linux-kernel - Re: [PATCH 3/5] Bluetooth: hci_event: Remove limit of 2 reconnection attempts

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Date: Wed, 3 Jan 2024 11:05:05 -0500
From: Luiz Augusto von Dentz <luiz.dentz@...il.com>
To: Jonas Dreßler <verdre@...d.nl>
Cc: Marcel Holtmann <marcel@...tmann.org>, Johan Hedberg <johan.hedberg@...il.com>, 
	linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org, 
	netdev@...r.kernel.org
Subject: Re: [PATCH 3/5] Bluetooth: hci_event: Remove limit of 2 reconnection attempts

Hi Jonas,

On Tue, Jan 2, 2024 at 1:59 PM Jonas Dreßler <verdre@...d.nl> wrote:
>
> Since commit 4c67bc74f016b0d360b8573e18969c0ff7926974, we retry connecting
> later when we get a "Command Disallowed" error returned by "Create
> Connection".
>
> In this commit the intention was to retry only once, and give up if we see
> "Command Disallowed" again on the second try.
>
> This made sense back then when the retry was initiated *only* from the
> "Connect Complete" event. If we received that event, we knew that now the
> card now must have a "free slot" for a new connection request again. These
> days we call hci_conn_check_pending() from a few more places though, and
> in these places we can't really be sure that there's a "free slot" on the
> card, so the second try to "Create Connection" might fail again.
>
> Deal with this by being less strict about these retries and try again
> every time we get "Command Disallowed" errors, removing the limitation to
> only two attempts.
>
> Since this can potentially cause us to enter an endless cycle of
> reconnection attempts, we'll add some guarding against that with the next
> commit.

Don't see where you are doing such guarding, besides you seem to
assume HCI_ERROR_COMMAND_DISALLOWED would always means the controller
is busy, or something like that, but it could perform the connection
later, but that may not always be the case, thus why I think
reconnecting just a few number of times is better, if you really need
to keep retrying then this needs to be controlled by a policy in
userspace not hardcoded in the kernel, well I can even argument that
perhaps the initial number of reconnection shall be configurable so
one don't have to recompile the kernel if that needs changing.

> Signed-off-by: Jonas Dreßler <verdre@...d.nl>
> ---
>  net/bluetooth/hci_event.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> index e8b4a0126..e1f5b6f90 100644
> --- a/net/bluetooth/hci_event.c
> +++ b/net/bluetooth/hci_event.c
> @@ -2323,12 +2323,13 @@ static void hci_cs_create_conn(struct hci_dev *hdev, __u8 status)
>
>         if (status) {
>                 if (conn && conn->state == BT_CONNECT) {
> -                       if (status != HCI_ERROR_COMMAND_DISALLOWED || conn->attempt > 2) {
> +                       if (status == HCI_ERROR_COMMAND_DISALLOWED) {
> +                               conn->state = BT_CONNECT2;
> +                       } else {
>                                 conn->state = BT_CLOSED;
>                                 hci_connect_cfm(conn, status);
>                                 hci_conn_del(conn);
> -                       } else
> -                               conn->state = BT_CONNECT2;
> +                       }
>                 }
>         } else {
>                 if (!conn) {
> --
> 2.43.0
>


-- 
Luiz Augusto von Dentz