linux-kernel - Re: Sometimes DVB broken with commit 6769a0b7ee0c3b

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Date:   Mon, 5 Jun 2023 12:44:43 +0200
From:   Thorsten Leemhuis <regressions@...mhuis.info>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     Linux regressions mailing list <regressions@...ts.linux.dev>,
        Hyunwoo Kim <imv4bel@...il.com>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Thomas Voegtle <tv@...96.de>, linux-kernel@...r.kernel.org
Subject: Re: Sometimes DVB broken with commit 6769a0b7ee0c3b

On 05.06.23 12:37, Mauro Carvalho Chehab wrote:
> Em Mon, 5 Jun 2023 11:38:49 +0200
> "Linux regression tracking (Thorsten Leemhuis)" <regressions@...mhuis.info> escreveu:
> 
>> Hi, Thorsten here, the Linux kernel's regression tracker.
>>
>> On 30.05.23 13:12, Thomas Voegtle wrote:
>>>
>>> I have the problem that sometimes my DVB card does not initialize
>>> properly booting Linux 6.4-rc4.
>>> This is not always, maybe in 3 out of 4 attempts.
>>> When this happens somehow you don't see anything special in dmesg, but
>>> the card just doesn't work.
>>>
>>> Reverting this helps:
>>> commit 6769a0b7ee0c3b31e1b22c3fadff2bfb642de23f
>>> Author: Hyunwoo Kim <imv4bel@...il.com>
>>> Date:   Thu Nov 17 04:59:22 2022 +0000
>>>
>>>     media: dvb-core: Fix use-after-free on race condition at dvb_frontend
>>>
>>>
>>> I have:
>>> 03:00.0 Multimedia video controller [0400]: Conexant Systems, Inc.
>>> CX23887/8
>>> PCIe Broadcast Audio and Video Decoder with 3D Comb [14f1:8880] (rev 04)
>>>         Subsystem: Hauppauge computer works Inc. Device [0070:c138]
>>>         Kernel driver in use: cx23885  
>>
>> Hmmm, that was posted last Tuesday and received not a single reply. :-/
>>
>> Hyunwoo Kim: could you please look at it, as it's a regression caused by
>> a commit of yours (one that would be good to solve before 6.4 is
>> finalized!)? And in case you are unable to do so let us know?
>>
>> But FWIW:
>>
>> Mauro: I wonder if this is something you or someone else has to look
>> into, as Hyunwoo Kim posted a few times per months to Linux lists, but
>> according  to a quick search on lore hasn't posted anything since ~two
>> months now. :-/
> 
> Yeah, I was slow applying this one, as I was afraid of it to cause
> troubles. The DVB frontend state machine is complex, and uses a
> semaphore to update its state. There was some past attempts of
> addressing some lifetime issues there that we ended needing to revert
> or not being applied, as the fix caused more harm than good.
> [...]

Thx for the update. That's unfortunate, but how it is sometimes. Which
leads to a follow-up question: is reverting the culprit temporarily an
option? Or did those old use-after-free problems became known to be a
problem we can't live with anymore for another few months?

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.