Message-ID: <CABBYNZJZ8cA77FBgvXWJeVjVpzjuwzC4Mn4QRR3OsZJn+M=VyQ@mail.gmail.com>
Date: Mon, 8 Jan 2024 15:46:22 -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 v2 4/4] Bluetooth: Remove pending ACL connection attempts

Hi Jonas,

On Mon, Jan 8, 2024 at 3:26 PM Jonas Dreßler <verdre@...d.nl> wrote:
>
> Hi Luiz,
>
> On 1/8/24 20:41, Luiz Augusto von Dentz wrote:
> > Hi Jonas,
> >
> > On Mon, Jan 8, 2024 at 2:29 PM Jonas Dreßler <verdre@...d.nl> wrote:
> >>
> >> Hi Luiz,
> >>
> >> On 1/8/24 20:14, Luiz Augusto von Dentz wrote:
> >>> Hi Jonas,
> >>>
> >>> On Mon, Jan 8, 2024 at 1:55 PM Jonas Dreßler <verdre@...d.nl> wrote:
> >>>>
> >>>> On 1/8/24 19:44, Jonas Dreßler wrote:
> >>>>> On 1/8/24 19:39, Jonas Dreßler wrote:
> >>>>>> With the last commit we moved to using the hci_sync queue for "Create
> >>>>>> Connection" requests, removing the need for retrying the paging after
> >>>>>> finished/failed "Create Connection" requests and after the end of
> >>>>>> inquiries.
> >>>>>>
> >>>>>> hci_conn_check_pending() was used to trigger this retry, we can remove it
> >>>>>> now.
> >>>>>>
> >>>>>> Note that we can also remove the special handling for COMMAND_DISALLOWED
> >>>>>> errors in the completion handler of "Create Connection", because "Create
> >>>>>> Connection" requests are now always serialized.
> >>>>>>
> >>>>>> This is somewhat reverting commit 4c67bc74f016 ("[Bluetooth] Support
> >>>>>> concurrent connect requests").
> >>>>>>
> >>>>>> With this, the BT_CONNECT2 state of ACL hci_conn objects should now be
> >>>>>> back to meaning only one thing: That we received a connection request
> >>>>>> from another device (see hci_conn_request_evt), but the actual connect
> >>>>>> should be deferred.
> >>>>>> ---
> >>>>>>     include/net/bluetooth/hci_core.h |  1 -
> >>>>>>     net/bluetooth/hci_conn.c         | 16 ----------------
> >>>>>>     net/bluetooth/hci_event.c        | 21 ++++-----------------
> >>>>>>     3 files changed, 4 insertions(+), 34 deletions(-)
> >>>>>>
> >>>>>> diff --git a/include/net/bluetooth/hci_core.h
> >>>>>> b/include/net/bluetooth/hci_core.h
> >>>>>> index 2c30834c1..d7483958d 100644
> >>>>>> --- a/include/net/bluetooth/hci_core.h
> >>>>>> +++ b/include/net/bluetooth/hci_core.h
> >>>>>> @@ -1330,7 +1330,6 @@ struct hci_conn *hci_conn_add(struct hci_dev
> >>>>>> *hdev, int type, bdaddr_t *dst,
> >>>>>>                       u8 role);
> >>>>>>     void hci_conn_del(struct hci_conn *conn);
> >>>>>>     void hci_conn_hash_flush(struct hci_dev *hdev);
> >>>>>> -void hci_conn_check_pending(struct hci_dev *hdev);
> >>>>>>     struct hci_chan *hci_chan_create(struct hci_conn *conn);
> >>>>>>     void hci_chan_del(struct hci_chan *chan);
> >>>>>> diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
> >>>>>> index 541d55301..22033057b 100644
> >>>>>> --- a/net/bluetooth/hci_conn.c
> >>>>>> +++ b/net/bluetooth/hci_conn.c
> >>>>>> @@ -2534,22 +2534,6 @@ void hci_conn_hash_flush(struct hci_dev *hdev)
> >>>>>>         }
> >>>>>>     }
> >>>>>> -/* Check pending connect attempts */
> >>>>>> -void hci_conn_check_pending(struct hci_dev *hdev)
> >>>>>> -{
> >>>>>> -    struct hci_conn *conn;
> >>>>>> -
> >>>>>> -    BT_DBG("hdev %s", hdev->name);
> >>>>>> -
> >>>>>> -    hci_dev_lock(hdev);
> >>>>>> -
> >>>>>> -    conn = hci_conn_hash_lookup_state(hdev, ACL_LINK, BT_CONNECT2);
> >>>>>> -    if (conn)
> >>>>>> -        hci_cmd_sync_queue(hdev, hci_acl_create_connection_sync,
> >>>>>> conn, NULL);
> >>>>>> -
> >>>>>> -    hci_dev_unlock(hdev);
> >>>>>> -}
> >>>>>> -
> >>>>>>     static u32 get_link_mode(struct hci_conn *conn)
> >>>>>>     {
> >>>>>>         u32 link_mode = 0;
> >>>>>> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> >>>>>> index e8b4a0126..91973d6d1 100644
> >>>>>> --- a/net/bluetooth/hci_event.c
> >>>>>> +++ b/net/bluetooth/hci_event.c
> >>>>>> @@ -117,8 +117,6 @@ static u8 hci_cc_inquiry_cancel(struct hci_dev
> >>>>>> *hdev, void *data,
> >>>>>>             hci_discovery_set_state(hdev, DISCOVERY_STOPPED);
> >>>>>>         hci_dev_unlock(hdev);
> >>>>>> -    hci_conn_check_pending(hdev);
> >>>>>> -
> >>>>>>         return rp->status;
> >>>>>>     }
> >>>>>> @@ -149,8 +147,6 @@ static u8 hci_cc_exit_periodic_inq(struct hci_dev
> >>>>>> *hdev, void *data,
> >>>>>>         hci_dev_clear_flag(hdev, HCI_PERIODIC_INQ);
> >>>>>> -    hci_conn_check_pending(hdev);
> >>>>>> -
> >>>>>>         return rp->status;
> >>>>>>     }
> >>>>>> @@ -2296,10 +2292,8 @@ static void hci_cs_inquiry(struct hci_dev
> >>>>>> *hdev, __u8 status)
> >>>>>>     {
> >>>>>>         bt_dev_dbg(hdev, "status 0x%2.2x", status);
> >>>>>> -    if (status) {
> >>>>>> -        hci_conn_check_pending(hdev);
> >>>>>> +    if (status)
> >>>>>>             return;
> >>>>>> -    }
> >>>>>>         set_bit(HCI_INQUIRY, &hdev->flags);
> >>>>>>     }
> >>>>>> @@ -2323,12 +2317,9 @@ 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) {
> >>>>>> -                conn->state = BT_CLOSED;
> >>>>>> -                hci_connect_cfm(conn, status);
> >>>>>> -                hci_conn_del(conn);
> >>>>>> -            } else
> >>>>>> -                conn->state = BT_CONNECT2;
> >>>>>> +            conn->state = BT_CLOSED;
> >>>>>> +            hci_connect_cfm(conn, status);
> >>>>>> +            hci_conn_del(conn);
> >>>>>>             }
> >>>>>>         } else {
> >>>>>>             if (!conn) {
> >>>>>> @@ -3020,8 +3011,6 @@ static void hci_inquiry_complete_evt(struct
> >>>>>> hci_dev *hdev, void *data,
> >>>>>>         bt_dev_dbg(hdev, "status 0x%2.2x", ev->status);
> >>>>>> -    hci_conn_check_pending(hdev);
> >>>>>> -
> >>>>>>         if (!test_and_clear_bit(HCI_INQUIRY, &hdev->flags))
> >>>>>>             return;
> >>>>>> @@ -3247,8 +3236,6 @@ static void hci_conn_complete_evt(struct hci_dev
> >>>>>> *hdev, void *data,
> >>>>>>     unlock:
> >>>>>>         hci_dev_unlock(hdev);
> >>>>>> -
> >>>>>> -    hci_conn_check_pending(hdev);
> >>>>>>     }
> >>>>>>     static void hci_reject_conn(struct hci_dev *hdev, bdaddr_t *bdaddr)
> >>>>>
> >>>>> Please take a special look at this one: I'm not sure if I'm breaking the
> >>>>> functionality of deferred connecting using BT_CONNECT2 in
> >>>>> hci_conn_request_evt() here, as I don't see anywhere where we check for
> >>>>> this state and establish a connection later.
> >>>>>
> >>>>> It seems that this is how hci_conn_request_evt() was initially written
> >>>>> though, hci_conn_check_pending() only got introduced later and seems
> >>>>> unrelated.
> >>>>
> >>>> Ahh nevermind... The check for BT_CONNECT2 on "Conn Complete event" got
> >>>> introduced with 4c67bc74f01 ([Bluetooth] Support concurrent connect
> >>>> requests). And later the deferred connection setup on "Conn Request
> >>>> event" got introduced with 20714bfef8 ("Bluetooth: Implement deferred
> >>>> sco socket setup").
> >>>>
> >>>> I assume the latter commit was relying on the "Create Connection"
> >>>> request "Conn Complete event" that got introduced with the former commit
> >>>> then? That would imply that we use BT_CONNECT2 if there's already a
> >>>> "Create Connection" going on when the "Conn Request event" happens, and
> >>>> we must wait for that existing request to finish.. Is that how those
> >>>> deferred connections are supposed to work?
> >>>
> >>> Well if you are not sure that works we better make sure we have tests
> >>> that cover this, for LE I know for sure it works because we have the
> >>> likes of iso-tester that do connect 2 peers simultaneously, but for
> >>> classic I don't recall having any test that does multiple connections.
> >>
> >> The sequential "Create Connection" logic works, I tested that (of course
> >> I'm happy to add tests if it's not too much work).
> >>
> >> What I'm unsure about is if and how incoming connection requests from
> >> other devices with HCI_PROTO_DEFER flag are supposed to work and whether
> >> they are meant to trigger a "Create Connection" from us?
> >
> > For incoming connections on Classic that should result in an
> > accept/reject connection command, so it should cause another Create
> > Connection if that is what you are afraid of.
> >
>
> Hmm, do you mean it *shouldn't* cause another "Create Connection"?

Yeah, sorry about that, it is Monday I should probably double check if
what I wrote makes any sense before sending :D

> I just checked in the spec: It sounds like once we send the "Accept
> Connection Request" to the controller, the controller takes care of
> establishing the connection by itself (no "Create Connection"
> necessary), and will then later give us a "Connection Complete" event to
> indicate that the connection is done.

Yep, it will follow up with a Connection Complete.

> If I'm reading all this correctly, that sounds like my commit is
> correct, and we had a bug in this logic before by interpreting
> BT_CONNECT2 in two different ways.
>
> >>>
> >>>>>
> >>>>> Thanks,
> >>>>> Jonas
> >>>
> >>>
> >>>
> >
> >
> >



-- 
Luiz Augusto von Dentz

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