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linux/drivers/pci/hotplug/acpiphp_core.c
Lukas Wunner 51bbf9bee3 PCI: hotplug: Demidlayer registration with the core 
When a hotplug driver calls pci_hp_register(), all steps necessary for
registration are carried out in one go, including creation of a kobject
and addition to sysfs.  That's a problem for pciehp once it's converted
to enable/disable the slot exclusively from the IRQ thread:  The thread
needs to be spawned after creation of the kobject (because it uses the
kobject's name), but before addition to sysfs (because it will handle
enable/disable requests submitted via sysfs).

pci_hp_deregister() does offer a ->release callback that's invoked
after deletion from sysfs and before destruction of the kobject.  But
because pci_hp_register() doesn't offer a counterpart, hotplug drivers'
->probe and ->remove code becomes asymmetric, which is error prone
as recently discovered use-after-free bugs in pciehp's ->remove hook
have shown.

In a sense, this appears to be a case of the midlayer antipattern:

   "The core thesis of the "midlayer mistake" is that midlayers are
    bad and should not exist.  That common functionality which it is
    so tempting to put in a midlayer should instead be provided as
    library routines which can [be] used, augmented, or ignored by
    each bottom level driver independently.  Thus every subsystem
    that supports multiple implementations (or drivers) should
    provide a very thin top layer which calls directly into the
    bottom layer drivers, and a rich library of support code that
    eases the implementation of those drivers.  This library is
    available to, but not forced upon, those drivers."
        --  Neil Brown (2009), https://lwn.net/Articles/336262/

The presence of midlayer traits in the PCI hotplug core might be ascribed
to its age:  When it was introduced in February 2002, the blessings of a
library approach might not have been well known:
https://git.kernel.org/tglx/history/c/a8a2069f432c

For comparison, the driver core does offer split functions for creating
a kobject (device_initialize()) and addition to sysfs (device_add()) as
an alternative to carrying out everything at once (device_register()).
This was introduced in October 2002:
https://git.kernel.org/tglx/history/c/8b290eb19962

The odd ->release callback in the PCI hotplug core was added in 2003:
https://git.kernel.org/tglx/history/c/69f8d663b595

Clearly, a library approach would not force every hotplug driver to
implement a ->release callback, but rather allow the driver to remove
the sysfs files, release its data structures and finally destroy the
kobject.  Alternatively, a driver may choose to remove everything with
pci_hp_deregister(), then release its data structures.

To this end, offer drivers pci_hp_initialize() and pci_hp_add() as a
split-up version of pci_hp_register().  Likewise, offer pci_hp_del()
and pci_hp_destroy() as a split-up version of pci_hp_deregister().

Eliminate the ->release callback and move its code into each driver's
teardown routine.

Declare pci_hp_deregister() void, in keeping with the usual kernel
pattern that enablement can fail, but disablement cannot.  It only
returned an error if the caller passed in a NULL pointer or a slot which
has never or is no longer registered or is sharing its name with another
slot.  Those would be bugs, so WARN about them.  Few hotplug drivers
actually checked the return value and those that did only printed a
useless error message to dmesg.  Remove that.

For most drivers the conversion was straightforward since it doesn't
matter whether the code in the ->release callback is executed before or
after destruction of the kobject.  But in the case of ibmphp, it was
unclear to me whether setting slot_cur->ctrl and slot_cur->bus_on to
NULL needs to happen before the kobject is destroyed, so I erred on
the side of caution and ensured that the order stays the same.  Another
nontrivial case is pnv_php, I've found the list and kref logic difficult
to understand, however my impression was that it is safe to delete the
list element and drop the references until after the kobject is
destroyed.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com>  # drivers/platform/x86
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Len Brown <lenb@kernel.org>
Cc: Scott Murray <scott@spiteful.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Gavin Shan <gwshan@linux.vnet.ibm.com>
Cc: Sebastian Ott <sebott@linux.vnet.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: Corentin Chary <corentin.chary@gmail.com>
Cc: Darren Hart <dvhart@infradead.org>
Cc: Andy Shevchenko <andy@infradead.org>
2018-07-23 17:04:13 -05:00

327 lines
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// SPDX-License-Identifier: GPL-2.0+
/*
* ACPI PCI Hot Plug Controller Driver
*
* Copyright (C) 1995,2001 Compaq Computer Corporation
* Copyright (C) 2001 Greg Kroah-Hartman (greg@kroah.com)
* Copyright (C) 2001 IBM Corp.
* Copyright (C) 2002 Hiroshi Aono (h-aono@ap.jp.nec.com)
* Copyright (C) 2002,2003 Takayoshi Kochi (t-kochi@bq.jp.nec.com)
* Copyright (C) 2002,2003 NEC Corporation
* Copyright (C) 2003-2005 Matthew Wilcox (matthew.wilcox@hp.com)
* Copyright (C) 2003-2005 Hewlett Packard
*
* All rights reserved.
*
* Send feedback to <kristen.c.accardi@intel.com>
*
*/
#define pr_fmt(fmt) "acpiphp: " fmt
#include <linux/init.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/kernel.h>
#include <linux/pci.h>
#include <linux/pci-acpi.h>
#include <linux/pci_hotplug.h>
#include <linux/slab.h>
#include <linux/smp.h>
#include "acpiphp.h"
/* name size which is used for entries in pcihpfs */
#define SLOT_NAME_SIZE 21 /* {_SUN} */
bool acpiphp_disabled;
/* local variables */
static struct acpiphp_attention_info *attention_info;
#define DRIVER_VERSION "0.5"
#define DRIVER_AUTHOR "Greg Kroah-Hartman <gregkh@us.ibm.com>, Takayoshi Kochi <t-kochi@bq.jp.nec.com>, Matthew Wilcox <willy@hp.com>"
#define DRIVER_DESC "ACPI Hot Plug PCI Controller Driver"
MODULE_AUTHOR(DRIVER_AUTHOR);
MODULE_DESCRIPTION(DRIVER_DESC);
MODULE_LICENSE("GPL");
MODULE_PARM_DESC(disable, "disable acpiphp driver");
module_param_named(disable, acpiphp_disabled, bool, 0444);
static int enable_slot(struct hotplug_slot *slot);
static int disable_slot(struct hotplug_slot *slot);
static int set_attention_status(struct hotplug_slot *slot, u8 value);
static int get_power_status(struct hotplug_slot *slot, u8 *value);
static int get_attention_status(struct hotplug_slot *slot, u8 *value);
static int get_latch_status(struct hotplug_slot *slot, u8 *value);
static int get_adapter_status(struct hotplug_slot *slot, u8 *value);
static struct hotplug_slot_ops acpi_hotplug_slot_ops = {
.enable_slot = enable_slot,
.disable_slot = disable_slot,
.set_attention_status = set_attention_status,
.get_power_status = get_power_status,
.get_attention_status = get_attention_status,
.get_latch_status = get_latch_status,
.get_adapter_status = get_adapter_status,
};
/**
* acpiphp_register_attention - set attention LED callback
* @info: must be completely filled with LED callbacks
*
* Description: This is used to register a hardware specific ACPI
* driver that manipulates the attention LED. All the fields in
* info must be set.
*/
int acpiphp_register_attention(struct acpiphp_attention_info *info)
{
int retval = -EINVAL;
if (info && info->owner && info->set_attn &&
info->get_attn && !attention_info) {
retval = 0;
attention_info = info;
}
return retval;
}
EXPORT_SYMBOL_GPL(acpiphp_register_attention);
/**
* acpiphp_unregister_attention - unset attention LED callback
* @info: must match the pointer used to register
*
* Description: This is used to un-register a hardware specific acpi
* driver that manipulates the attention LED. The pointer to the
* info struct must be the same as the one used to set it.
*/
int acpiphp_unregister_attention(struct acpiphp_attention_info *info)
{
int retval = -EINVAL;
if (info && attention_info == info) {
attention_info = NULL;
retval = 0;
}
return retval;
}
EXPORT_SYMBOL_GPL(acpiphp_unregister_attention);
/**
* enable_slot - power on and enable a slot
* @hotplug_slot: slot to enable
*
* Actual tasks are done in acpiphp_enable_slot()
*/
static int enable_slot(struct hotplug_slot *hotplug_slot)
{
struct slot *slot = hotplug_slot->private;
pr_debug("%s - physical_slot = %s\n", __func__, slot_name(slot));
/* enable the specified slot */
return acpiphp_enable_slot(slot->acpi_slot);
}
/**
* disable_slot - disable and power off a slot
* @hotplug_slot: slot to disable
*
* Actual tasks are done in acpiphp_disable_slot()
*/
static int disable_slot(struct hotplug_slot *hotplug_slot)
{
struct slot *slot = hotplug_slot->private;
pr_debug("%s - physical_slot = %s\n", __func__, slot_name(slot));
/* disable the specified slot */
return acpiphp_disable_slot(slot->acpi_slot);
}
/**
* set_attention_status - set attention LED
* @hotplug_slot: slot to set attention LED on
* @status: value to set attention LED to (0 or 1)
*
* attention status LED, so we use a callback that
* was registered with us. This allows hardware specific
* ACPI implementations to blink the light for us.
*/
static int set_attention_status(struct hotplug_slot *hotplug_slot, u8 status)
{
int retval = -ENODEV;
pr_debug("%s - physical_slot = %s\n", __func__,
hotplug_slot_name(hotplug_slot));
if (attention_info && try_module_get(attention_info->owner)) {
retval = attention_info->set_attn(hotplug_slot, status);
module_put(attention_info->owner);
} else
attention_info = NULL;
return retval;
}
/**
* get_power_status - get power status of a slot
* @hotplug_slot: slot to get status
* @value: pointer to store status
*
* Some platforms may not implement _STA method properly.
* In that case, the value returned may not be reliable.
*/
static int get_power_status(struct hotplug_slot *hotplug_slot, u8 *value)
{
struct slot *slot = hotplug_slot->private;
pr_debug("%s - physical_slot = %s\n", __func__, slot_name(slot));
*value = acpiphp_get_power_status(slot->acpi_slot);
return 0;
}
/**
* get_attention_status - get attention LED status
* @hotplug_slot: slot to get status from
* @value: returns with value of attention LED
*
* ACPI doesn't have known method to determine the state
* of the attention status LED, so we use a callback that
* was registered with us. This allows hardware specific
* ACPI implementations to determine its state.
*/
static int get_attention_status(struct hotplug_slot *hotplug_slot, u8 *value)
{
int retval = -EINVAL;
pr_debug("%s - physical_slot = %s\n", __func__,
hotplug_slot_name(hotplug_slot));
if (attention_info && try_module_get(attention_info->owner)) {
retval = attention_info->get_attn(hotplug_slot, value);
module_put(attention_info->owner);
} else
attention_info = NULL;
return retval;
}
/**
* get_latch_status - get latch status of a slot
* @hotplug_slot: slot to get status
* @value: pointer to store status
*
* ACPI doesn't provide any formal means to access latch status.
* Instead, we fake latch status from _STA.
*/
static int get_latch_status(struct hotplug_slot *hotplug_slot, u8 *value)
{
struct slot *slot = hotplug_slot->private;
pr_debug("%s - physical_slot = %s\n", __func__, slot_name(slot));
*value = acpiphp_get_latch_status(slot->acpi_slot);
return 0;
}
/**
* get_adapter_status - get adapter status of a slot
* @hotplug_slot: slot to get status
* @value: pointer to store status
*
* ACPI doesn't provide any formal means to access adapter status.
* Instead, we fake adapter status from _STA.
*/
static int get_adapter_status(struct hotplug_slot *hotplug_slot, u8 *value)
{
struct slot *slot = hotplug_slot->private;
pr_debug("%s - physical_slot = %s\n", __func__, slot_name(slot));
*value = acpiphp_get_adapter_status(slot->acpi_slot);
return 0;
}
/* callback routine to initialize 'struct slot' for each slot */
int acpiphp_register_hotplug_slot(struct acpiphp_slot *acpiphp_slot,
unsigned int sun)
{
struct slot *slot;
int retval = -ENOMEM;
char name[SLOT_NAME_SIZE];
slot = kzalloc(sizeof(*slot), GFP_KERNEL);
if (!slot)
goto error;
slot->hotplug_slot = kzalloc(sizeof(*slot->hotplug_slot), GFP_KERNEL);
if (!slot->hotplug_slot)
goto error_slot;
slot->hotplug_slot->info = &slot->info;
slot->hotplug_slot->private = slot;
slot->hotplug_slot->ops = &acpi_hotplug_slot_ops;
slot->acpi_slot = acpiphp_slot;
slot->hotplug_slot->info->power_status = acpiphp_get_power_status(slot->acpi_slot);
slot->hotplug_slot->info->attention_status = 0;
slot->hotplug_slot->info->latch_status = acpiphp_get_latch_status(slot->acpi_slot);
slot->hotplug_slot->info->adapter_status = acpiphp_get_adapter_status(slot->acpi_slot);
acpiphp_slot->slot = slot;
slot->sun = sun;
snprintf(name, SLOT_NAME_SIZE, "%u", sun);
retval = pci_hp_register(slot->hotplug_slot, acpiphp_slot->bus,
acpiphp_slot->device, name);
if (retval == -EBUSY)
goto error_hpslot;
if (retval) {
pr_err("pci_hp_register failed with error %d\n", retval);
goto error_hpslot;
}
pr_info("Slot [%s] registered\n", slot_name(slot));
return 0;
error_hpslot:
kfree(slot->hotplug_slot);
error_slot:
kfree(slot);
error:
return retval;
}
void acpiphp_unregister_hotplug_slot(struct acpiphp_slot *acpiphp_slot)
{
struct slot *slot = acpiphp_slot->slot;
pr_info("Slot [%s] unregistered\n", slot_name(slot));
pci_hp_deregister(slot->hotplug_slot);
kfree(slot->hotplug_slot);
kfree(slot);
}
void __init acpiphp_init(void)
{
pr_info(DRIVER_DESC " version: " DRIVER_VERSION "%s\n",
acpiphp_disabled ? ", disabled by user; please report a bug"
: "");
}
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