On Tue, Jul 20, 2021 at 12:22 PM Laurentiu Tudor <laurentiu.tudor@xxxxxxx> wrote: > 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]. This [3] is what I have reported against DWC3 when ->shutdown() has been added there. And here [4] is another thread about the issue with that callback. The ->release() callback is called at put_device() [5] and ->shutdown() is called before that [6]. That said, can you inspect your ->shutdown() implementation once more time and perhaps see if there is anything that can be amended? > [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 [3]: https://lore.kernel.org/linux-usb/CAHp75Vd-5U5zgtDfM5C3Jsx51HVYB+rNcHYC2XP=G7dOd=cdTg@xxxxxxxxxxxxxx/ [4]: https://lore.kernel.org/linux-usb/c3c75895-313a-5be7-6421-b32bac741a88@xxxxxxx/T/#u [5]: https://elixir.bootlin.com/linux/latest/source/drivers/base/core.c#L2216 [6]: https://elixir.bootlin.com/linux/latest/source/drivers/base/core.c#L4447 -- With Best Regards, Andy Shevchenko
