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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(-) > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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