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

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Message-Id: <20220705125931.3601-1-vasyl.vavrychuk@opensynergy.com>
Date:   Tue,  5 Jul 2022 15:59:31 +0300
From:   Vasyl Vavrychuk <vasyl.vavrychuk@...nsynergy.com>
To:     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>,
        Mateusz Jończyk <mat.jonczyk@...pl>,
        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>,
        Vasyl Vavrychuk <vasyl.vavrychuk@...nsynergy.com>
Subject: [PATCH] Bluetooth: core: Fix deadlock due to `cancel_work_sync(&hdev->power_on)` from hci_power_on_sync.

`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