Re: net/bluetooth: workqueue destruction WARNING in hci_unregister_dev

[Dmitry Vyukov]

On Tue, Jan 26, 2016 at 12:53 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> Hello,
>
> I've hit the following warning while running syzkaller fuzzer:
>
> ------------[ cut here ]------------
> WARNING: CPU: 2 PID: 17409 at kernel/workqueue.c:3968
> destroy_workqueue+0x172/0x550()
> Modules linked in:
> CPU: 2 PID: 17409 Comm: syz-executor Not tainted 4.5.0-rc1+ #283
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>  00000000ffffffff ffff88003665f8a0 ffffffff8299a06d 0000000000000000
>  ffff88003599c740 ffffffff8643f0c0 ffff88003665f8e0 ffffffff8134fcf9
>  ffffffff8139d4c2 ffffffff8643f0c0 0000000000000f80 ffff8800630c5ae8
> Call Trace:
>  [<     inline     >] __dump_stack lib/dump_stack.c:15
>  [<ffffffff8299a06d>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50
>  [<ffffffff8134fcf9>] warn_slowpath_common+0xd9/0x140 kernel/panic.c:482
>  [<ffffffff8134ff29>] warn_slowpath_null+0x29/0x30 kernel/panic.c:515
>  [<ffffffff8139d4c2>] destroy_workqueue+0x172/0x550 kernel/workqueue.c:3968
>  [<ffffffff85a714a4>] hci_unregister_dev+0x264/0x700
> net/bluetooth/hci_core.c:3162
>  [<ffffffff84595ce6>] vhci_release+0x76/0xe0 drivers/bluetooth/hci_vhci.c:341
>  [<ffffffff817b2376>] __fput+0x236/0x780 fs/file_table.c:208
>  [<ffffffff817b2945>] ____fput+0x15/0x20 fs/file_table.c:244
>  [<ffffffff813ad760>] task_work_run+0x170/0x210 kernel/task_work.c:115
>  [<     inline     >] exit_task_work include/linux/task_work.h:21
>  [<ffffffff81358da5>] do_exit+0x8b5/0x2c60 kernel/exit.c:748
>  [<ffffffff8135b2c8>] do_group_exit+0x108/0x330 kernel/exit.c:878
>  [<ffffffff8137e434>] get_signal+0x5e4/0x14f0 kernel/signal.c:2307
>  [<ffffffff811a1db3>] do_signal+0x83/0x1c90 arch/x86/kernel/signal.c:712
>  [<ffffffff81006685>] exit_to_usermode_loop+0x1a5/0x210
> arch/x86/entry/common.c:247
>  [<     inline     >] prepare_exit_to_usermode arch/x86/entry/common.c:282
>  [<ffffffff810084ea>] syscall_return_slowpath+0x2ba/0x340
> arch/x86/entry/common.c:344
>  [<ffffffff863597a2>] int_ret_from_sys_call+0x25/0x9f
> arch/x86/entry/entry_64.S:281
> ---[ end trace f627386faee7426f ]---
>
> Unfortunately I cannot reproduce it in a controlled environment, but
> I've hit it twice in different VMs. So maybe if you see something
> obvious there. Is it possible that something is submitted into the
> workqueue between it is drained and destroyed in hci_unregister_dev?
>
> On commit 92e963f50fc74041b5e9e744c330dca48e04f08d (Jan 24).


Wait, I was able to reproduce it by running the following program in a
parallel loop for several hours:
https://gist.githubusercontent.com/dvyukov/c15675af95e599fe6631/raw/c34117b54d0352f5df4f572d4151a94557780a9b/gistfile1.txt
I think that you just need to open /dev/vhci, because the program does
not seem to do anything useful with the descriptor.
Machine died, full log is here:
https://gist.githubusercontent.com/dvyukov/4584d70c2b4bee7ca875/raw/3794fb9f4c8e0fb2f91261a66725b042b5de4e0f/gistfile1.txt