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Subject[PATCH 5.4 085/191] watchdog: Fix the race between the release of watchdog_core_data and cdev
Date
From: Kevin Hao <haokexin@gmail.com>

[ Upstream commit 72139dfa2464e43957d330266994740bb7be2535 ]

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+ #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 233ed09d7fda ("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 233ed09d7fda
to make sure that the release of watchdog_core_data and cdev are
in sequence.

Signed-off-by: Kevin Hao <haokexin@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20191008112934.29669-1-haokexin@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/watchdog/watchdog_dev.c | 70 +++++++++++++++------------------
1 file changed, 32 insertions(+), 38 deletions(-)

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index d3acc0a7256c..62483a99105c 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -34,7 +34,6 @@
#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/... */
@@ -52,14 +51,14 @@

/*
* 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;
@@ -840,7 +839,7 @@ 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);

/*
* open_timeout only applies for the first open from
@@ -861,11 +860,11 @@ out_clear:
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);
}
@@ -925,7 +924,7 @@ done:
*/
if (!running) {
module_put(wd_data->cdev.owner);
- kref_put(&wd_data->kref, watchdog_core_data_release);
+ put_device(&wd_data->dev);
}
return 0;
}
@@ -944,17 +943,22 @@ 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;
@@ -962,7 +966,6 @@ static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno)
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;
@@ -991,23 +994,33 @@ 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);
watchdog_set_open_deadline(wd_data);
@@ -1018,7 +1031,7 @@ 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_HARD);
@@ -1042,7 +1055,7 @@ 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;
@@ -1061,15 +1074,9 @@ 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)
{
@@ -1100,27 +1107,14 @@ 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;
}
@@ -1128,7 +1122,8 @@ int watchdog_dev_register(struct watchdog_device *wdd)
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);
@@ -1150,7 +1145,6 @@ 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);
}

--
2.20.1


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