Re: [PATCH v4 2/4] Bluetooth: Rework le_scan_restart for hci_sync

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Hi Stefan, Brian,

On Tue, Aug 29, 2023 at 6:27 AM Stefan Agner <stefan@xxxxxxxx> wrote:
>
> Hi Thorsten,
>
> No, this hasn't been addressed so far. I am also not sure how we can
> help solving that particular issue.
>
> Besides this, we have other Bluetooth issues which seem to be Kernel
> regressions (where downgrading to Linux 5.15 also helps), folks see
> "hci0: unexpected event for opcode" on Intel but also other systems. We
> haven't bisected that issue yet. But it seems that the Bluetooth stack
> is really somewhat unstable in recent releases.


I suspect the following change shall make it behave as before, the use
of hci_cmd_sync_queue is not equivalent to hci_req_sync:

https://gist.github.com/Vudentz/b78f34e3775c8cd2db55b868e5c8ef42

That said, I'm considering removing the whole custom handling for
HCI_QUIRK_STRICT_DUPLICATE_FILTER and just disable duplicate filtering
when this flag is set.

> --
> Stefan
>
>
> On 2023-08-29 13:22, Linux regression tracking (Thorsten Leemhuis)
> wrote:
> > Hi, Thorsten here, the Linux kernel's regression tracker. Top-posting
> > for once, to make this easily accessible to everyone.
> >
> > Stefan, was this regression ever addressed? Doesn't look like it from
> > here, but maybe I'm missing something.
> >
> > Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
> > --
> > Everything you wanna know about Linux kernel regression tracking:
> > https://linux-regtracking.leemhuis.info/about/#tldr
> > If I did something stupid, please tell me, as explained on that page.
> >
> > #regzbot poke
> >
> > On 30.06.23 12:59, Stefan Agner wrote:
> >> Hi Brian,
> >>
> >> Gentle ping on the issue below.
> >>
> >> On 2023-06-20 16:41, Stefan Agner wrote:
> >>> On 2023-06-16 03:22, Brian Gix wrote:
> >>>
> >>>> On Thu, Jun 15, 2023 at 11:28 AM Luiz Augusto von Dentz <luiz.dentz@xxxxxxxxx> wrote:
> >>>>
> >>>>> +Brian Gix
> >>>>>
> >>>>> On Thu, Jun 15, 2023 at 10:27 AM Luiz Augusto von Dentz
> >>>>> <luiz.dentz@xxxxxxxxx> wrote:
> >>>>>>
> >>>>>> Hi Stefan,
> >>>>>>
> >>>>>> On Thu, Jun 15, 2023 at 5:06 AM Stefan Agner <stefan@xxxxxxxx> wrote:
> >>>>>>>
> >>>>>>> Hi Brian, hi all,
> >>>>>>>
> >>>>>>> We experienced quite some Bluetooth issues after moving from Linux 5.15
> >>>>>>> to 6.1 on Home Assistant OS, especially on Intel NUC type systems (which
> >>>>>>> is a popular choice in our community, so it might just be that). When
> >>>>>>> continuously scanning/listening for BLE packets, the packet flow
> >>>>>>> suddenly ends. Depending on which and how many devices (possibly also
> >>>>>>> other factors) within minutes or hours.
> >>>>>>>
> >>>>>>> Jan (in cc) was able to bisect the issue, and was able to pinpoint the
> >>>>>>> problem to this change.
> >>>>>>>
> >>>>>>> Meanwhile I was able to confirm, that reverting this single commit on
> >>>>>>> the latest 6.1.34 seems to resolve the issue.
> >>>>>>>
> >>>>>>> I've reviewed the change and surrounding code, and one thing I've
> >>>>>>> noticed is that the if statement to set cp.filter_dup in
> >>>>>>> hci_le_set_ext_scan_enable_sync and hci_le_set_scan_enable_sync are
> >>>>>>> different. Not sure if that needs to be the way it is, but my outside
> >>>>>>> gut feeling says hci_le_set_ext_scan_enable_sync should use "if (val &&
> >>>>>>> hci_dev_test_flag(hdev, HCI_MESH))" as well.
> >>>>>>>
> >>>>>>> However, that did not fix the problem (but maybe it is wrong
> >>>>>>> nonetheless?).
> >>>>>>>
> >>>>>>> Anyone has an idea what could be the problem here?
> >>>>>>
> >>>>>> Are there any logs of the problem? Does any HCI command fails or
> >>>>>> anything so that we can track down what could be wrong?
> >>>
> >>> No HCI command fails, there is also no issue reported in the kernel log.
> >>> BlueZ just stops receiving BLE packets, at least from certain devices.
> >>>
> >>>>>
> >>>>> @Brian Gix perhaps you have a better idea what is going wrong here?
> >>>>
> >>>> It seems unlikely that this is Mesh related. Mesh does need for filtering to
> >>>> be FALSE, and Mesh does not use extended scanning in any case.
> >>>>
> >>>> But this was part of the final rewrite to retire the hci_req mechanism in
> >>>> favor of the hci_sync mechanism. So my best guess off the top of my head is
> >>>> that there was an unintended race condition that worked better than the
> >>>> synchronous single-threading mechanism?  Filtering (or not) should not
> >>>
> >>> After review the code I concluded the same. What is a bit surprising to
> >>> me is that it is so well reproducible. I guess it is nicer to have a
> >>> reproducible one than a hard to reproduce one :)
> >>>
> >>>> prevent advertising packets from permanently wedging.  Does anyone have an
> >>>> HCI flow log with and without the offending patch?  Ideally they should be
> >>>> identical...  If they are not then I obviously did something wrong. As this
> >>>> was not specifically Mesh related, I may have missed some non-mesh corner
> >>>> cases.
> >>>
> >>>
> >>> I've taken two btmon captures, I created them using:
> >>> btmon -i hci0 -w /config/hcidump-hci-req-working.log
> >>>
> >>> You can find them at:
> >>> https://os-builds.home-assistant.io/hcidump-hci-req-working.log
> >>> https://os-builds.home-assistant.io/hcidump-hci-sync-non-working.log
> >>
> >> Could you gain any insights from these logs?
> >>
> >> --
> >> Stefan
> >>
> >>
> >>>
> >>> This is while running our user space software (Home Assistant with
> >>> Bluetooth integration). Besides some BLE devices (e.g. Xioami Mi
> >>> Temperature & Humidity sensor) I have a ESP32 running which sends SPAM
> >>> advertisements every 100ms (this accelerates the issue). In the
> >>> non-working case you'll see that the system doesn't receive any SPAM
> >>> advertisements after around 27 seconds. The working log shows that it
> >>> continuously receives the same packets (capture 120s).
> >>>
> >>> Hope this helps.
> >>>
> >>> --
> >>> Stefan
> >>>
> >>>
> >>
> >>



-- 
Luiz Augusto von Dentz




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