linux-kernel - Re: [kernel PATCH v1 1/1] Bluetooth: Fix get clock info

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Message-ID: <CABBYNZ+ao6r4ZHaVNGRe-Wp6077R2xmkYufOK7tN=B8rEJL1yg@mail.gmail.com>
Date:   Thu, 21 Jul 2022 15:20:40 -0700
From:   Luiz Augusto von Dentz <luiz.dentz@...il.com>
To:     Zhengping Jiang <jiangzp@...gle.com>
Cc:     "linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>,
        Marcel Holtmann <marcel@...tmann.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>
Subject: Re: [kernel PATCH v1 1/1] Bluetooth: Fix get clock info

Hi Zhengping,

On Wed, Jul 20, 2022 at 4:36 PM Zhengping Jiang <jiangzp@...gle.com> wrote:
>
> If connection exists, set the connection data before calling
> get_clock_info_sync, so it can be verified the connection is still
> connected, before retrieving clock info.
>
> Signed-off-by: Zhengping Jiang <jiangzp@...gle.com>
> ---
>
> Changes in v1:
> - Fix input connection data
>
>  net/bluetooth/mgmt.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/net/bluetooth/mgmt.c b/net/bluetooth/mgmt.c
> index ef8371975c4eb..947d700574c54 100644
> --- a/net/bluetooth/mgmt.c
> +++ b/net/bluetooth/mgmt.c
> @@ -6971,11 +6971,16 @@ static int get_clock_info(struct sock *sk, struct hci_dev *hdev, void *data,
>         }
>
>         cmd = mgmt_pending_new(sk, MGMT_OP_GET_CLOCK_INFO, hdev, data, len);
> -       if (!cmd)
> +       if (!cmd) {
>                 err = -ENOMEM;
> -       else
> +       } else {
> +               if (conn) {
> +                       hci_conn_hold(conn);
> +                       cmd->user_data = hci_conn_get(conn);
> +               }
>                 err = hci_cmd_sync_queue(hdev, get_clock_info_sync, cmd,
>                                          get_clock_info_complete);
> +       }

Having seconds though if this is actually the right thing to do,
hci_cmd_sync_queue will queue the command so get_clock_info_sync
shouldn't execute immediately if that happens that actually would be
quite a problem since we are holding the hci_dev_lock so if the
callback executes and blocks waiting a command that would likely cause
a deadlock because no command can be completed while hci_dev_lock is
being held, in fact I don't really like the idea of holding hci_conn
reference either since we are doing a lookup by address on
get_clock_info_sync Id probably just remove this code as it seem
unnecessary.

Btw, there are tests for this command in mgmt-tester so if this is
actually attempting to fix a problem Id like to have a test to
reproduce it.

>         if (err < 0) {
>                 err = mgmt_cmd_complete(sk, hdev->id, MGMT_OP_GET_CLOCK_INFO,
> @@ -6984,12 +6989,8 @@ static int get_clock_info(struct sock *sk, struct hci_dev *hdev, void *data,
>                 if (cmd)
>                         mgmt_pending_free(cmd);
>
> -       } else if (conn) {
> -               hci_conn_hold(conn);
> -               cmd->user_data = hci_conn_get(conn);
>         }
>
> -
>  unlock:
>         hci_dev_unlock(hdev);
>         return err;
> --
> 2.37.0.170.g444d1eabd0-goog
>


-- 
Luiz Augusto von Dentz