On Tue, Mar 22, 2016 at 1:32 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > On Tue, Mar 22, 2016 at 9:09 AM, Jiri Slaby <jslaby@xxxxxxx> wrote: >> 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: >>> http://www.fi.muni.cz/~xslaby/sklad/panics/jctl.txt >> >> 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) >> list_del(&hdev->list); >> write_unlock(&hci_dev_list_lock); >> >> - hci_dev_do_close(hdev); >> - >> cancel_work_sync(&hdev->power_on); >> >> + 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 >> warning. > > I've seen it only several times in several months, so I don't it will > be helpful. Bad news: I hit it again. On 0f98f121e1670eaa2a2fbb675e07d6ba7f0e146f of linux-next, so I have bf389cabb3b8079c23f9762e62b05f291e2d5e99. WARNING: CPU: 3 PID: 23168 at kernel/workqueue.c:4029 destroy_workqueue+0x172/0x620 CPU: 3 PID: 23168 Comm: syz-executor Not tainted 4.8.0-rc3-next-20160825+ #8 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 ffffffff886b6fe0 ffff880037be77a8 ffffffff82db38d9 ffffffff00000016 fffffbfff10d6dfc ffffffff8708f000 ffff880037be7880 ffffffff8709be00 dffffc0000000000 0000000000000009 ffff880037be7870 ffffffff816cf888 Call Trace: [< inline >] __dump_stack lib/dump_stack.c:15 [<ffffffff82db38d9>] dump_stack+0x12e/0x185 lib/dump_stack.c:51 [<ffffffff816cf888>] panic+0x1e4/0x3fb kernel/panic.c:179 [<ffffffff813863b4>] __warn+0x1c4/0x1e0 kernel/panic.c:542 [<ffffffff8138659c>] warn_slowpath_null+0x2c/0x40 kernel/panic.c:585 [<ffffffff813dc6d2>] destroy_workqueue+0x172/0x620 kernel/workqueue.c:4029 [<ffffffff8645973f>] hci_unregister_dev+0x3df/0x8a0 net/bluetooth/hci_core.c:3170 [<ffffffff84cb6926>] vhci_release+0x76/0xf0 drivers/bluetooth/hci_vhci.c:354 [<ffffffff81868bbc>] __fput+0x28c/0x780 fs/file_table.c:208 [<ffffffff81869135>] ____fput+0x15/0x20 fs/file_table.c:244 [<ffffffff813ebf63>] task_work_run+0xf3/0x170 [< inline >] exit_task_work include/linux/task_work.h:21 [<ffffffff81394218>] do_exit+0x868/0x2e70 kernel/exit.c:828 [<ffffffff81396998>] do_group_exit+0x108/0x330 kernel/exit.c:958 [<ffffffff813ba4aa>] get_signal+0x62a/0x15d0 kernel/signal.c:2307 [<ffffffff81202333>] do_signal+0x83/0x1f60 arch/x86/kernel/signal.c:805 [<ffffffff81006345>] exit_to_usermode_loop+0x1a5/0x210 arch/x86/entry/common.c:163 [< inline >] prepare_exit_to_usermode arch/x86/entry/common.c:198 [<ffffffff8100869f>] syscall_return_slowpath+0x2bf/0x340 arch/x86/entry/common.c:267 [<ffffffff86e1079c>] entry_SYSCALL_64_fastpath+0xbf/0xc1 -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
