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Message-ID: <CABBYNZJu-LY1kBQCa6cMJyxMQ2PU8PGT-B_qgy56quZAFSjChg@mail.gmail.com>
Date: Fri, 27 Jun 2025 11:03:20 -0400
From: Luiz Augusto von Dentz <luiz.dentz@...il.com>
To: Yang Li <yang.li@...ogic.com>
Cc: Pauli Virtanen <pav@....fi>, Marcel Holtmann <marcel@...tmann.org>, 
	Johan Hedberg <johan.hedberg@...il.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Simon Horman <horms@...nel.org>, linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Bluetooth: hci_event: Add support for handling LE BIG
 Sync Lost event

Hi,

On Fri, Jun 27, 2025 at 7:31 AM Yang Li <yang.li@...ogic.com> wrote:
>
> Hi Luiz,
> > [ EXTERNAL EMAIL ]
> >
> > Hi Yang,
> >
> > On Thu, Jun 26, 2025 at 1:54 AM Yang Li <yang.li@...ogic.com> wrote:
> >> Hi Pauli,
> >>> [ EXTERNAL EMAIL ]
> >>>
> >>> Hi,
> >>>
> >>> ke, 2025-06-25 kello 16:42 +0800, Yang Li via B4 Relay kirjoitti:
> >>>> From: Yang Li <yang.li@...ogic.com>
> >>>>
> >>>> When the BIS source stops, the controller sends an LE BIG Sync Lost
> >>>> event (subevent 0x1E). Currently, this event is not handled, causing
> >>>> the BIS stream to remain active in BlueZ and preventing recovery.
> >>>>
> >>>> Signed-off-by: Yang Li <yang.li@...ogic.com>
> >>>> ---
> >>>> Changes in v2:
> >>>> - Matching the BIG handle is required when looking up a BIG connection.
> >>>> - Use ev->reason to determine the cause of disconnection.
> >>>> - Call hci_conn_del after hci_disconnect_cfm to remove the connection entry
> >>>> - Delete the big connection
> >>>> - Link to v1: https://lore.kernel.org/r/20250624-handle_big_sync_lost_event-v1-1-c32ce37dd6a5@amlogic.com
> >>>> ---
> >>>>    include/net/bluetooth/hci.h |  6 ++++++
> >>>>    net/bluetooth/hci_event.c   | 31 +++++++++++++++++++++++++++++++
> >>>>    2 files changed, 37 insertions(+)
> >>>>
> >>>> diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
> >>>> index 82cbd54443ac..48389a64accb 100644
> >>>> --- a/include/net/bluetooth/hci.h
> >>>> +++ b/include/net/bluetooth/hci.h
> >>>> @@ -2849,6 +2849,12 @@ struct hci_evt_le_big_sync_estabilished {
> >>>>         __le16  bis[];
> >>>>    } __packed;
> >>>>
> >>>> +#define HCI_EVT_LE_BIG_SYNC_LOST 0x1e
> >>>> +struct hci_evt_le_big_sync_lost {
> >>>> +     __u8    handle;
> >>>> +     __u8    reason;
> >>>> +} __packed;
> >>>> +
> >>>>    #define HCI_EVT_LE_BIG_INFO_ADV_REPORT       0x22
> >>>>    struct hci_evt_le_big_info_adv_report {
> >>>>         __le16  sync_handle;
> >>>> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> >>>> index 66052d6aaa1d..d0b9c8dca891 100644
> >>>> --- a/net/bluetooth/hci_event.c
> >>>> +++ b/net/bluetooth/hci_event.c
> >>>> @@ -7026,6 +7026,32 @@ static void hci_le_big_sync_established_evt(struct hci_dev *hdev, void *data,
> >>>>         hci_dev_unlock(hdev);
> >>>>    }
> >>>>
> >>>> +static void hci_le_big_sync_lost_evt(struct hci_dev *hdev, void *data,
> >>>> +                                         struct sk_buff *skb)
> >>>> +{
> >>>> +     struct hci_evt_le_big_sync_lost *ev = data;
> >>>> +     struct hci_conn *bis, *conn;
> >>>> +
> >>>> +     bt_dev_dbg(hdev, "big handle 0x%2.2x", ev->handle);
> >>>> +
> >>>> +     hci_dev_lock(hdev);
> >>>> +
> >>>> +     list_for_each_entry(bis, &hdev->conn_hash.list, list) {
> >>> This should check bis->type == BIS_LINK too.
> >> Will do.
> >>>> +             if (test_and_clear_bit(HCI_CONN_BIG_SYNC, &bis->flags) &&
> >>>> +                 (bis->iso_qos.bcast.big == ev->handle)) {
> >>>> +                     hci_disconn_cfm(bis, ev->reason);
> >>>> +                     hci_conn_del(bis);
> >>>> +
> >>>> +                     /* Delete the big connection */
> >>>> +                     conn = hci_conn_hash_lookup_pa_sync_handle(hdev, bis->sync_handle);
> >>>> +                     if (conn)
> >>>> +                             hci_conn_del(conn);
> >>> Problems:
> >>>
> >>> - use after free
> >>>
> >>> - hci_conn_del() cannot be used inside list_for_each_entry()
> >>>     of the connection list
> >>>
> >>> - also list_for_each_entry_safe() allows deleting only the iteration
> >>>     cursor, so some restructuring above is needed
> >> Following your suggestion, I updated the hci_le_big_sync_lost_evt function.
> >>
> >> +static void hci_le_big_sync_lost_evt(struct hci_dev *hdev, void *data,
> >> +                                           struct sk_buff *skb)
> >> +{
> >> +       struct hci_evt_le_big_sync_lost *ev = data;
> >> +       struct hci_conn *bis, *conn, *n;
> >> +
> >> +       bt_dev_dbg(hdev, "big handle 0x%2.2x", ev->handle);
> >> +
> >> +       hci_dev_lock(hdev);
> >> +
> >> +       /* Delete the pa sync connection */
> >> +       bis = hci_conn_hash_lookup_pa_sync_big_handle(hdev, ev->handle);
> >> +       if (bis) {
> >> +               conn = hci_conn_hash_lookup_pa_sync_handle(hdev,
> >> bis->sync_handle);
> >> +               if (conn)
> >> +                       hci_conn_del(conn);
> >> +       }
> >> +
> >> +       /* Delete each bis connection */
> >> +       list_for_each_entry_safe(bis, n, &hdev->conn_hash.list, list) {
> >> +               if (bis->type == BIS_LINK &&
> >> +                   bis->iso_qos.bcast.big == ev->handle &&
> >> +                   test_and_clear_bit(HCI_CONN_BIG_SYNC, &bis->flags)) {
> >> +                       hci_disconn_cfm(bis, ev->reason);
> >> +                       hci_conn_del(bis);
> >> +               }
> >> +       }
> > Id follow the logic in hci_le_create_big_complete_evt, so you do something like:
> >
> >      while ((conn = hci_conn_hash_lookup_big_state(hdev, ev->handle,
> >                                BT_CONNECTED)))...
> >
> > That way we don't operate on the list cursor, that said we may need to
> > add the role as parameter to hci_conn_hash_lookup_big_state, because
> > the BIG id domain is role specific so we can have clashes if there are
> > Broadcast Sources using the same BIG id the above would return them as
> > well and even if we check for the role inside the while loop will keep
> > returning it forever.
>
> I updated the patch according to your suggestion; however, during testing, it resulted in a system panic.

What is the backtrace?

> hci_conn_hash_lookup_big_state(struct hci_dev *hdev, __u8 handle,  __u16 state)
>
>          list_for_each_entry_rcu(c, &h->list, list) {
>                  if (c->type != BIS_LINK || bacmp(&c->dst, BDADDR_ANY) ||
> +                       c->role != HCI_ROLE_SLAVE ||
>                      c->state != state)
>                          continue;

It needs to be passed as an argument not just change the role
internally otherwise it will break the existing users of it.

> +static void hci_le_big_sync_lost_evt(struct hci_dev *hdev, void *data,
> +                                           struct sk_buff *skb)
> +{
> +       struct hci_evt_le_big_sync_lost *ev = data;
> +       struct hci_conn *bis, *conn;
> +
> +       bt_dev_dbg(hdev, "big handle 0x%2.2x", ev->handle);
> +
> +       hci_dev_lock(hdev);
> +
> +       /* Delete the pa sync connection */
> +       bis = hci_conn_hash_lookup_pa_sync_big_handle(hdev, ev->handle);
> +       if (bis) {
> +               conn = hci_conn_hash_lookup_pa_sync_handle(hdev, bis->sync_handle);
> +               if (conn)
> +                       hci_conn_del(conn);
> +       }
> +
> +       /* Delete each bis connection */
> +       while ((bis = hci_conn_hash_lookup_big_state(hdev, ev->handle,
> +                                                       BT_CONNECTED))) {
> +               clear_bit(HCI_CONN_BIG_SYNC, &bis->flags);
> +               hci_disconn_cfm(bis, ev->reason);
> +               hci_conn_del(bis);
> +       }
> +
> +       hci_dev_unlock(hdev);
> +}
>
> However, during testing, I encountered some issues:
>
> 1. The current BIS connections all have the state BT_OPEN (2).

Hmm, that doesn't sound right, if the BIG Sync has been completed the
BIS connection shall be moved to BT_CONNECTED. Looks like we are not
marking it as connected:

hci_le_big_sync_established_evt (Broadcast Sink):

        set_bit(HCI_CONN_BIG_SYNC, &bis->flags);
       hci_iso_setup_path(bis);

hci_le_create_big_complete_evt (Broadcast Source):

        conn->state = BT_CONNECTED;
        set_bit(HCI_CONN_BIG_CREATED, &conn->flags);
        hci_debugfs_create_conn(conn);
        hci_conn_add_sysfs(conn);
        hci_iso_setup_path(conn);

> [  131.813237][1 T1967  d.] list conn 00000000fd2e0fb2, handle 0x0010,
> state 1 #LE link
> [  131.813439][1 T1967  d.] list conn 00000000553bfedc, handle 0x0f01,
> state 2  #PA link
> [  131.814301][1 T1967  d.] list conn 0000000074213ccb, handle 0x0100,
> state 2 #bis1 link
> [  131.815167][1 T1967  d.] list conn 00000000ee6adb18, handle 0x0101,
> state 2 #bis2 link
>
> 2. hci_conn_hash_lookup_big_state() fails to find the corresponding BIS
> connection even when the state is set to OPEN.
>
> Therefore, I’m considering reverting to the original patch, but adding a
> role check as an additional condition.
> What do you think?
>
> +       /* Delete each bis connection */
> +       list_for_each_entry_safe(bis, n, &hdev->conn_hash.list, list) {
> +               if (bis->type == BIS_LINK &&
> +                   bis->role == HCI_ROLE_SLAVE &&
> +                   bis->iso_qos.bcast.big == ev->handle &&
> +                   test_and_clear_bit(HCI_CONN_BIG_SYNC, &bis->flags)) {
> +                       hci_disconn_cfm(bis, ev->reason);
> +                       hci_conn_del(bis);
> +               }
> +       }
>
> >
> >> +
> >> +       hci_dev_unlock(hdev);
> >> +}
> >>
> >>>> +             }
> >>>> +     }
> >>>> +
> >>>> +     hci_dev_unlock(hdev);
> >>>> +}
> >>>> +
> >>>>    static void hci_le_big_info_adv_report_evt(struct hci_dev *hdev, void *data,
> >>>>                                            struct sk_buff *skb)
> >>>>    {
> >>>> @@ -7149,6 +7175,11 @@ static const struct hci_le_ev {
> >>>>                      hci_le_big_sync_established_evt,
> >>>>                      sizeof(struct hci_evt_le_big_sync_estabilished),
> >>>>                      HCI_MAX_EVENT_SIZE),
> >>>> +     /* [0x1e = HCI_EVT_LE_BIG_SYNC_LOST] */
> >>>> +     HCI_LE_EV_VL(HCI_EVT_LE_BIG_SYNC_LOST,
> >>>> +                  hci_le_big_sync_lost_evt,
> >>>> +                  sizeof(struct hci_evt_le_big_sync_lost),
> >>>> +                  HCI_MAX_EVENT_SIZE),
> >>>>         /* [0x22 = HCI_EVT_LE_BIG_INFO_ADV_REPORT] */
> >>>>         HCI_LE_EV_VL(HCI_EVT_LE_BIG_INFO_ADV_REPORT,
> >>>>                      hci_le_big_info_adv_report_evt,
> >>>>
> >>>> ---
> >>>> base-commit: bd35cd12d915bc410c721ba28afcada16f0ebd16
> >>>> change-id: 20250612-handle_big_sync_lost_event-4c7dc64390a2
> >>>>
> >>>> Best regards,
> >>> --
> >>> Pauli Virtanen
> >
> >
> > --
> > Luiz Augusto von Dentz



-- 
Luiz Augusto von Dentz

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