linux-kernel - Re: [PATCH] nvdimm: nvdimm_bus_register: Avoid adding device to the unregistered bus

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Date:   Thu, 16 Mar 2023 22:59:51 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     "lizhijian@...itsu.com" <lizhijian@...itsu.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "vishal.l.verma@...el.com" <vishal.l.verma@...el.com>,
        "dave.jiang@...el.com" <dave.jiang@...el.com>,
        "ira.weiny@...el.com" <ira.weiny@...el.com>,
        "nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] nvdimm: nvdimm_bus_register: Avoid adding device to the
 unregistered bus

lizhijian@...itsu.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!

That's expected though, you can't block libnvdimm_init and then expect
modules that link to libnvdimm to work. You would also need to block all
modules / initcalls that depend on libnvdimm_init having run. I'll
respond to the other thread with some ideas.