Re: net/bluetooth: workqueue destruction WARNING in hci_unregister_dev

From: Jiri Slaby
Date: Tue Mar 22 2016 - 04:10:10 EST

On 03/21/2016, 04:58 PM, Jiri Slaby wrote:
> Hello,
> On 03/18/2016, 09:52 PM, Tejun Heo wrote:
>> On Thu, Mar 17, 2016 at 01:00:13PM +0100, Jiri Slaby wrote:
>>>>> I have not done that yet, but today, I see:
>>>>> destroy_workqueue: name='req_hci0' pwq=ffff88002f590300
>>>>> wq->dfl_pwq=ffff88002f591e00 pwq->refcnt=2 pwq->nr_active=0 delayed_works:
>>>>> pwq 12: cpus=0-1 node=0 flags=0x4 nice=-20 active=0/1
>>>>> in-flight: 18568:wq_barrier_func
>>>> So, this means that there's flush_work() racing against workqueue
>>>> destruction, which can't be safe. :(
>>> But I cannot trigger the WARN_ONs in the attached patch, so I am
>>> confused how this can happen :(. (While I am still seeing the destroy
>>> WARNINGs.)
>> So, no operations should be in progress when destroy_workqueue() is
>> called. If somebody was flushing a work item, the flush call must
>> have returned before destroy_workqueue() was invoked, which doesn't
>> seem to be the case here. Can you trigger BUG_ON() or sysrq-t when
>> the above triggers? There must be a task which is flushing a work
>> item there and it shouldn't be difficult to pinpoint what's going on
>> from it.
> The output of sysrq-t is here (> 200k), but I cannot see anything
> suspicious in it:

Hmm, so I seem I cannot reproduce with this hunk:
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -3139,10 +3139,10 @@ void hci_unregister_dev(struct hci_dev *hdev)

- hci_dev_do_close(hdev);

+ hci_dev_do_close(hdev);
if (!test_bit(HCI_INIT, &hdev->flags) &&
!hci_dev_test_flag(hdev, HCI_SETUP) &&
!hci_dev_test_flag(hdev, HCI_CONFIG)) {

I cannot explain why though. I do not see how it matters in this
particular case...

Dmitry, could you apply it too? But I don't know how often you see the

PS. next on the table is the gsm tty warning.

suse labs