Re: [PATCH v2] Bluetooth: When HCI work queue is drained, only queue chained work

[Luiz Augusto von Dentz]

Hi Schspa,

On Thu, Jun 2, 2022 at 12:20 PM Schspa Shi <schspa@xxxxxxxxx> wrote:
>
> The HCI command, event, and data packet processing workqueue is drained
> to avoid deadlock in commit
> 76727c02c1e1 ("Bluetooth: Call drain_workqueue() before resetting state").
>
> There is another delayed work, which will queue command to this drained
> workqueue. Which results in the following error report:
>
> Bluetooth: hci2: command 0x040f tx timeout
> WARNING: CPU: 1 PID: 18374 at kernel/workqueue.c:1438 __queue_work+0xdad/0x1140
> Workqueue: events hci_cmd_timeout
> RIP: 0010:__queue_work+0xdad/0x1140
> RSP: 0000:ffffc90002cffc60 EFLAGS: 00010093
> RAX: 0000000000000000 RBX: ffff8880b9d3ec00 RCX: 0000000000000000
> RDX: ffff888024ba0000 RSI: ffffffff814e048d RDI: ffff8880b9d3ec08
> RBP: 0000000000000008 R08: 0000000000000000 R09: 00000000b9d39700
> R10: ffffffff814f73c6 R11: 0000000000000000 R12: ffff88807cce4c60
> R13: 0000000000000000 R14: ffff8880796d8800 R15: ffff8880796d8800
> FS:  0000000000000000(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000c0174b4000 CR3: 000000007cae9000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  ? queue_work_on+0xcb/0x110
>  ? lockdep_hardirqs_off+0x90/0xd0
>  queue_work_on+0xee/0x110
>  process_one_work+0x996/0x1610
>  ? pwq_dec_nr_in_flight+0x2a0/0x2a0
>  ? rwlock_bug.part.0+0x90/0x90
>  ? _raw_spin_lock_irq+0x41/0x50
>  worker_thread+0x665/0x1080
>  ? process_one_work+0x1610/0x1610
>  kthread+0x2e9/0x3a0
>  ? kthread_complete_and_exit+0x40/0x40
>  ret_from_fork+0x1f/0x30
>  </TASK>
>
> To fix this, we can add a new HCI_DRAIN_WQ flag, and don't queue the
> timeout workqueue while command workqueue is draining.
>
> Fixes: 76727c02c1e1 ("Bluetooth: Call drain_workqueue() before resetting state")
> Reported-by: syzbot+63bed493aebbf6872647@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Schspa Shi <schspa@xxxxxxxxx>
>
> Changelog:
> v1 -> v2:
>         - Move the workqueue drain flag to controller flags, and use hci_dev_*_flag.
>         - Add missing ncmd_timer cancel.
>         - Clear DRAIN_WORKQUEUE flag after device command flushed.
> ---
>  include/net/bluetooth/hci.h |  1 +
>  net/bluetooth/hci_core.c    | 10 +++++++++-
>  net/bluetooth/hci_event.c   |  5 +++--
>  3 files changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
> index fe7935be7dc4..4a45c48eb0d2 100644
> --- a/include/net/bluetooth/hci.h
> +++ b/include/net/bluetooth/hci.h
> @@ -361,6 +361,7 @@ enum {
>         HCI_QUALITY_REPORT,
>         HCI_OFFLOAD_CODECS_ENABLED,
>         HCI_LE_SIMULTANEOUS_ROLES,
> +       HCI_CMD_DRAIN_WORKQUEUE,
>
>         __HCI_NUM_FLAGS,
>  };
> diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
> index 5abb2ca5b129..e908fdc4625c 100644
> --- a/net/bluetooth/hci_core.c
> +++ b/net/bluetooth/hci_core.c
> @@ -593,6 +593,11 @@ static int hci_dev_do_reset(struct hci_dev *hdev)
>         skb_queue_purge(&hdev->rx_q);
>         skb_queue_purge(&hdev->cmd_q);
>
> +       /* Cancel these not cahined pending work */
> +       hci_dev_set_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE);

There seems to be a typo on the comment line 'cahined', also perhaps
you test it before setting it so we don't risk flushing multiple
times?

> +       cancel_delayed_work(&hdev->cmd_timer);
> +       cancel_delayed_work(&hdev->ncmd_timer);
> +
>         /* Avoid potential lockdep warnings from the *_flush() calls by
>          * ensuring the workqueue is empty up front.
>          */
> @@ -606,6 +611,8 @@ static int hci_dev_do_reset(struct hci_dev *hdev)
>         if (hdev->flush)
>                 hdev->flush(hdev);
>
> +       hci_dev_clear_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE);
> +
>         atomic_set(&hdev->cmd_cnt, 1);
>         hdev->acl_cnt = 0; hdev->sco_cnt = 0; hdev->le_cnt = 0;
>
> @@ -3861,7 +3868,8 @@ static void hci_cmd_work(struct work_struct *work)
>                         if (res < 0)
>                                 __hci_cmd_sync_cancel(hdev, -res);
>
> -                       if (test_bit(HCI_RESET, &hdev->flags))
> +                       if (test_bit(HCI_RESET, &hdev->flags) ||
> +                           hci_dev_test_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE))
>                                 cancel_delayed_work(&hdev->cmd_timer);
>                         else
>                                 schedule_delayed_work(&hdev->cmd_timer,
> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> index af17dfb20e01..7cb956d3abb2 100644
> --- a/net/bluetooth/hci_event.c
> +++ b/net/bluetooth/hci_event.c
> @@ -3768,8 +3768,9 @@ static inline void handle_cmd_cnt_and_timer(struct hci_dev *hdev, u8 ncmd)
>                         cancel_delayed_work(&hdev->ncmd_timer);
>                         atomic_set(&hdev->cmd_cnt, 1);
>                 } else {
> -                       schedule_delayed_work(&hdev->ncmd_timer,
> -                                             HCI_NCMD_TIMEOUT);
> +                       if (!hci_dev_test_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE))
> +                               schedule_delayed_work(&hdev->ncmd_timer,
> +                                                     HCI_NCMD_TIMEOUT);
>                 }
>         }
>  }
> --
> 2.24.3 (Apple Git-128)
>


-- 
Luiz Augusto von Dentz