Dan Williams wrote:
> A CONFIG_DEBUG_KOBJECT_RELEASE test of removing a device-dax region
> provider (like modprobe -r dax_hmem) yields:
>
> kobject: 'mapping0' (ffff93eb460e8800): kobject_release, parent
> 0000000000000000 (delayed 2000)
> [..]
> DEBUG_LOCKS_WARN_ON(1)
> WARNING: CPU: 23 PID: 282 at kernel/locking/lockdep.c:232
> __lock_acquire+0x9fc/0x2260
> [..]
> RIP: 0010:__lock_acquire+0x9fc/0x2260
> [..]
> Call Trace:
> <TASK>
> [..]
> lock_acquire+0xd4/0x2c0
> ? ida_free+0x62/0x130
> _raw_spin_lock_irqsave+0x47/0x70
> ? ida_free+0x62/0x130
> ida_free+0x62/0x130
> dax_mapping_release+0x1f/0x30
> device_release+0x36/0x90
> kobject_delayed_cleanup+0x46/0x150
>
> Due to attempting ida_free() on an ida object that has already been
> freed. Devices typically only hold a reference on their parent while
> registered. If a child needs a parent object to complete its release it
> needs to hold a reference that it drops from its release callback.
> Arrange for a dax_mapping to pin its parent dev_dax instance until
> dax_mapping_release().
>
> Fixes: 0b07ce872a9e ("device-dax: introduce 'mapping' devices")
Reviewed-by: Ira Weiny <[email protected]>
