From mboxrd@z Thu Jan 1 00:00:00 1970 From: gregkh@linuxfoundation.org (Greg Kroah-Hartman) Date: Tue, 29 Apr 2014 06:13:32 -0700 Subject: [PATCH v4] drivercore: deferral race condition fix In-Reply-To: <1398774909-13649-1-git-send-email-grant.likely@linaro.org> References: <1398774909-13649-1-git-send-email-grant.likely@linaro.org> Message-ID: <20140429131332.GA7049@kroah.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, Apr 29, 2014 at 01:35:09PM +0100, Grant Likely wrote: > 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. > > v4: New approach; keep track of trigger events instead of nested probing. > > Signed-off-by: Grant Likely > Reviewed-by: Peter Ujfalusi > Tested-by: Peter Ujfalusi > Cc: Greg Kroah-Hartman > Cc: Mark Brown > Cc: Stable # v3.4+ > --- > > Hi Greg, > > This change needs to go into 3.15. I've got this patch in the > devicetree/merge branch of my tree and can ask Linus to pull it directly > if you would like. Sure, that would be fine: Acked-by: Greg Kroah-Hartman