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

[Jonas Dreßler]

Hi Luiz,

On 1/5/24 17:05, Luiz Augusto von Dentz wrote:
> Hi Jonas,
>
> On Fri, Jan 5, 2024 at 10:54 AM Jonas Dreßler <verdre@xxxxxxx> wrote:
> > Hi Luiz,
> >
> > On 1/3/24 17:05, Luiz Augusto von Dentz wrote:
> > > Hi Jonas,
> > >
> > > On Tue, Jan 2, 2024 at 1:59 PM Jonas Dreßler <verdre@xxxxxxx> 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.
> >
> > Yes, fair enough, the next commit assumes that COMMAND_DISALLOWED always
> > means busy. The guarding is that we stop retrying as soon as there's no
> > (competing) ongoing connection attempt nor an active inquiry, which
> > should eventually be the case no matter what, no?
> >
> > I agree it's probably still better to not rely on this fairly complex
> > sanity check and keep the checking of attempts nonetheless.
> >
> > I think we could keep doing that if we check for
> > !hci_conn_hash_lookup_state(hdev, ACL_LINK, BT_CONNECT) &&
> > !test_bit(HCI_INQUIRY, &hdev->flags) in hci_conn_check_pending() before
> > we actually retry, to make sure the retry counter doesn't get
> > incremented wrongly. I'll give that a try.
>
> Perhaps I'm missing something, but it should be possible to block
> concurrent access to HCI while a command is pending with use of
> hci_cmd_sync, at least on LE we do that by waiting the connection
> complete event so connection attempts are serialized but we don't seem
> to be doing the same for BR/EDR.

That's a good point, it might even allow for a nice little cleanup 
because we can then cancel inquiries in hci_acl_create_connection() 
synchronously, too.

Question is just whether there's any devices out there that actually do 
support paging with more than a single device at a time and if we want 
to support that?

> > > > Signed-off-by: Jonas Dreßler <verdre@xxxxxxx>
> > > > ---
> > > >    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
> >
> > Cheers,
> > Jonas
>
>
>
> --
> Luiz Augusto von Dentz