RE: [PATCH] nvdimm: nvdimm_bus_register: Avoid adding device to the unregistered bus

[Dan Williams]

Li Zhijian wrote:
> nvdimm_bus_register() could be called from other modules, such as nfit,
> but it can only be called after the nvdimm_bus_type is registered.
> 
>  BUG: kernel NULL pointer dereference, address: 0000000000000098
>  #PF: supervisor read access in kernel mode
>  #PF: error_code(0x0000) - not-present page
>  PGD 0 P4D 0
>  Oops: 0000 [#1] PREEMPT SMP PTI
>  CPU: 0 PID: 117 Comm: systemd-udevd Not tainted 6.2.0-rc6-pmem+ #97
>  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
>  RIP: 0010:bus_add_device+0x58/0x150
>  Call Trace:
>   <TASK>
>   device_add+0x3ac/0x980
>   nvdimm_bus_register+0x16d/0x1d0
>   acpi_nfit_init+0xb72/0x1f90 [nfit]
>   acpi_nfit_add+0x1d5/0x200 [nfit]
>   acpi_device_probe+0x45/0x160

Can you explain a bit more how to hit this crash? This has not been a
problem historically and the explanation above makes it sound like this
is a theoretical issue.

libnvdimm_init() *should* be done before the nfit driver can attempt
nvdimm_bus_register(). So, something else is broken if
nvdimm_bus_register() can be called before libnvdimm_init(), or after
libnvdimm_exit().