Re: [PATCH v4 1/4] kernel: param: initialize module_kset before do_initcalls()

[Shashank Balaji <shashank.mahadasyam@sony.com>]

On Tue, May 12, 2026 at 05:44:40PM +0530, Sumit Gupta wrote:
> 
> On 12/05/26 14:25, Jon Hunter wrote:
> > Hi Shashank,
> > 
> > On 12/05/2026 03:12, Shashank Balaji wrote:
> > 
> > ...
> > 
> > > > Hi Thierry and Jonathan,
> > > > 
> > > > You can find the context for this email in this patch:
> > > > https://lore.kernel.org/all/20260427-acpi_mod_name-v4-1-22b42240c9bf@sony.com/
> > > > 
> > > > 
> > > > TL;DR: tegra194_cbb_driver and tegra234_cbb_driver are the only drivers
> > > > registering themselves as early as in a pure_initcall. This is a
> > > > problem
> > > > on two fronts:
> > > > 1. Philosophical: As Gary pointed out, pure_initcalls are
> > > > intended to purely
> > > > initialize variables that couldn't be statically initialized. But these
> > > > are doing driver registrations.
> > > > 2. module_kset not initialized at pure_initcall stage: This is
> > > > needed to
> > > > set the module sysfs symlink. Since module_kset is not alive yet during
> > > > pure_initcalls, registering these drivers panics the kernel.
> > 
> > Where exactly is this panic seen? Ie. why are we not seeing this?

The panic happens as a result of this patch series. This series aims to
set .mod_name of struct device_driver for platform drivers. So that, for
built-in drivers, their module sysfs symlink can be created on the basis
of .modname. We essentially want to link a platform driver to its
module. This happens naturally if the driver is built as a loadable
module, but for this to happen for built-in modules, .mod_name needs to be set.

To go from .mod_name to the module sysfs symlink, the module_kset kset
needs to be initialized. This currently happens in a subsys_initcall.
These tegra cbb drivers register themselves in a pure_initcall, i.e.
before subsys_initcall, leading to a null dereference of module_kset.

To fix this, we want to move the module_kset creation to pure_initcall,
and tegra cbb driver registration to core_initcall, so after
pure_initcall.

> > > > We would like to do the tegra cbb driver registration in a
> > > > core_initcall
> > > > (or some later initcall works too), and move module_kset initialization
> > > > to a pure_initcall. Like this:
> > > > 
> > > > diff --git a/drivers/soc/tegra/cbb/tegra194-cbb.c
> > > > b/drivers/soc/tegra/cbb/tegra194-cbb.c
> > > > index ab75d50cc85c..2f69e104c838 100644
> > > > --- a/drivers/soc/tegra/cbb/tegra194-cbb.c
> > > > +++ b/drivers/soc/tegra/cbb/tegra194-cbb.c
> > > > @@ -2342,7 +2342,7 @@ static int __init tegra194_cbb_init(void)
> > > >   {
> > > >          return platform_driver_register(&tegra194_cbb_driver);
> > > >   }
> > > > -pure_initcall(tegra194_cbb_init);
> > > > +core_initcall(tegra194_cbb_init);
> > > > 
> > > >   static void __exit tegra194_cbb_exit(void)
> > > >   {
> > > > diff --git a/drivers/soc/tegra/cbb/tegra234-cbb.c
> > > > b/drivers/soc/tegra/cbb/tegra234-cbb.c
> > > > index fb26f085f691..785072fa4e85 100644
> > > > --- a/drivers/soc/tegra/cbb/tegra234-cbb.c
> > > > +++ b/drivers/soc/tegra/cbb/tegra234-cbb.c
> > > > @@ -1774,7 +1774,7 @@ static int __init tegra234_cbb_init(void)
> > > >   {
> > > >          return platform_driver_register(&tegra234_cbb_driver);
> > > >   }
> > > > -pure_initcall(tegra234_cbb_init);
> > > > +core_initcall(tegra234_cbb_init);
> > > > 
> > > >   static void __exit tegra234_cbb_exit(void)
> > > >   {
> > > > 
> > > > Would this work?
> > 
> > 
> > I am adding Sumit who has been doing a lot of the Tegra CBB driver work.
> > 
> > Sumit, any concerns here? We could run this change through our internal
> > testing to confirm.
> > 
> > Jon
> > 
> 
> CBB driver can be switched to core_initcall.
> pure_initcall was originally added so its IRQ handler is registered
> before other Tegra drivers to catch and print any bad MMIO error
> during their probe.
> Looked at the current state of Tegra drivers:
>  - The other early Tegra drivers (PMC, fuse, flowctrl, ARI) all run at
>    early_initcall, before either pure_ or core_initcall.
>  - The only other Tegra core_initcall is tegra-hsp, and link order keeps
>    CBB ahead of it (drivers/soc/ links before drivers/mailbox/).
> 
> Acked-by: Sumit Gupta <sumitg@nvidia.com>

Thanks, Sumit and Jon!