On 27/05/16 13:55, Krzysztof Kozlowski wrote: > On 05/27/2016 02:17 PM, Jon Hunter wrote: >> >> On 27/05/16 12:46, Krzysztof Kozlowski wrote: >>> On 05/27/2016 12:28 PM, Jon Hunter wrote: >>>> Hi Krzysztof, >>>> >>>> On 27/05/16 09:37, Krzysztof Kozlowski wrote: >>>> >>>> ... >>>> >>>>> Indeed I was struggling with similar issue in bq27x00_battery. The issue >>>>> was introduced by... me :( when moving the ownership of power supply >>>>> structure from driver to the core. However IMHO my change exposed the >>>>> fundamental problem with power supply. >>>>> >>>>> Anyway a fix for this issue was: >>>>> 7f1a57fdd6cb6e7b (power_supply: Fix possible NULL pointer dereference on >>>>> early uevent) >>>>> AFAIU, this fix no longer fixes all the issues, right? >>>>> >>>>> As for the fundamental problem, the power supply core should not call >>>>> back the driver (get_property()) until the probe ends. Even if the >>>>> di->bat was initialized, some other fields of driver could not be set >>>>> yet. In general, the probe did not end so we should avoid calling driver >>>>> internal functions. >>>> >>>> For my understanding, can you elaborate why the power-supply core should >>>> not call back to the drivers ->get_property() before the probe ends? I >>>> assume that registering the power-supply should be the last thing done >>>> in the probe and so the power-supply should be configured at that point. >>> >>> It is not only about power supply but other resources allocated by the >>> driver. If the power_supply_register() is a last call, then no problem. >>> But if not, then these resources won't be available. >>> >>> Actually I exaggerated a little bit as a fundamental problem as this is >>> quite common pattern. When driver provides something (like power supply) >>> then after registration it should be ready for calls coming from the >>> core or user space. It does not have to be power supply. It might be >>> exposing sysfs entries or file operations (exposed before calling >>> power_supply_register()). >> >> Right, exactly when you register with the power-supply core the device >> better be ready so that handle any incoming calls. > > Yes, the unusual thing here is that the device is called back directly > from the power_supply_register() call. > >> >>>> The problems with the bq27xxx seem to stem from the periodic update of >>>> the bq27xxx status and so it is not clear to me that this is a generic >>>> problem for all power-supply devices. >>> >>> Initially, the generic problem was that the core would call back the >>> driver from power_supply_register() in a synchronous way through >>> power_supply_changed(). The commit 7f1a57fdd6c changed it to an >>> asynchronous call. Here it looks like the same problem - the >>> power_supply_register() calls thermal which calls >>> thermal_zone_device_update() and we are back at the driver... before >>> finishing power_supply_register() call. >> >> So I am still not convinced this is a generic problem but a problem with >> the bq27xxx. In fact, I think that commit 7f1a57fdd6c could be avoided >> if we did something like ... >> >> http://marc.info/?l=linux-kernel&m=146425896332433&w=2 >> >> AFAICT in most cases, in ->get_property() you should have no need to >> access a driver's equivalent of di->bat, because you have already been >> passed a pointer to this via the *psy argument. > > I agree that get_property() shouldn't access di->bat. However if it is > not forbidden (at least by documentation) then someone might just do it > because he does not know about such requirement. In that case, shouldn't the driver should check that di->bat is valid before anyone attempts to dereference it? However, if you and/or Rhyland have a generic fix for preventing this, please go ahead and propose it. Cheers Jon -- nvpublic -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
