On 7/19/2021 3:22 PM, Andy Shevchenko wrote: > On Mon, Jul 19, 2021 at 03:00:17PM +0300, Laurentiu Tudor wrote: >> On 7/16/2021 8:21 PM, Jon Nettleton wrote: >>> On Fri, Jul 16, 2021 at 2:17 PM Andy Shevchenko >>> <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote: >>>> >>>> On Fri, Jul 16, 2021 at 01:16:02PM +0300, laurentiu.tudor@xxxxxxx wrote: >>>>> From: Laurentiu Tudor <laurentiu.tudor@xxxxxxx> >>>>> >>>>> software_node_notify(), on KOBJ_REMOVE drops the refcount twice on managed >>>>> software nodes, thus leading to underflow errors. Balance the refcount by >>>>> bumping it in the device_create_managed_software_node() function. >>>>> >>>>> The error [1] was encountered after adding a .shutdown() op to our >>>>> fsl-mc-bus driver. >>>> >>>> Looking into the history of adding ->shutdown() to dwc3 driver (it got reverted >>>> later on), I can tell that probably something is wrong in the ->shutdown() >>>> method itself. >>> >>> Isn't the other alternative to just remove the second kobject_put from >>> KOBJ_REMOVE ? >>> >> >> Or maybe on top of Heikki's suggestion, replace the calls to >> sysfs_create_link() from KOBJ_ADD with sysfs_create_link_nowarn()? > > _noearn will hide the problem. It was there, it was removed from there. > Perhaps we have to understand the root cause better (some specific flow?). > > Any insight from you on the flow when the issue appears? I.o.w. what happened > on the big picture that we got into the warning you see? > I encountered the initial issue when trying to shut down a system booted with ACPI but only after adding a .shutdown() callback to our bus driver so that the devices are properly taken down. The problem was that software_node_notify(), on KOBJ_REMOVE was dropping the reference count twice leading to an underflow error. My initial proposal was to just bump the refcount in device_create_managed_software_node(). The device properties that triggered the problem are created here [1]. Heikko suggested that instead of manually incrementing the refcount to use software_node_notify(KOBJ_ADD). This triggered the second issue, a duplicated sysfs entry warning originating in the usb subsystem: device_create_managed_software_node() ends up being called twice, once here [2] and secondly, the place I previous mentioned [1]. [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/acpi/arm64/iort.c#n952 [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/usb/dwc3/host.c#n111 --- Best Regards, Laurentiu
