linux-kernel - Re: kernel panic on device removal when using a workqueue and delayed

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Date:	Mon, 31 Oct 2011 11:26:58 +0100
From:	Frank Schäfer <fschaefer.oss@...glemail.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: kernel panic on device removal when using a workqueue and delayed_work

Am 31.10.2011 04:11, schrieb Yong Zhang:
> On Sun, Oct 30, 2011 at 08:19:10PM +0100, Frank Sch�fer wrote:
>> Hi,
>>
>> with the following simple kernel module, I have a good chance to get
>> a kernel panic when I unplug the device:
>>
>>
>> #include<linux/workqueue.h>
>> #include<linux/usb.h>
>> #include<linux/module.h>
>>
>> MODULE_AUTHOR("Nobody");
>> MODULE_DESCRIPTION("example driver for causing kernel panic");
>> MODULE_LICENSE("GPL");
>>
>> static struct delayed_work poll_work;
>>
>> static void poll(struct work_struct *work)
>> {
>>      schedule_delayed_work(&poll_work,
>>                    msecs_to_jiffies(100));
>> }
>>
>> static int test_probe(struct usb_interface *intf,
>>                const struct usb_device_id *id)
>> {
>>      INIT_DELAYED_WORK(&poll_work, poll);
>>      schedule_delayed_work(&poll_work,
>>                    msecs_to_jiffies(100));
>>      return 0;
>> }
>>
>> static void test_disconnect(struct usb_interface *intf)
>> {
>>      cancel_delayed_work_sync(&poll_work);
>> }
...
>> static const struct usb_device_id device_table[] = {
>>      {USB_DEVICE(0x1234, 0x5678)},
>>      {}
>> };
>>
>> MODULE_DEVICE_TABLE(usb, device_table);
>>
>> static struct usb_driver test_driver = {
>>      .name       = "test",
>>      .id_table   = device_table,
>>      .probe      = test_probe,
>>      .disconnect = test_disconnect,
>> };
>>
>> static int __init test_mod_init(void)
>> {
>>      return usb_register(&test_driver);
>> }
>>
>> static void __exit test_mod_exit(void)
>> {
>>      usb_deregister(&test_driver);
>> }
>>
>> module_init(test_mod_init);
>> module_exit(test_mod_exit);
>>
>>
>>
>>
>> A picture of the backtrace (the machine immediately turns off
>> without saving a backtrace) can be found at
>>
>> http://imageshack.us/photo/my-images/823/img075gv.jpg
>>
>> Kernel version is 3.1.0.
>>
>>
>> This is the first time I'm using a workqueue, so there is a good
>> chance that I missed something...
> You should cancel the work you have armed before exit.
> See cancel_delayed_work().
That's what I'm doing (see above).
Did you read the code ? ;-)

Regards,
Frank Schaefer
>> Or is this a kernel bug ?
> I don't think so.
>
> Thanks,
> Yong

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