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References: <20230502145737.140856-1-lrh2000@pku.edu.cn> <20230502145737.140856-7-lrh2000@pku.edu.cn>
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From:   Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Date:   Tue, 2 May 2023 09:18:02 -0700
Message-ID: <CABBYNZJS3QLbCPizwaTaKmy13+34vNLFo2YMy2cMS3zwvVeZsw@mail.gmail.com>
Subject: Re: [PATCH v3 6/6] Bluetooth: Avoid recursion in hci_conn_unlink
To:     Ruihan Li <lrh2000@pku.edu.cn>
Cc:     linux-bluetooth@vger.kernel.org,
        Marcel Holtmann <marcel@holtmann.org>,
        Johan Hedberg <johan.hedberg@gmail.com>
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Hi Ruihan,

On Tue, May 2, 2023 at 7:57=E2=80=AFAM Ruihan Li <lrh2000@pku.edu.cn> wrote=
:
>
> Previously, hci_conn_unlink was implemented as a recursion function. To
> unlink physical connections (e.g. ACL/LE), it calls itself to unlink all
> its logical channels (e.g. SCO/eSCO/ISO).
>
> Recursion is not required. This patch refactors hci_conn_unlink into two
> functions, where hci_conn_unlink_parent takes a physical connection,
> checks out all its logical channels, and calls hci_conn_unlink_child for
> each logical channel to unlink it.
>
> Signed-off-by: Ruihan Li <lrh2000@pku.edu.cn>
> ---
>  net/bluetooth/hci_conn.c | 55 +++++++++++++++++++++++-----------------
>  1 file changed, 32 insertions(+), 23 deletions(-)
>
> diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
> index de553e062..243d68a64 100644
> --- a/net/bluetooth/hci_conn.c
> +++ b/net/bluetooth/hci_conn.c
> @@ -1074,34 +1074,13 @@ struct hci_conn *hci_conn_add(struct hci_dev *hde=
v, int type, bdaddr_t *dst,
>         return conn;
>  }
>
> -static void hci_conn_unlink(struct hci_conn *conn)
> +static void hci_conn_unlink_parent(struct hci_conn *conn)
>  {
>         struct hci_dev *hdev =3D conn->hdev;
>
>         bt_dev_dbg(hdev, "hcon %p", conn);
>
> -       if (!conn->parent) {
> -               struct hci_link *link, *t;
> -
> -               list_for_each_entry_safe(link, t, &conn->link_list, list)=
 {
> -                       struct hci_conn *child =3D link->conn;
> -
> -                       hci_conn_unlink(child);
> -
> -                       /* Due to race, SCO connection might be not estab=
lished
> -                        * yet at this point. Delete it now, otherwise it=
 is
> -                        * possible for it to be stuck and can't be delet=
ed.
> -                        */
> -                       if ((child->type =3D=3D SCO_LINK ||
> -                            child->type =3D=3D ESCO_LINK) &&
> -                           child->handle =3D=3D HCI_CONN_HANDLE_UNSET)
> -                               hci_conn_del(child);
> -               }
> -
> -               return;
> -       }
> -
> -       if (!conn->link)
> +       if (WARN_ON(!conn->link))
>                 return;
>
>         list_del_rcu(&conn->link->list);
> @@ -1115,6 +1094,36 @@ static void hci_conn_unlink(struct hci_conn *conn)
>         conn->link =3D NULL;
>  }
>
> +static void hci_conn_unlink_children(struct hci_conn *conn)
> +{
> +       struct hci_dev *hdev =3D conn->hdev;
> +       struct hci_link *link, *t;
> +
> +       bt_dev_dbg(hdev, "hcon %p", conn);
> +
> +       list_for_each_entry_safe(link, t, &conn->link_list, list) {
> +               struct hci_conn *child =3D link->conn;
> +
> +               hci_conn_unlink_parent(child);
> +
> +               /* Due to race, SCO connection might be not established
> +                * yet at this point. Delete it now, otherwise it is
> +                * possible for it to be stuck and can't be deleted.
> +                */
> +               if (child->type =3D=3D SCO_LINK || child->type =3D=3D ESC=
O_LINK)
> +                       if (child->handle =3D=3D HCI_CONN_HANDLE_UNSET)
> +                               hci_conn_del(child);
> +       }

This is not quite right, when we are unlinking the children's hci_conn
it shall only unlink itself from the parent not everything.

> +}
> +
> +static void hci_conn_unlink(struct hci_conn *conn)
> +{
> +       if (conn->parent)
> +               hci_conn_unlink_parent(conn);
> +       else
> +               hci_conn_unlink_children(conn);
> +}
> +
>  void hci_conn_del(struct hci_conn *conn)
>  {
>         struct hci_dev *hdev =3D conn->hdev;
> --
> 2.40.0
>


--=20
Luiz Augusto von Dentz