netdev - 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 20:38:48 +0200
From:   Mateusz Jończyk <mat.jonczyk@...pl>
To:     Vasyl Vavrychuk <vasyl.vavrychuk@...nsynergy.com>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-bluetooth@...r.kernel.org,
        Max Krummenacher <max.oss.09@...il.com>,
        Francesco Dolcini <francesco.dolcini@...adex.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Marcel Holtmann <marcel@...tmann.org>,
        max.krummenacher@...adex.com
Cc:     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.

W dniu 5.07.2022 o 14:59, Vasyl Vavrychuk pisze:
> `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>

Works well: suspend (with bluetooth on and also off), hibernation, sending files, rfkill.

Thank you.

Reported-and-tested-by: Mateusz Jończyk <mat.jonczyk@...pl>

Greetings,

Mateusz Jończyk