Re: [BUG] BLE device unpairing triggers kernel panic

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hi Luiz,

On 17.06.22 22:48, Luiz Augusto von Dentz wrote:
> On Thu, Jun 16, 2022 at 3:38 AM Ahmad Fatoum <a.fatoum@pengutronix.de> wrote:
>> On 16.05.22 18:37, Ahmad Fatoum wrote:
>>>>>> - Commit a56a1138cbd8 ("Bluetooth: hci_sync: Fix not using conn_timeout")
>>>>>>   fixes, despite the title, what event is waited on. First Pairing works now,
>>>>>>   but the second pairing times out and crashes the kernel:
>>>>>>
>>>>>>   [   84.191684] Bluetooth: hci0: Opcode 0x200d failed: -110
>>>>>>   [   84.230478] Bluetooth: hci0: request failed to create LE connection: err -110
>>>>>>   [   84.237690] Unable to handle kernel read from unreadable memory at virtual address 0000000000000ca8
>>>>
>>>> That said the error -110 mean -ETIMEDOUT
>>>
>>> Yes, this issue remains still. I feel better about my revert
>>> knowing that the crash is fixed, but I'd like this regression
>>> here fixed upstream as well. I'll try to collect some more
>>> information and report back.
>>
>> I've now found time to revisit this and sprinkle around some
>> extra logging. This is the initial pairing that works:
>>
>>   Bluetooth: entered hci_le_create_conn_sync()
>>   Bluetooth: hci0: opcode 0x200d plen 25
>>   Bluetooth: hci0: event 0x0f (sent = 0x0a)
>>   Bluetooth: hci0: BT: opcode 0x200d (sent: 0x0a)
>>   Bluetooth: hci0: event 0x3e (sent = 0x0a)
>>   Bluetooth: hci0: BT: subevent 0x0a (sent 0x0a)
>>   Bluetooth: entered hci_le_meta_evt(event=0x0a) completion clause
>>
>> I unpaired on device side and then retried pairing:
>>
>>   Bluetooth: entered hci_le_create_conn_sync()
>>   Bluetooth: hci0: opcode 0x200d plen 25
>>   Bluetooth: hci0: event 0x0f (sent = 0x0a)
>>   Bluetooth: hci0: BT: opcode 0x200d (sent: 0x0a)
>>   Bluetooth: entered hci_abort_conn()
>>   Bluetooth: hci0: opcode hci_req_add_ev 0x200e
>>   Bluetooth: hci0: event 0x0e (sent = 0x00)
>>   Bluetooth: hci0: event 0x3e (sent = 0x00)
>>   Bluetooth: hci0: BT: subevent 0x0a (sent 0x00)
>>   Bluetooth: __hci_cmd_sync_sk pending (event = 0x0a status=1, err=-110)
>>   Bluetooth: hci0: Opcode 0x200d failed: -110
>>   Bluetooth: hci0: opcode 0x2006 plen 15
>>   Bluetooth: hci0: event 0x0e (sent = 0x00)
>>   Bluetooth: hci0: opcode 0x200a plen 1
>>   Bluetooth: hci0: event 0x0e (sent = 0x00)
>>   Bluetooth: hci0: request failed to create LE connection: err -110
>>
>>
>> But now it times out as reported. It looks like the
>> intermittent hci_abort_conn() is at fault here. My theory is
>> that replacing hci->sent_cmd is the problem here, as other
>> events can't be matched anymore.
> 
> Yep, unpair command uses hci_abort_conn when it should really be using
> hci_abort_conn_sync, the problem is if we do that then it probably no
> longer work because it would have to wait for sync queue to complete
> so it would only be able to disconnect after the connect command
> completes, well perhaps that is acceptable

Disconnect of connection #1 being processed after new connection #2
concluded sounds wrong. Would I be able to reconnect
afterwards or would all connections, but the first, be directly
disconnected...?

> otherwise we need a
> different queue to handle command that abort/cancel other already in
> the queue.

Is the revert an acceptable interim solution or are there issues
I am missing?

Cheers,
Ahmad

> 
>> We've been deploying the revert for a while now and I just posted
>> it to the mailing list[1]. There have been other reports
>> of this issue with different hardware too and fixing sent_cmd
>> would likely be too complicated/time intensive for me.
>>
>> I am happy to test future patches that fix this properly though.
>>
>> [1]: https://lore.kernel.org/linux-bluetooth/20220616092418.738877-1-a.fatoum@pengutronix.de/T/#t
>>
>> Cheers,
>> Ahmad
>>
>>
>>
>>>
>>> Cheers,
>>> Ahmad
>>>
>>
>>
>> --
>> Pengutronix e.K.                           |                             |
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> 
> 
> 


-- 
Pengutronix e.K.                           |                             |
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