linux-kernel - Re: [PATCH] Bluetooth: core: Fix deadlock due to `cancel_work_sync(&hdev->power_on)` from hci_power_on

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Date:   Tue, 5 Jul 2022 16:12:41 +0200
From:   Max Krummenacher <max.oss.09@...il.com>
To:     Vasyl Vavrychuk <vasyl.vavrychuk@...nsynergy.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        netdev@...r.kernel.org, linux-bluetooth@...r.kernel.org,
        Francesco Dolcini <francesco.dolcini@...adex.com>,
        Mateusz Jończyk <mat.jonczyk@...pl>,
        Jakub Kicinski <kuba@...nel.org>,
        Marcel Holtmann <marcel@...tmann.org>,
        Max Krummenacher <max.krummenacher@...adex.com>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH] Bluetooth: core: Fix deadlock due to `cancel_work_sync(&hdev->power_on)`
 from hci_power_on_sync.

On Tue, Jul 5, 2022 at 3:00 PM Vasyl Vavrychuk
<vasyl.vavrychuk@...nsynergy.com> wrote:
>
> `cancel_work_sync(&hdev->power_on)` was moved to hci_dev_close_sync in
> commit [1] to ensure that power_on work is canceled after HCI interface
> down.
>
> But, in certain cases power_on work function may call hci_dev_close_sync
> itself: hci_power_on -> hci_dev_do_close -> hci_dev_close_sync ->
> cancel_work_sync(&hdev->power_on), causing deadlock. In particular, this
> happens when device is rfkilled on boot. To avoid deadlock, move
> power_on work canceling out of hci_dev_do_close/hci_dev_close_sync.
>
> Deadlock introduced by commit [1] was reported in [2,3] as broken
> suspend. Suspend did not work because `hdev->req_lock` held as result of
> `power_on` work deadlock. In fact, other BT features were not working.
> It was not observed when testing [1] since it was verified without
> rfkill in place.
>
> NOTE: It is not needed to cancel power_on work from other places where
> hci_dev_do_close/hci_dev_close_sync is called in case:
> * Requests were serialized due to `hdev->req_workqueue`. The power_on
> work is first in that workqueue.
> * hci_rfkill_set_block which won't close device anyway until HCI_SETUP
> is on.
> * hci_sock_release which runs after hci_sock_bind which ensures
> HCI_SETUP was cleared.
>
> As result, behaviour is the same as in pre-dd06ed7 commit, except
> power_on work cancel added to hci_dev_close.
>
> [1]: commit dd06ed7ad057 ("Bluetooth: core: Fix missing power_on work cancel on HCI close")
> [2]: https://lore.kernel.org/lkml/20220614181706.26513-1-max.oss.09@gmail.com/
> [2]: https://lore.kernel.org/lkml/1236061d-95dd-c3ad-a38f-2dae7aae51ef@o2.pl/
>
> Fixes: commit dd06ed7ad057 ("Bluetooth: core: Fix missing power_on work cancel on HCI close")
> Signed-off-by: Vasyl Vavrychuk <vasyl.vavrychuk@...nsynergy.com>
> Reported-by: Max Krummenacher <max.krummenacher@...adex.com>
> Reported-by: Mateusz Jonczyk <mat.jonczyk@...pl>
> ---
>  net/bluetooth/hci_core.c | 3 +++
>  net/bluetooth/hci_sync.c | 1 -
>  2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
> index 59a5c1341c26..a0f99baafd35 100644
> --- a/net/bluetooth/hci_core.c
> +++ b/net/bluetooth/hci_core.c
> @@ -571,6 +571,7 @@ int hci_dev_close(__u16 dev)
>                 goto done;
>         }
>
> +       cancel_work_sync(&hdev->power_on);
>         if (hci_dev_test_and_clear_flag(hdev, HCI_AUTO_OFF))
>                 cancel_delayed_work(&hdev->power_off);
>
> @@ -2675,6 +2676,8 @@ void hci_unregister_dev(struct hci_dev *hdev)
>         list_del(&hdev->list);
>         write_unlock(&hci_dev_list_lock);
>
> +       cancel_work_sync(&hdev->power_on);
> +
>         hci_cmd_sync_clear(hdev);
>
>         if (!test_bit(HCI_QUIRK_NO_SUSPEND_NOTIFIER, &hdev->quirks))
> diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
> index 286d6767f017..1739e8cb3291 100644
> --- a/net/bluetooth/hci_sync.c
> +++ b/net/bluetooth/hci_sync.c
> @@ -4088,7 +4088,6 @@ int hci_dev_close_sync(struct hci_dev *hdev)
>
>         bt_dev_dbg(hdev, "");
>
> -       cancel_work_sync(&hdev->power_on);
>         cancel_delayed_work(&hdev->power_off);
>         cancel_delayed_work(&hdev->ncmd_timer);
>
> --
> 2.30.2
>

This fixes the issue I described in [1]. I.e. The kernel no longer
freezes while going to suspend.
Tested-by: Max Krummenacher <max.krummenacher@...adex.com>

Thanks!
Max