linux-kernel - Re: [PATCH v2 0/2] drivercore: deferral race condition fix

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Message-ID: <CACxGe6sJtEeMOx+qMws2BCC4tuHMnWRAZv9NkEPADAtXAvtM4g@mail.gmail.com>
Date:	Thu, 24 Apr 2014 22:01:02 +0100
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Peter Ujfalusi <peter.ujfalusi@...com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mark Brown <broonie@...nel.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/2] drivercore: deferral race condition fix

On Thu, Apr 24, 2014 at 8:31 AM, Peter Ujfalusi <peter.ujfalusi@...com> wrote:
> Hi Greg, Grant,
>
> On 04/09/2014 01:52 PM, Peter Ujfalusi wrote:
>> Hi,
>>
>> Changes since v1:
>> - The deferral race detection and handling has been moved to
>>   driver_deferred_probe_trigger() and driver_deferred_probe_add() functions with
>>   comment section.
>> - driver_deferred_probe_add/del function needed to be moved. Both of them placed
>>   after driver_deferred_probe_trigger() so they remain together.
>> - I have not added the Acked-by from Mark and Grant since the patch itself
>>   changed from v1, but the functionality remained.
>
> Is this solution sounds good? Do you want me to resend the two patch?

You don't need to resend. I just got back from vacation. I will look
at it tomorrow.

g.

>
> Regards,
> Péter
>
>> Explanantion of the issue (from patch 2):
>> When the kernel is built with CONFIG_PREEMPT it is possible to reach a state
>> when all modules loaded but some driver still stuck in the deferred list
>> and there is a need for external event to kick the deferred queue to probe
>> these drivers.
>>
>> The issue has been observed on embedded systems with CONFIG_PREEMPT enabled,
>> audio support built as modules and using nfsroot for root filesystem.
>>
>> The following log fragment shows such sequence when all audio modules
>> were loaded but the sound card is not present since the machine driver has
>> failed to probe due to missing dependency during it's probe.
>> The board is am335x-evmsk (McASP<->tlv320aic3106 codec) with davinci-evm
>> machine driver:
>>
>> ...
>> [   12.615118] davinci-mcasp 4803c000.mcasp: davinci_mcasp_probe: ENTER
>> [   12.719969] davinci_evm sound.3: davinci_evm_probe: ENTER
>> [   12.725753] davinci_evm sound.3: davinci_evm_probe: snd_soc_register_card
>> [   12.753846] davinci-mcasp 4803c000.mcasp: davinci_mcasp_probe: snd_soc_register_component
>> [   12.922051] davinci-mcasp 4803c000.mcasp: davinci_mcasp_probe: snd_soc_register_component DONE
>> [   12.950839] davinci_evm sound.3: ASoC: platform (null) not registered
>> [   12.957898] davinci_evm sound.3: davinci_evm_probe: snd_soc_register_card DONE (-517)
>> [   13.099026] davinci-mcasp 4803c000.mcasp: Kicking the deferred list
>> [   13.177838] davinci-mcasp 4803c000.mcasp: really_probe: probe_count = 2
>> [   13.194130] davinci_evm sound.3: snd_soc_register_card failed (-517)
>> [   13.346755] davinci_mcasp_driver_init: LEAVE
>> [   13.377446] platform sound.3: Driver davinci_evm requests probe deferral
>> [   13.592527] platform sound.3: really_probe: probe_count = 0
>>
>> In the log the machine driver enters it's probe at 12.719969 (this point it
>> has been removed from the deferred lists). McASP driver already executing
>> it's probing (since 12.615118).
>> The machine driver tries to construct the sound card (12.950839) but did
>> not found one of the components so it fails. After this McASP driver
>> registers all the ASoC components (the machine driver still in it's probe
>> function after it failed to construct the card) and the deferred work is
>> prepared at 13.099026 (note that this time the machine driver is not in the
>> lists so it is not going to be handled when the work is executing).
>> Lastly the machine driver exit from it's probe and the core places it to
>> the deferred list but there will be no other driver going to load and the
>> deferred queue is not going to be kicked again - till we have external event
>> like connecting USB stick, etc.
>>
>> The proposed solution is to try the deferred queue once more when the last
>> driver is asking for deferring and we had drivers loaded while this last
>> driver was probing.
>>
>> This way we can avoid drivers stuck in the deferred queue.
>>
>> Regards,
>> Peter
>> ---
>> Peter Ujfalusi (2):
>>   drivercore: dd: Move driver_deferred_probe_add/del function down in
>>     the code
>>   drivercore: deferral race condition fix
>>
>>  drivers/base/dd.c | 71 +++++++++++++++++++++++++++++++++++++------------------
>>  1 file changed, 48 insertions(+), 23 deletions(-)
>
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