Re: [PATCH] drivers/base: use a worker for sysfs unbind

[Greg Kroah-Hartman]

On Mon, Dec 10, 2018 at 09:46:53AM +0100, Daniel Vetter wrote:
> Drivers might want to remove some sysfs files, which needs the same
> locks and ends up angering lockdep. Relevant snippet of the stack
> trace:
> 
>   kernfs_remove_by_name_ns+0x3b/0x80
>   bus_remove_driver+0x92/0xa0
>   acpi_video_unregister+0x24/0x40
>   i915_driver_unload+0x42/0x130 [i915]
>   i915_pci_remove+0x19/0x30 [i915]
>   pci_device_remove+0x36/0xb0
>   device_release_driver_internal+0x185/0x250
>   unbind_store+0xaf/0x180
>   kernfs_fop_write+0x104/0x190
> 
> I've stumbled over this because some new patches by Ram connect the
> snd-hda-intel unload (where we do use sysfs unbind) with the locking
> chains in the i915 unload code (but without creating a new loop),
> which upset our CI. But the bug is already there and can be easily
> reproduced by unbind i915 directly.

This is odd, why wouldn't any driver hit this issue?  And why now since
you say this is triggerable today?

I know scsi was doing some strange things like trying to remove the
device itself from a sysfs callback on the device, which requires it to
just call a different kobject function created just for that type of
thing.  Would that also make sense to do here instead of your workqueue?

thanks,

greg k-h