| Message ID | 1398774909-13649-1-git-send-email-grant.likely@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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 <grant.likely@linaro.org> > Reviewed-by: Peter Ujfalusi <peter.ujfalusi@ti.com> > Tested-by: Peter Ujfalusi <peter.ujfalusi@ti.com> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > Cc: Mark Brown <broonie@kernel.org> > Cc: Stable <stable@vger.kernel.org> # 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 <gregkh@linuxfoundation.org>
On Tue, Apr 29, 2014 at 2:13 PM, Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote: > 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. [...] >> 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 <gregkh@linuxfoundation.org> Thanks Greg I'll give it a few days in linux-next and then ask Linus to pull. g.
diff --git a/drivers/base/dd.c b/drivers/base/dd.c index 8986b9f22781..62ec61e8f84a 100644 --- a/drivers/base/dd.c +++ b/drivers/base/dd.c @@ -52,6 +52,7 @@ static DEFINE_MUTEX(deferred_probe_mutex); static LIST_HEAD(deferred_probe_pending_list); static LIST_HEAD(deferred_probe_active_list); static struct workqueue_struct *deferred_wq; +static atomic_t deferred_trigger_count = ATOMIC_INIT(0); /** * deferred_probe_work_func() - Retry probing devices in the active list. @@ -135,6 +136,17 @@ static bool driver_deferred_probe_enable = false; * This functions moves all devices from the pending list to the active * list and schedules the deferred probe workqueue to process them. It * should be called anytime a driver is successfully bound to a device. + * + * Note, there is a race condition in multi-threaded probe. In the case where + * more than one device is probing at the same time, it is possible for one + * probe to complete successfully while another is about to defer. If the second + * depends on the first, then it will get put on the pending list after the + * trigger event has already occured and will be stuck there. + * + * The atomic 'deferred_trigger_count' is used to determine if a successful + * trigger has occurred in the midst of probing a driver. If the trigger count + * changes in the midst of a probe, then deferred processing should be triggered + * again. */ static void driver_deferred_probe_trigger(void) { @@ -147,6 +159,7 @@ static void driver_deferred_probe_trigger(void) * into the active list so they can be retried by the workqueue */ mutex_lock(&deferred_probe_mutex); + atomic_inc(&deferred_trigger_count); list_splice_tail_init(&deferred_probe_pending_list, &deferred_probe_active_list); mutex_unlock(&deferred_probe_mutex); @@ -265,6 +278,7 @@ static DECLARE_WAIT_QUEUE_HEAD(probe_waitqueue); static int really_probe(struct device *dev, struct device_driver *drv) { int ret = 0; + int local_trigger_count = atomic_read(&deferred_trigger_count); atomic_inc(&probe_count); pr_debug("bus: '%s': %s: probing driver %s with device %s\n", @@ -310,6 +324,9 @@ probe_failed: /* Driver requested deferred probing */ dev_info(dev, "Driver %s requests probe deferral\n", drv->name); driver_deferred_probe_add(dev); + /* Did a trigger occur while probing? Need to re-trigger if yes */ + if (local_trigger_count != atomic_read(&deferred_trigger_count)) + driver_deferred_probe_trigger(); } else if (ret != -ENODEV && ret != -ENXIO) { /* driver matched but the probe failed */ printk(KERN_WARNING