Date:   Thu, 16 Mar 2023 19:26:52 -0700
From:   Dan Williams <dan.j.williams@intel.com>
To:     "lizhijian@fujitsu.com" <lizhijian@fujitsu.com>,
        Dan Williams <dan.j.williams@intel.com>,
        "vishal.l.verma@intel.com" <vishal.l.verma@intel.com>,
        "dave.jiang@intel.com" <dave.jiang@intel.com>,
        "ira.weiny@intel.com" <ira.weiny@intel.com>,
        "nvdimm@lists.linux.dev" <nvdimm@lists.linux.dev>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] nvdimm: nvdimm_bus_register: Avoid adding device to the
 unregistered bus
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lizhijian@fujitsu.com wrote:
> 
> 
> On 16/03/2023 23:54, Dan Williams wrote:
> > 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.
> > 
> 
> Dan,
> 
> Configure the kconfig with ACPI_NFIT [=m] && LIBNVDIMM [=y], and add extra kernel booting parameter
> 'initcall_blacklist=libnvdimm_init'. Then kernel panic!
> Theoretically, it will also happen if nvdimm_bus_register() failed.
> 
> 
> For kdump purpose[1], we need to disable libnvdimm driver to ensure metadata in pmem will not be updated again in kdump kernel
> [1]https://lore.kernel.org/linux-mm/3c752fc2-b6a0-2975-ffec-dba3edcf4155@fujitsu.com/T/

Ah, great write up! Let me give that some thought. Apologies for missing
it earlier.

This would have been a good use for:

Link: https://lore.kernel.org/linux-mm/3c752fc2-b6a0-2975-ffec-dba3edcf4155@fujitsu.com

...in the above changelog.