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watchdog: Fix the race between the release of watchdog_core_data and …
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…cdev

[ Upstream commit 72139df ]

The struct cdev is embedded in the struct watchdog_core_data. In the
current code, we manage the watchdog_core_data with a kref, but the
cdev is manged by a kobject. There is no any relationship between
this kref and kobject. So it is possible that the watchdog_core_data is
freed before the cdev is entirely released. We can easily get the
following call trace with CONFIG_DEBUG_KOBJECT_RELEASE and
CONFIG_DEBUG_OBJECTS_TIMERS enabled.
  ODEBUG: free active (active state 0) object type: timer_list hint: delayed_work_timer_fn+0x0/0x38
  WARNING: CPU: 23 PID: 1028 at lib/debugobjects.c:481 debug_print_object+0xb0/0xf0
  Modules linked in: softdog(-) deflate ctr twofish_generic twofish_common camellia_generic serpent_generic blowfish_generic blowfish_common cast5_generic cast_common cmac xcbc af_key sch_fq_codel openvswitch nsh nf_conncount nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4
  CPU: 23 PID: 1028 Comm: modprobe Not tainted 5.3.0-next-20190924-yoctodev-standard+ torvalds#180
  Hardware name: Marvell OcteonTX CN96XX board (DT)
  pstate: 00400009 (nzcv daif +PAN -UAO)
  pc : debug_print_object+0xb0/0xf0
  lr : debug_print_object+0xb0/0xf0
  sp : ffff80001cbcfc70
  x29: ffff80001cbcfc70 x28: ffff800010ea2128
  x27: ffff800010bad000 x26: 0000000000000000
  x25: ffff80001103c640 x24: ffff80001107b268
  x23: ffff800010bad9e8 x22: ffff800010ea2128
  x21: ffff000bc2c62af8 x20: ffff80001103c600
  x19: ffff800010e867d8 x18: 0000000000000060
  x17: 0000000000000000 x16: 0000000000000000
  x15: ffff000bd7240470 x14: 6e6968207473696c
  x13: 5f72656d6974203a x12: 6570797420746365
  x11: 6a626f2029302065 x10: 7461747320657669
  x9 : 7463612820657669 x8 : 3378302f3078302b
  x7 : 0000000000001d7a x6 : ffff800010fd5889
  x5 : 0000000000000000 x4 : 0000000000000000
  x3 : 0000000000000000 x2 : ffff000bff948548
  x1 : 276a1c9e1edc2300 x0 : 0000000000000000
  Call trace:
   debug_print_object+0xb0/0xf0
   debug_check_no_obj_freed+0x1e8/0x210
   kfree+0x1b8/0x368
   watchdog_cdev_unregister+0x88/0xc8
   watchdog_dev_unregister+0x38/0x48
   watchdog_unregister_device+0xa8/0x100
   softdog_exit+0x18/0xfec4 [softdog]
   __arm64_sys_delete_module+0x174/0x200
   el0_svc_handler+0xd0/0x1c8
   el0_svc+0x8/0xc

This is a common issue when using cdev embedded in a struct.
Fortunately, we already have a mechanism to solve this kind of issue.
Please see commit 233ed09 ("chardev: add helper function to
register char devs with a struct device") for more detail.

In this patch, we choose to embed the struct device into the
watchdog_core_data, and use the API provided by the commit 233ed09
to make sure that the release of watchdog_core_data and cdev are
in sequence.

Signed-off-by: Kevin Hao <[email protected]>
Reviewed-by: Guenter Roeck <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Guenter Roeck <[email protected]>
Signed-off-by: Wim Van Sebroeck <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
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@haokexin @gregkh
haokexin authored and gregkh committed Jan 1, 2020
1 parent 6e70402 commit 5f488fa
Showing 1 changed file with 32 additions and 38 deletions.
70 changes: 32 additions & 38 deletions drivers/watchdog/watchdog_dev.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -38,7 +38,6 @@
#include <linux/init.h> /* For __init/__exit/... */
#include <linux/hrtimer.h> /* For hrtimers */
#include <linux/kernel.h> /* For printk/panic/... */
#include <linux/kref.h> /* For data references */
#include <linux/kthread.h> /* For kthread_work */
#include <linux/miscdevice.h> /* For handling misc devices */
#include <linux/module.h> /* For module stuff/... */
Expand All @@ -56,14 +55,14 @@

/*
* struct watchdog_core_data - watchdog core internal data
* @kref: Reference count.
* @dev: The watchdog's internal device
* @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 device dev;
struct cdev cdev;
struct watchdog_device *wdd;
struct mutex lock;
Expand Down Expand Up @@ -822,7 +821,7 @@ static int watchdog_open(struct inode *inode, struct file *file)
file->private_data = wd_data;

if (!hw_running)
kref_get(&wd_data->kref);
get_device(&wd_data->dev);

/* dev/watchdog is a virtual (and thus non-seekable) filesystem */
return nonseekable_open(inode, file);
Expand All @@ -834,11 +833,11 @@ static int watchdog_open(struct inode *inode, struct file *file)
return err;
}

static void watchdog_core_data_release(struct kref *kref)
static void watchdog_core_data_release(struct device *dev)
{
struct watchdog_core_data *wd_data;

wd_data = container_of(kref, struct watchdog_core_data, kref);
wd_data = container_of(dev, struct watchdog_core_data, dev);

kfree(wd_data);
}
Expand Down Expand Up @@ -898,7 +897,7 @@ static int watchdog_release(struct inode *inode, struct file *file)
*/
if (!running) {
module_put(wd_data->cdev.owner);
kref_put(&wd_data->kref, watchdog_core_data_release);
put_device(&wd_data->dev);
}
return 0;
}
Expand All @@ -917,25 +916,29 @@ static struct miscdevice watchdog_miscdev = {
.fops = &watchdog_fops,
};

static struct class watchdog_class = {
.name = "watchdog",
.owner = THIS_MODULE,
.dev_groups = wdt_groups,
};

/*
* 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)
static int watchdog_cdev_register(struct watchdog_device *wdd)
{
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;
Expand Down Expand Up @@ -964,23 +967,33 @@ static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno)
}
}

device_initialize(&wd_data->dev);
wd_data->dev.devt = MKDEV(MAJOR(watchdog_devt), wdd->id);
wd_data->dev.class = &watchdog_class;
wd_data->dev.parent = wdd->parent;
wd_data->dev.groups = wdd->groups;
wd_data->dev.release = watchdog_core_data_release;
dev_set_drvdata(&wd_data->dev, wdd);
dev_set_name(&wd_data->dev, "watchdog%d", wdd->id);

/* 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);
err = cdev_device_add(&wd_data->cdev, &wd_data->dev);
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);
put_device(&wd_data->dev);
}
return err;
}

wd_data->cdev.owner = wdd->ops->owner;

/* Record time of most recent heartbeat as 'just before now'. */
wd_data->last_hw_keepalive = ktime_sub(ktime_get(), 1);

Expand All @@ -990,7 +1003,7 @@ static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno)
*/
if (watchdog_hw_running(wdd)) {
__module_get(wdd->ops->owner);
kref_get(&wd_data->kref);
get_device(&wd_data->dev);
if (handle_boot_enabled)
hrtimer_start(&wd_data->timer, 0, HRTIMER_MODE_REL);
else
Expand All @@ -1013,7 +1026,7 @@ static void watchdog_cdev_unregister(struct watchdog_device *wdd)
{
struct watchdog_core_data *wd_data = wdd->wd_data;

cdev_del(&wd_data->cdev);
cdev_device_del(&wd_data->cdev, &wd_data->dev);
if (wdd->id == 0) {
misc_deregister(&watchdog_miscdev);
old_wd_data = NULL;
Expand All @@ -1032,15 +1045,9 @@ static void watchdog_cdev_unregister(struct watchdog_device *wdd)
hrtimer_cancel(&wd_data->timer);
kthread_cancel_work_sync(&wd_data->work);

kref_put(&wd_data->kref, watchdog_core_data_release);
put_device(&wd_data->dev);
}

static struct class watchdog_class = {
.name = "watchdog",
.owner = THIS_MODULE,
.dev_groups = wdt_groups,
};

static int watchdog_reboot_notifier(struct notifier_block *nb,
unsigned long code, void *data)
{
Expand Down Expand Up @@ -1071,35 +1078,23 @@ static int watchdog_reboot_notifier(struct notifier_block *nb,

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);
ret = watchdog_cdev_register(wdd);
if (ret)
return ret;

dev = device_create_with_groups(&watchdog_class, wdd->parent,
devno, wdd, wdd->groups,
"watchdog%d", wdd->id);
if (IS_ERR(dev)) {
watchdog_cdev_unregister(wdd);
return PTR_ERR(dev);
}

ret = watchdog_register_pretimeout(wdd);
if (ret) {
device_destroy(&watchdog_class, devno);
watchdog_cdev_unregister(wdd);
return ret;
}

if (test_bit(WDOG_STOP_ON_REBOOT, &wdd->status)) {
wdd->reboot_nb.notifier_call = watchdog_reboot_notifier;

ret = devm_register_reboot_notifier(dev, &wdd->reboot_nb);
ret = devm_register_reboot_notifier(&wdd->wd_data->dev,
&wdd->reboot_nb);
if (ret) {
pr_err("watchdog%d: Cannot register reboot notifier (%d)\n",
wdd->id, ret);
Expand All @@ -1121,7 +1116,6 @@ int watchdog_dev_register(struct watchdog_device *wdd)
void watchdog_dev_unregister(struct watchdog_device *wdd)
{
watchdog_unregister_pretimeout(wdd);
device_destroy(&watchdog_class, wdd->wd_data->cdev.dev);
watchdog_cdev_unregister(wdd);
}

Expand Down

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