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b4ffb19098
linux/drivers/watchdog/watchdog_dev.c
Guenter Roeck b4ffb19098 watchdog: Separate and maintain variables based on variable lifetime 
All variables required by the watchdog core to manage a watchdog are
currently stored in struct watchdog_device. The lifetime of those
variables is determined by the watchdog driver. However, the lifetime
of variables used by the watchdog core differs from the lifetime of
struct watchdog_device. To remedy this situation, watchdog drivers
can implement ref and unref callbacks, to be used by the watchdog
core to lock struct watchdog_device in memory.

While this solves the immediate problem, it depends on watchdog drivers
to actually implement the ref/unref callbacks. This is error prone,
often not implemented in the first place, or not implemented correctly.

To solve the problem without requiring driver support, split the variables
in struct watchdog_device into two data structures - one for variables
associated with the watchdog driver, one for variables associated with
the watchdog core. With this approach, the watchdog core can keep track
of its variable lifetime and no longer depends on ref/unref callbacks
in the driver. As a side effect, some of the variables originally in
struct watchdog_driver are now private to the watchdog core and no longer
visible in watchdog drivers.

As a side effect of the changes made, an ioctl will now always fail
with -ENODEV after a watchdog device was unregistered with the character
device still open. Previously, it would only fail with -ENODEV in some
situations. Also, ioctl operations are now atomic from driver perspective.
With this change, it is now guaranteed that the driver will not unregister
a watchdog between a timeout change and the subsequent ping.

The 'ref' and 'unref' callbacks in struct watchdog_driver are no longer
used and marked as deprecated.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
2015-12-29 20:36:03 +01:00

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/*
* watchdog_dev.c
*
* (c) Copyright 2008-2011 Alan Cox <alan@lxorguk.ukuu.org.uk>,
* All Rights Reserved.
*
* (c) Copyright 2008-2011 Wim Van Sebroeck <wim@iguana.be>.
*
*
* This source code is part of the generic code that can be used
* by all the watchdog timer drivers.
*
* This part of the generic code takes care of the following
* misc device: /dev/watchdog.
*
* Based on source code of the following authors:
* Matt Domsch <Matt_Domsch@dell.com>,
* Rob Radez <rob@osinvestor.com>,
* Rusty Lynch <rusty@linux.co.intel.com>
* Satyam Sharma <satyam@infradead.org>
* Randy Dunlap <randy.dunlap@oracle.com>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*
* Neither Alan Cox, CymruNet Ltd., Wim Van Sebroeck nor Iguana vzw.
* admit liability nor provide warranty for any of this software.
* This material is provided "AS-IS" and at no charge.
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/cdev.h> /* For character device */
#include <linux/errno.h> /* For the -ENODEV/... values */
#include <linux/fs.h> /* For file operations */
#include <linux/init.h> /* For __init/__exit/... */
#include <linux/kernel.h> /* For printk/panic/... */
#include <linux/kref.h> /* For data references */
#include <linux/miscdevice.h> /* For handling misc devices */
#include <linux/module.h> /* For module stuff/... */
#include <linux/mutex.h> /* For mutexes */
#include <linux/slab.h> /* For memory functions */
#include <linux/types.h> /* For standard types (like size_t) */
#include <linux/watchdog.h> /* For watchdog specific items */
#include <linux/uaccess.h> /* For copy_to_user/put_user/... */
#include "watchdog_core.h"
/*
* struct watchdog_core_data - watchdog core internal data
* @kref: Reference count.
* @cdev: The watchdog's Character device.
* @wdd: Pointer to watchdog device.
* @lock: Lock for watchdog core.
* @status: Watchdog core internal status bits.
*/
struct watchdog_core_data {
struct kref kref;
struct cdev cdev;
struct watchdog_device *wdd;
struct mutex lock;
unsigned long status; /* Internal status bits */
#define _WDOG_DEV_OPEN 0 /* Opened ? */
#define _WDOG_ALLOW_RELEASE 1 /* Did we receive the magic char ? */
};
/* the dev_t structure to store the dynamically allocated watchdog devices */
static dev_t watchdog_devt;
/* Reference to watchdog device behind /dev/watchdog */
static struct watchdog_core_data *old_wd_data;
/*
* watchdog_ping: ping the watchdog.
* @wdd: the watchdog device to ping
*
* The caller must hold wd_data->lock.
*
* If the watchdog has no own ping operation then it needs to be
* restarted via the start operation. This wrapper function does
* exactly that.
* We only ping when the watchdog device is running.
*/
static int watchdog_ping(struct watchdog_device *wdd)
{
int err;
if (!watchdog_active(wdd))
return 0;
if (wdd->ops->ping)
err = wdd->ops->ping(wdd); /* ping the watchdog */
else
err = wdd->ops->start(wdd); /* restart watchdog */
return err;
}
/*
* watchdog_start: wrapper to start the watchdog.
* @wdd: the watchdog device to start
*
* The caller must hold wd_data->lock.
*
* Start the watchdog if it is not active and mark it active.
* This function returns zero on success or a negative errno code for
* failure.
*/
static int watchdog_start(struct watchdog_device *wdd)
{
int err;
if (watchdog_active(wdd))
return 0;
err = wdd->ops->start(wdd);
if (err == 0)
set_bit(WDOG_ACTIVE, &wdd->status);
return err;
}
/*
* watchdog_stop: wrapper to stop the watchdog.
* @wdd: the watchdog device to stop
*
* The caller must hold wd_data->lock.
*
* Stop the watchdog if it is still active and unmark it active.
* This function returns zero on success or a negative errno code for
* failure.
* If the 'nowayout' feature was set, the watchdog cannot be stopped.
*/
static int watchdog_stop(struct watchdog_device *wdd)
{
int err;
if (!watchdog_active(wdd))
return 0;
if (test_bit(WDOG_NO_WAY_OUT, &wdd->status)) {
dev_info(wdd->dev, "nowayout prevents watchdog being stopped!\n");
return -EBUSY;
}
err = wdd->ops->stop(wdd);
if (err == 0)
clear_bit(WDOG_ACTIVE, &wdd->status);
return err;
}
/*
* watchdog_get_status: wrapper to get the watchdog status
* @wdd: the watchdog device to get the status from
*
* The caller must hold wd_data->lock.
*
* Get the watchdog's status flags.
*/
static unsigned int watchdog_get_status(struct watchdog_device *wdd)
{
if (!wdd->ops->status)
return 0;
return wdd->ops->status(wdd);
}
/*
* watchdog_set_timeout: set the watchdog timer timeout
* @wdd: the watchdog device to set the timeout for
* @timeout: timeout to set in seconds
*
* The caller must hold wd_data->lock.
*/
static int watchdog_set_timeout(struct watchdog_device *wdd,
unsigned int timeout)
{
if (!wdd->ops->set_timeout || !(wdd->info->options & WDIOF_SETTIMEOUT))
return -EOPNOTSUPP;
if (watchdog_timeout_invalid(wdd, timeout))
return -EINVAL;
return wdd->ops->set_timeout(wdd, timeout);
}
/*
* watchdog_get_timeleft: wrapper to get the time left before a reboot
* @wdd: the watchdog device to get the remaining time from
* @timeleft: the time that's left
*
* The caller must hold wd_data->lock.
*
* Get the time before a watchdog will reboot (if not pinged).
*/
static int watchdog_get_timeleft(struct watchdog_device *wdd,
unsigned int *timeleft)
{
*timeleft = 0;
if (!wdd->ops->get_timeleft)
return -EOPNOTSUPP;
*timeleft = wdd->ops->get_timeleft(wdd);
return 0;
}
#ifdef CONFIG_WATCHDOG_SYSFS
static ssize_t nowayout_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
struct watchdog_device *wdd = dev_get_drvdata(dev);
return sprintf(buf, "%d\n", !!test_bit(WDOG_NO_WAY_OUT, &wdd->status));
}
static DEVICE_ATTR_RO(nowayout);
static ssize_t status_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
struct watchdog_device *wdd = dev_get_drvdata(dev);
struct watchdog_core_data *wd_data = wdd->wd_data;
unsigned int status;
mutex_lock(&wd_data->lock);
status = watchdog_get_status(wdd);
mutex_unlock(&wd_data->lock);
return sprintf(buf, "%u\n", status);
}
static DEVICE_ATTR_RO(status);
static ssize_t bootstatus_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct watchdog_device *wdd = dev_get_drvdata(dev);
return sprintf(buf, "%u\n", wdd->bootstatus);
}
static DEVICE_ATTR_RO(bootstatus);
static ssize_t timeleft_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
struct watchdog_device *wdd = dev_get_drvdata(dev);
struct watchdog_core_data *wd_data = wdd->wd_data;
ssize_t status;
unsigned int val;
mutex_lock(&wd_data->lock);
status = watchdog_get_timeleft(wdd, &val);
mutex_unlock(&wd_data->lock);
if (!status)
status = sprintf(buf, "%u\n", val);
return status;
}
static DEVICE_ATTR_RO(timeleft);
static ssize_t timeout_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
struct watchdog_device *wdd = dev_get_drvdata(dev);
return sprintf(buf, "%u\n", wdd->timeout);
}
static DEVICE_ATTR_RO(timeout);
static ssize_t identity_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
struct watchdog_device *wdd = dev_get_drvdata(dev);
return sprintf(buf, "%s\n", wdd->info->identity);
}
static DEVICE_ATTR_RO(identity);
static ssize_t state_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
struct watchdog_device *wdd = dev_get_drvdata(dev);
if (watchdog_active(wdd))
return sprintf(buf, "active\n");
return sprintf(buf, "inactive\n");
}
static DEVICE_ATTR_RO(state);
static umode_t wdt_is_visible(struct kobject *kobj, struct attribute *attr,
int n)
{
struct device *dev = container_of(kobj, struct device, kobj);
struct watchdog_device *wdd = dev_get_drvdata(dev);
umode_t mode = attr->mode;
if (attr == &dev_attr_status.attr && !wdd->ops->status)
mode = 0;
else if (attr == &dev_attr_timeleft.attr && !wdd->ops->get_timeleft)
mode = 0;
return mode;
}
static struct attribute *wdt_attrs[] = {
&dev_attr_state.attr,
&dev_attr_identity.attr,
&dev_attr_timeout.attr,
&dev_attr_timeleft.attr,
&dev_attr_bootstatus.attr,
&dev_attr_status.attr,
&dev_attr_nowayout.attr,
NULL,
};
static const struct attribute_group wdt_group = {
.attrs = wdt_attrs,
.is_visible = wdt_is_visible,
};
__ATTRIBUTE_GROUPS(wdt);
#else
#define wdt_groups NULL
#endif
/*
* watchdog_ioctl_op: call the watchdog drivers ioctl op if defined
* @wdd: the watchdog device to do the ioctl on
* @cmd: watchdog command
* @arg: argument pointer
*
* The caller must hold wd_data->lock.
*/
static int watchdog_ioctl_op(struct watchdog_device *wdd, unsigned int cmd,
unsigned long arg)
{
if (!wdd->ops->ioctl)
return -ENOIOCTLCMD;
return wdd->ops->ioctl(wdd, cmd, arg);
}
/*
* watchdog_write: writes to the watchdog.
* @file: file from VFS
* @data: user address of data
* @len: length of data
* @ppos: pointer to the file offset
*
* A write to a watchdog device is defined as a keepalive ping.
* Writing the magic 'V' sequence allows the next close to turn
* off the watchdog (if 'nowayout' is not set).
*/
static ssize_t watchdog_write(struct file *file, const char __user *data,
size_t len, loff_t *ppos)
{
struct watchdog_core_data *wd_data = file->private_data;
struct watchdog_device *wdd;
int err;
size_t i;
char c;
if (len == 0)
return 0;
/*
* Note: just in case someone wrote the magic character
* five months ago...
*/
clear_bit(_WDOG_ALLOW_RELEASE, &wd_data->status);
/* scan to see whether or not we got the magic character */
for (i = 0; i != len; i++) {
if (get_user(c, data + i))
return -EFAULT;
if (c == 'V')
set_bit(_WDOG_ALLOW_RELEASE, &wd_data->status);
}
/* someone wrote to us, so we send the watchdog a keepalive ping */
err = -ENODEV;
mutex_lock(&wd_data->lock);
wdd = wd_data->wdd;
if (wdd)
err = watchdog_ping(wdd);
mutex_unlock(&wd_data->lock);
if (err < 0)
return err;
return len;
}
/*
* watchdog_ioctl: handle the different ioctl's for the watchdog device.
* @file: file handle to the device
* @cmd: watchdog command
* @arg: argument pointer
*
* The watchdog API defines a common set of functions for all watchdogs
* according to their available features.
*/
static long watchdog_ioctl(struct file *file, unsigned int cmd,
unsigned long arg)
{
struct watchdog_core_data *wd_data = file->private_data;
void __user *argp = (void __user *)arg;
struct watchdog_device *wdd;
int __user *p = argp;
unsigned int val;
int err;
mutex_lock(&wd_data->lock);
wdd = wd_data->wdd;
if (!wdd) {
err = -ENODEV;
goto out_ioctl;
}
err = watchdog_ioctl_op(wdd, cmd, arg);
if (err != -ENOIOCTLCMD)
goto out_ioctl;
switch (cmd) {
case WDIOC_GETSUPPORT:
err = copy_to_user(argp, wdd->info,
sizeof(struct watchdog_info)) ? -EFAULT : 0;
break;
case WDIOC_GETSTATUS:
val = watchdog_get_status(wdd);
err = put_user(val, p);
break;
case WDIOC_GETBOOTSTATUS:
err = put_user(wdd->bootstatus, p);
break;
case WDIOC_SETOPTIONS:
if (get_user(val, p)) {
err = -EFAULT;
break;
}
if (val & WDIOS_DISABLECARD) {
err = watchdog_stop(wdd);
if (err < 0)
break;
}
if (val & WDIOS_ENABLECARD)
err = watchdog_start(wdd);
break;
case WDIOC_KEEPALIVE:
if (!(wdd->info->options & WDIOF_KEEPALIVEPING)) {
err = -EOPNOTSUPP;
break;
}
err = watchdog_ping(wdd);
break;
case WDIOC_SETTIMEOUT:
if (get_user(val, p)) {
err = -EFAULT;
break;
}
err = watchdog_set_timeout(wdd, val);
if (err < 0)
break;
/* If the watchdog is active then we send a keepalive ping
* to make sure that the watchdog keep's running (and if
* possible that it takes the new timeout) */
err = watchdog_ping(wdd);
if (err < 0)
break;
/* Fall */
case WDIOC_GETTIMEOUT:
/* timeout == 0 means that we don't know the timeout */
if (wdd->timeout == 0) {
err = -EOPNOTSUPP;
break;
}
err = put_user(wdd->timeout, p);
break;
case WDIOC_GETTIMELEFT:
err = watchdog_get_timeleft(wdd, &val);
if (err < 0)
break;
err = put_user(val, p);
break;
default:
err = -ENOTTY;
break;
}
out_ioctl:
mutex_unlock(&wd_data->lock);
return err;
}
/*
* watchdog_open: open the /dev/watchdog* devices.
* @inode: inode of device
* @file: file handle to device
*
* When the /dev/watchdog* device gets opened, we start the watchdog.
* Watch out: the /dev/watchdog device is single open, so we make sure
* it can only be opened once.
*/
static int watchdog_open(struct inode *inode, struct file *file)
{
struct watchdog_core_data *wd_data;
struct watchdog_device *wdd;
int err;
/* Get the corresponding watchdog device */
if (imajor(inode) == MISC_MAJOR)
wd_data = old_wd_data;
else
wd_data = container_of(inode->i_cdev, struct watchdog_core_data,
cdev);
/* the watchdog is single open! */
if (test_and_set_bit(_WDOG_DEV_OPEN, &wd_data->status))
return -EBUSY;
wdd = wd_data->wdd;
/*
* If the /dev/watchdog device is open, we don't want the module
* to be unloaded.
*/
if (!try_module_get(wdd->ops->owner)) {
err = -EBUSY;
goto out_clear;
}
err = watchdog_start(wdd);
if (err < 0)
goto out_mod;
file->private_data = wd_data;
kref_get(&wd_data->kref);
/* dev/watchdog is a virtual (and thus non-seekable) filesystem */
return nonseekable_open(inode, file);
out_mod:
module_put(wd_data->wdd->ops->owner);
out_clear:
clear_bit(_WDOG_DEV_OPEN, &wd_data->status);
return err;
}
static void watchdog_core_data_release(struct kref *kref)
{
struct watchdog_core_data *wd_data;
wd_data = container_of(kref, struct watchdog_core_data, kref);
kfree(wd_data);
}
/*
* watchdog_release: release the watchdog device.
* @inode: inode of device
* @file: file handle to device
*
* This is the code for when /dev/watchdog gets closed. We will only
* stop the watchdog when we have received the magic char (and nowayout
* was not set), else the watchdog will keep running.
*/
static int watchdog_release(struct inode *inode, struct file *file)
{
struct watchdog_core_data *wd_data = file->private_data;
struct watchdog_device *wdd;
int err = -EBUSY;
mutex_lock(&wd_data->lock);
wdd = wd_data->wdd;
if (!wdd)
goto done;
/*
* We only stop the watchdog if we received the magic character
* or if WDIOF_MAGICCLOSE is not set. If nowayout was set then
* watchdog_stop will fail.
*/
if (!test_bit(WDOG_ACTIVE, &wdd->status))
err = 0;
else if (test_and_clear_bit(_WDOG_ALLOW_RELEASE, &wd_data->status) ||
!(wdd->info->options & WDIOF_MAGICCLOSE))
err = watchdog_stop(wdd);
/* If the watchdog was not stopped, send a keepalive ping */
if (err < 0) {
dev_crit(wdd->dev, "watchdog did not stop!\n");
watchdog_ping(wdd);
}
/* make sure that /dev/watchdog can be re-opened */
clear_bit(_WDOG_DEV_OPEN, &wd_data->status);
done:
mutex_unlock(&wd_data->lock);
/* Allow the owner module to be unloaded again */
module_put(wd_data->cdev.owner);
kref_put(&wd_data->kref, watchdog_core_data_release);
return 0;
}
static const struct file_operations watchdog_fops = {
.owner = THIS_MODULE,
.write = watchdog_write,
.unlocked_ioctl = watchdog_ioctl,
.open = watchdog_open,
.release = watchdog_release,
};
static struct miscdevice watchdog_miscdev = {
.minor = WATCHDOG_MINOR,
.name = "watchdog",
.fops = &watchdog_fops,
};
/*
* watchdog_cdev_register: register watchdog character device
* @wdd: watchdog device
* @devno: character device number
*
* Register a watchdog character device including handling the legacy
* /dev/watchdog node. /dev/watchdog is actually a miscdevice and
* thus we set it up like that.
*/
static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno)
{
struct watchdog_core_data *wd_data;
int err;
wd_data = kzalloc(sizeof(struct watchdog_core_data), GFP_KERNEL);
if (!wd_data)
return -ENOMEM;
kref_init(&wd_data->kref);
mutex_init(&wd_data->lock);
wd_data->wdd = wdd;
wdd->wd_data = wd_data;
if (wdd->id == 0) {
old_wd_data = wd_data;
watchdog_miscdev.parent = wdd->parent;
err = misc_register(&watchdog_miscdev);
if (err != 0) {
pr_err("%s: cannot register miscdev on minor=%d (err=%d).\n",
wdd->info->identity, WATCHDOG_MINOR, err);
if (err == -EBUSY)
pr_err("%s: a legacy watchdog module is probably present.\n",
wdd->info->identity);
old_wd_data = NULL;
kfree(wd_data);
return err;
}
}
/* Fill in the data structures */
cdev_init(&wd_data->cdev, &watchdog_fops);
wd_data->cdev.owner = wdd->ops->owner;
/* Add the device */
err = cdev_add(&wd_data->cdev, devno, 1);
if (err) {
pr_err("watchdog%d unable to add device %d:%d\n",
wdd->id, MAJOR(watchdog_devt), wdd->id);
if (wdd->id == 0) {
misc_deregister(&watchdog_miscdev);
old_wd_data = NULL;
kref_put(&wd_data->kref, watchdog_core_data_release);
}
}
return err;
}
/*
* watchdog_cdev_unregister: unregister watchdog character device
* @watchdog: watchdog device
*
* Unregister watchdog character device and if needed the legacy
* /dev/watchdog device.
*/
static void watchdog_cdev_unregister(struct watchdog_device *wdd)
{
struct watchdog_core_data *wd_data = wdd->wd_data;
cdev_del(&wd_data->cdev);
if (wdd->id == 0) {
misc_deregister(&watchdog_miscdev);
old_wd_data = NULL;
}
mutex_lock(&wd_data->lock);
wd_data->wdd = NULL;
wdd->wd_data = NULL;
mutex_unlock(&wd_data->lock);
kref_put(&wd_data->kref, watchdog_core_data_release);
}
static struct class watchdog_class = {
.name = "watchdog",
.owner = THIS_MODULE,
.dev_groups = wdt_groups,
};
/*
* watchdog_dev_register: register a watchdog device
* @wdd: watchdog device
*
* Register a watchdog device including handling the legacy
* /dev/watchdog node. /dev/watchdog is actually a miscdevice and
* thus we set it up like that.
*/
int watchdog_dev_register(struct watchdog_device *wdd)
{
struct device *dev;
dev_t devno;
int ret;
devno = MKDEV(MAJOR(watchdog_devt), wdd->id);
ret = watchdog_cdev_register(wdd, devno);
if (ret)
return ret;
dev = device_create(&watchdog_class, wdd->parent, devno, wdd,
"watchdog%d", wdd->id);
if (IS_ERR(dev)) {
watchdog_cdev_unregister(wdd);
return PTR_ERR(dev);
}
wdd->dev = dev;
return ret;
}
/*
* watchdog_dev_unregister: unregister a watchdog device
* @watchdog: watchdog device
*
* Unregister watchdog device and if needed the legacy
* /dev/watchdog device.
*/
void watchdog_dev_unregister(struct watchdog_device *wdd)
{
device_destroy(&watchdog_class, wdd->dev->devt);
wdd->dev = NULL;
watchdog_cdev_unregister(wdd);
}
/*
* watchdog_dev_init: init dev part of watchdog core
*
* Allocate a range of chardev nodes to use for watchdog devices
*/
int __init watchdog_dev_init(void)
{
int err;
err = class_register(&watchdog_class);
if (err < 0) {
pr_err("couldn't register class\n");
return err;
}
err = alloc_chrdev_region(&watchdog_devt, 0, MAX_DOGS, "watchdog");
if (err < 0) {
pr_err("watchdog: unable to allocate char dev region\n");
class_unregister(&watchdog_class);
return err;
}
return 0;
}
/*
* watchdog_dev_exit: exit dev part of watchdog core
*
* Release the range of chardev nodes used for watchdog devices
*/
void __exit watchdog_dev_exit(void)
{
unregister_chrdev_region(watchdog_devt, MAX_DOGS);
class_unregister(&watchdog_class);
}
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