() attempt to rename the slot name with 'N' again
by calling kobject_rename(), but it fails because there already exists
kobject with name 'N'. As a result, pci_hp_register() will fail.

Thanks,
Kenji Kaneshige