[PATCH AUTOSEL 5.5 086/121] i2c: dev: Fix the race between the release of i2c_dev and cdev

Sasha Levin
2020-04-11T23:35:56Z

From: Kevin Hao <haokexin@gmail.com>

[ Upstream commit 1413ef638abae4ab5621901cf4d8ef08a4a48ba6 ]

The struct cdev is embedded in the struct i2c_dev. In the current code,
we would free the i2c_dev struct directly in put_i2c_dev(), but the
cdev is manged by a kobject, and the release of it is not predictable.
So it is very possible that the i2c_dev 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: 19 PID: 1 at lib/debugobjects.c:325 debug_print_object+0xb0/0xf0
Modules linked in:
CPU: 19 PID: 1 Comm: swapper/0 Tainted: G W 5.2.20-yocto-standard+ #120
Hardware name: Marvell OcteonTX CN96XX board (DT)
pstate: 80c00089 (Nzcv daIf +PAN +UAO)
pc : debug_print_object+0xb0/0xf0
lr : debug_print_object+0xb0/0xf0
sp : ffff00001292f7d0
x29: ffff00001292f7d0 x28: ffff800b82151788
x27: 0000000000000001 x26: ffff800b892c0000
x25: ffff0000124a2558 x24: 0000000000000000
x23: ffff00001107a1d8 x22: ffff0000116b5088
x21: ffff800bdc6afca8 x20: ffff000012471ae8
x19: ffff00001168f2c8 x18: 0000000000000010
x17: 00000000fd6f304b x16: 00000000ee79de43
x15: ffff800bc0e80568 x14: 79616c6564203a74
x13: 6e6968207473696c x12: 5f72656d6974203a
x11: ffff0000113f0018 x10: 0000000000000000
x9 : 000000000000001f x8 : 0000000000000000
x7 : ffff0000101294cc x6 : 0000000000000000
x5 : 0000000000000000 x4 : 0000000000000001
x3 : 00000000ffffffff x2 : 0000000000000000
x1 : 387fc15c8ec0f200 x0 : 0000000000000000
Call trace:
debug_print_object+0xb0/0xf0
__debug_check_no_obj_freed+0x19c/0x228
debug_check_no_obj_freed+0x1c/0x28
kfree+0x250/0x440
put_i2c_dev+0x68/0x78
i2cdev_detach_adapter+0x60/0xc8
i2cdev_notifier_call+0x3c/0x70
notifier_call_chain+0x8c/0xe8
blocking_notifier_call_chain+0x64/0x88
device_del+0x74/0x380
device_unregister+0x54/0x78
i2c_del_adapter+0x278/0x2d0
unittest_i2c_bus_remove+0x3c/0x80
platform_drv_remove+0x30/0x50
device_release_driver_internal+0xf4/0x1c0
driver_detach+0x58/0xa0
bus_remove_driver+0x84/0xd8
driver_unregister+0x34/0x60
platform_driver_unregister+0x20/0x30
of_unittest_overlay+0x8d4/0xbe0
of_unittest+0xae8/0xb3c
do_one_initcall+0xac/0x450
do_initcall_level+0x208/0x224
kernel_init_freeable+0x2d8/0x36c
kernel_init+0x18/0x108
ret_from_fork+0x10/0x1c
irq event stamp: 3934661
hardirqs last enabled at (3934661): [<ffff00001009fa04>] debug_exception_exit+0x4c/0x58
hardirqs last disabled at (3934660): [<ffff00001009fb14>] debug_exception_enter+0xa4/0xe0
softirqs last enabled at (3934654): [<ffff000010081d94>] __do_softirq+0x46c/0x628
softirqs last disabled at (3934649): [<ffff0000100b4a1c>] irq_exit+0x104/0x118

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 i2c_dev,
and use the API provided by the commit 233ed09d7fda to make sure that
the release of i2c_dev and cdev are in sequence.

Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/i2c/i2c-dev.c | 48 +++++++++++++++++++++++--------------------
1 file changed, 26 insertions(+), 22 deletions(-)

diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c
index 2ea4585d18c5e..94beacc41302f 100644
--- a/drivers/i2c/i2c-dev.c
+++ b/drivers/i2c/i2c-dev.c
@@ -40,7 +40,7 @@
struct i2c_dev {
struct list_head list;
struct i2c_adapter *adap;
- struct device *dev;
+ struct device dev;
struct cdev cdev;
};

@@ -84,12 +84,14 @@ static struct i2c_dev *get_free_i2c_dev(struct i2c_adapter *adap)
return i2c_dev;
}

-static void put_i2c_dev(struct i2c_dev *i2c_dev)
+static void put_i2c_dev(struct i2c_dev *i2c_dev, bool del_cdev)
{
spin_lock(&i2c_dev_list_lock);
list_del(&i2c_dev->list);
spin_unlock(&i2c_dev_list_lock);
- kfree(i2c_dev);
+ if (del_cdev)
+ cdev_device_del(&i2c_dev->cdev, &i2c_dev->dev);
+ put_device(&i2c_dev->dev);
}

static ssize_t name_show(struct device *dev,
@@ -628,6 +630,14 @@ static const struct file_operations i2cdev_fops = {

static struct class *i2c_dev_class;

+static void i2cdev_dev_release(struct device *dev)
+{
+ struct i2c_dev *i2c_dev;
+
+ i2c_dev = container_of(dev, struct i2c_dev, dev);
+ kfree(i2c_dev);
+}
+
static int i2cdev_attach_adapter(struct device *dev, void *dummy)
{
struct i2c_adapter *adap;
@@ -644,27 +654,23 @@ static int i2cdev_attach_adapter(struct device *dev, void *dummy)

cdev_init(&i2c_dev->cdev, &i2cdev_fops);
i2c_dev->cdev.owner = THIS_MODULE;
- res = cdev_add(&i2c_dev->cdev, MKDEV(I2C_MAJOR, adap->nr), 1);
- if (res)
- goto error_cdev;
-
- /* register this i2c device with the driver core */
- i2c_dev->dev = device_create(i2c_dev_class, &adap->dev,
- MKDEV(I2C_MAJOR, adap->nr), NULL,
- "i2c-%d", adap->nr);
- if (IS_ERR(i2c_dev->dev)) {
- res = PTR_ERR(i2c_dev->dev);
- goto error;
+
+ device_initialize(&i2c_dev->dev);
+ i2c_dev->dev.devt = MKDEV(I2C_MAJOR, adap->nr);
+ i2c_dev->dev.class = i2c_dev_class;
+ i2c_dev->dev.parent = &adap->dev;
+ i2c_dev->dev.release = i2cdev_dev_release;
+ dev_set_name(&i2c_dev->dev, "i2c-%d", adap->nr);
+
+ res = cdev_device_add(&i2c_dev->cdev, &i2c_dev->dev);
+ if (res) {
+ put_i2c_dev(i2c_dev, false);
+ return res;
}

pr_debug("i2c-dev: adapter [%s] registered as minor %d\n",
adap->name, adap->nr);
return 0;
-error:
- cdev_del(&i2c_dev->cdev);
-error_cdev:
- put_i2c_dev(i2c_dev);
- return res;
}

static int i2cdev_detach_adapter(struct device *dev, void *dummy)
@@ -680,9 +686,7 @@ static int i2cdev_detach_adapter(struct device *dev, void *dummy)
if (!i2c_dev) /* attach_adapter must have failed */
return 0;

- cdev_del(&i2c_dev->cdev);
- put_i2c_dev(i2c_dev);
- device_destroy(i2c_dev_class, MKDEV(I2C_MAJOR, adap->nr));
+ put_i2c_dev(i2c_dev, true);

pr_debug("i2c-dev: adapter [%s] unregistered\n", adap->name);
return 0;
--
2.20.1