Messages in this thread | | | From | Saravana Kannan <> | Date | Tue, 9 Jun 2020 00:30:04 -0700 | Subject | Re: [PATCH v3] driver core: Break infinite loop when deferred probe can't be satisfied |
| |
On Mon, Jun 8, 2020 at 11:45 PM Marco Felsch <m.felsch@pengutronix.de> wrote: > > On 20-06-08 13:11, Andrzej Hajda wrote: > > > > On 08.06.2020 11:17, Marco Felsch wrote: > > > On 20-03-26 18:31, Andy Shevchenko wrote: > > >> On Thu, Mar 26, 2020 at 03:01:22PM +0000, Grant Likely wrote: > > >>> On 25/03/2020 12:51, Andy Shevchenko wrote: > > >>>> On Tue, Mar 24, 2020 at 08:29:01PM -0700, Saravana Kannan wrote: > > >>>>> On Tue, Mar 24, 2020 at 5:38 AM Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote: > > >>>>>> Consider the following scenario. > > >>>>>> > > >>>>>> The main driver of USB OTG controller (dwc3-pci), which has the following > > >>>>>> functional dependencies on certain platform: > > >>>>>> - ULPI (tusb1210) > > >>>>>> - extcon (tested with extcon-intel-mrfld) > > >>>>>> > > >>>>>> Note, that first driver, tusb1210, is available at the moment of > > >>>>>> dwc3-pci probing, while extcon-intel-mrfld is built as a module and > > >>>>>> won't appear till user space does something about it. > > >>>>>> > > >>>>>> This is depicted by kernel configuration excerpt: > > >>>>>> > > >>>>>> CONFIG_PHY_TUSB1210=y > > >>>>>> CONFIG_USB_DWC3=y > > >>>>>> CONFIG_USB_DWC3_ULPI=y > > >>>>>> CONFIG_USB_DWC3_DUAL_ROLE=y > > >>>>>> CONFIG_USB_DWC3_PCI=y > > >>>>>> CONFIG_EXTCON_INTEL_MRFLD=m > > >>>>>> > > >>>>>> In the Buildroot environment the modules are probed by alphabetical ordering > > >>>>>> of their modaliases. The latter comes to the case when USB OTG driver will be > > >>>>>> probed first followed by extcon one. > > >>>>>> > > >>>>>> So, if the platform anticipates extcon device to be appeared, in the above case > > >>>>>> we will get deferred probe of USB OTG, because of ordering. > > >>>>>> > > >>>>>> Since current implementation, done by the commit 58b116bce136 ("drivercore: > > >>>>>> deferral race condition fix") counts the amount of triggered deferred probe, > > >>>>>> we never advance the situation -- the change makes it to be an infinite loop. > > >>>>> Hi Andy, > > >>>>> > > >>>>> I'm trying to understand this sequence of steps. Sorry if the questions > > >>>>> are stupid -- I'm not very familiar with USB/PCI stuff. > > >>>> Thank you for looking into this. My answer below. > > >>>> > > >>>> As a first thing I would like to tell that there is another example of bad > > >>>> behaviour of deferred probe with no relation to USB. The proposed change also > > >>>> fixes that one (however, less possible to find in real life). > > >>>> > > >>>>>> ---8<---8<--- > > >>>>>> > > >>>>>> [ 22.187127] driver_deferred_probe_trigger <<< 1 > > >>>>>> > > >>>>>> ...here is the late initcall triggers deferred probe... > > >>>>>> > > >>>>>> [ 22.191725] platform dwc3.0.auto: deferred_probe_work_func in deferred list > > >>>>>> > > >>>>>> ...dwc3.0.auto is the only device in the deferred list... > > >>>>> Ok, dwc3.0.auto is the only unprobed device at this point? > > >>>> Correct. > > >>>> > > >>>>>> [ 22.198727] platform dwc3.0.auto: deferred_probe_work_func 1 <<< counter 1 > > >>>>>> > > >>>>>> ...the counter before mutex is unlocked is kept the same... > > >>>>>> > > >>>>>> [ 22.205663] platform dwc3.0.auto: Retrying from deferred list > > >>>>>> > > >>>>>> ...mutes has been unlocked, we try to re-probe the driver... > > >>>>>> > > >>>>>> [ 22.211487] bus: 'platform': driver_probe_device: matched device dwc3.0.auto with driver dwc3 > > >>>>>> [ 22.220060] bus: 'platform': really_probe: probing driver dwc3 with device dwc3.0.auto > > >>>>>> [ 22.238735] bus: 'ulpi': driver_probe_device: matched device dwc3.0.auto.ulpi with driver tusb1210 > > >>>>>> [ 22.247743] bus: 'ulpi': really_probe: probing driver tusb1210 with device dwc3.0.auto.ulpi > > >>>>>> [ 22.256292] driver: 'tusb1210': driver_bound: bound to device 'dwc3.0.auto.ulpi' > > >>>>>> [ 22.263723] driver_deferred_probe_trigger <<< 2 > > >>>>>> > > >>>>>> ...the dwc3.0.auto probes ULPI, we got successful bound and bumped counter... > > >>>>>> > > >>>>>> [ 22.268304] bus: 'ulpi': really_probe: bound device dwc3.0.auto.ulpi to driver tusb1210 > > >>>>> So where did this dwc3.0.auto.ulpi come from? > > >>>>> Looks like the device is created by dwc3_probe() through this call flow: > > >>>>> dwc3_probe() -> dwc3_core_init() -> dwc3_core_ulpi_init() -> > > >>>>> dwc3_ulpi_init() -> ulpi_register_interface() -> ulpi_register() > > >>>> Correct. > > >>>> > > >>>>>> [ 22.276697] platform dwc3.0.auto: Driver dwc3 requests probe deferral > > >>>>> Can you please point me to which code patch actually caused the probe > > >>>>> deferral? > > >>>> Sure, it's in drd.c. > > >>>> > > >>>> if (device_property_read_string(dev, "linux,extcon-name", &name) == 0) { > > >>>> edev = extcon_get_extcon_dev(name); > > >>>> if (!edev) > > >>>> return ERR_PTR(-EPROBE_DEFER); > > >>>> return edev; > > >>>> } > > >>>> > > >>>>>> ...but extcon driver is still missing... > > >>>>>> > > >>>>>> [ 22.283174] platform dwc3.0.auto: Added to deferred list > > >>>>>> [ 22.288513] platform dwc3.0.auto: driver_deferred_probe_add_trigger local counter: 1 new counter 2 > > >>>>> I'm not fully aware of all the USB implications, but if extcon is > > >>>>> needed, why can't that check be done before we add and probe the ulpi > > >>>>> device? That'll avoid this whole "fake" probing and avoid the counter > > >>>>> increase. And avoid the need for this patch that's touching the code > > >>>>> code that's already a bit delicate. > > >>>>> Also, with my limited experience with all the possible drivers in the > > >>>>> kernel, it's weird that the ulpi device is added and probed before we > > >>>>> make sure the parent device (dwc3.0.auto) can actually probe > > >>>>> successfully. > > >>>> As I said above the deferred probe trigger has flaw on its own. > > >>>> Even if we fix for USB case, there is (and probably will be) others. > > >>> Right here is the driver design bug. A driver's probe() hook should *not* > > >>> return -EPROBE_DEFER after already creating child devices which may have > > >>> already been probed. > > >> Any documentation statement for this requirement? > > >> > > >> By the way, I may imagine other mechanisms that probe the driver on other CPU > > >> at the same time (let's consider parallel modprobes). The current code has a > > >> flaw with that. > > > Hi, > > > > > > sorry for picking this up again but I stumbled above the same issue > > > within the driver imx/drm driver which is using the component framework. > > > I end up in a infinity boot loop if I enabled the HDMI (which is the > > > DesignWare bridge device) and the LVDS support and the LVDS bind return > > > with EPROBE_DEFER. There are no words within the component framework docs > > > which says that this is forbidden. Of course we can work-around the > > > driver-core framework but IMHO this shouldn't be the way to go. I do not > > > say that we should revert the commit introducing the regression but we > > > should address this not only by extending the docs since the most > > > drm-drivers are using the component framework and can end up in the same > > > situation. > > > > I am not sure why do you think this is similar issue. > > Because I see trying to bind the device over and over.. > > > Please describe the issue in more detail. Which drivers defers probe and > > why, and why do you have infinite loop. > > As said I'm currently on the imx-drm driver. The iMX6 devices are > using the synopsis HDMI IP core and so they are using this bridge device > driver (drivers/gpu/drm/bridge/synopsys/). The imx-drm driver can be > build module wise. As example I enabled the LDB and the HDMI support. > The HDMI driver is composed as platform driver with different > (sub-)drivers and devices. Those devices are populated by the HDMI core > driver _probe() function and triggers a driver_deferred_probe_trigger() > after the driver successfully probed. The LDB driver bind() returns > -EPROBE_DEFER because the panel we are looking for depends on a defered > regulator device. Now the defered probe code tries to probe the defered > devices again because the local-trigger count was changed by the HDMI > driver and we are in the never ending loop. > > > In general deferring probe from bind is not forbidden, but it should be > > used carefully (as everything in kernel :) ). Fixing deferring probe > > issues in many cases it is a matter of figuring out 'dependency loops' > > and breaking them by splitting device initialization into more than one > > phase. > > We are on the way of splitting the imx-drm driver but there are many > other DRM drivers using the component framework. As far as I can see the > sunxi8 driver is component based and uses the same HDMI driver. I'm with > Andy that we should fix that on the common/core place.
I'm not opposed to fixing this at the common/core level if that's possible, but Andy's patch still has a bug where it might never probe a device. I still haven't seen an answer to this. https://lore.kernel.org/lkml/CAGETcx_3+YH_LmNUCAAk1OaXk6noHEXxcE+ckkoBqKJJhtpDjQ@mail.gmail.com/
-Saravana
| |