Hi Thierry, Jonathan,
Just following up on the below, would moving tegra194_cbb_driver and
tegra234_cbb_driver from pure_initcall to core_initcall work for you?
Thanks,
Shashank
On Tue, Apr 28, 2026 at 10:07:41PM +0900, Shashank Balaji wrote:
> Adding Tegra maintainers.
>
> On Tue, Apr 28, 2026 at 12:10:50PM +0100, Gary Guo wrote:
> > On Tue Apr 28, 2026 at 1:37 AM BST, Shashank Balaji wrote:
> > > Hi Gary,
> > >
> > > On Mon, Apr 27, 2026 at 02:29:55PM +0100, Gary Guo wrote:
> > >> On Mon Apr 27, 2026 at 3:41 AM BST, Shashank Balaji wrote:
> > >> > module_kset is initialized in param_sysfs_init(), a subsys_initcall. A
> > >> > number
> > >> > of platform drivers register themselves prior to subsys_initcalls
> > >> > (tegra194_cbb_driver registers in a pure_initcall, for example). With
> > >> > an
> > >> > upcoming patch ("driver core: platform: set mod_name in driver
> > >> > registration")
> > >> > that sets their mod_name in struct device_driver,
> > >> > lookup_or_create_module_kobject()
> > >> > will be called for those drivers, which calls
> > >> > kset_find_obj(module_kset, mod_name).
> > >> > This causes a null deref because module_kset isn't alive yet.
> > >> >
> > >> > Fix this by initializing module_kset in do_basic_setup() before
> > >> > do_initcalls().
> > >> > Modernize the pr_warn while we're at it.
> > >> >
> > >> > Suggested-by: Greg Kroah-Hartman <[email protected]>
> > >> > Suggested-by: Gary Guo <[email protected]>
> > >>
> > >> I didn't suggest this change :)
> > >>
> > >> I suggested `pure_initcall`, which is just a one line change.
> > >
> > > Oops, sorry about the misattribution.
> > >
> > >> diff --git a/kernel/params.c b/kernel/params.c
> > >> index 74d620bc2521..ac088d4b09a9 100644
> > >> --- a/kernel/params.c
> > >> +++ b/kernel/params.c
> > >> @@ -957,7 +957,7 @@ static int __init param_sysfs_init(void)
> > >>
> > >> return 0;
> > >> }
> > >> -subsys_initcall(param_sysfs_init);
> > >> +pure_initcall(param_sysfs_init);
> > >>
> > >> /*
> > >> * param_sysfs_builtin_init - add sysfs version and parameter
> > >>
> > >> pure_initcall is level 0 so it happens before all other init calls. Does
> > >> it not
> > >> work?
> > >
> > > tegra194_cbb_driver registers itself in a pure_initcall too. We wouldn't
> > > want the ordering of its registration and module_kset init to be link
> > > order
> > > dependent.
> >
> > It's the only device driver that does this. And I don't think it's supposed
> > to.
> >
> > >From documentation:
> >
> > > A "pure" initcall has no dependencies on anything else, and purely
> > > initializes variables that couldn't be statically initialized.
> >
> > I understand that given large amount of drivers registering themselves
> > during
> > core/arch_initcall that there might be regressions if all of them are
> > moved, but
> > surely we can demote these two specific tegra driver to
> > core/postcore_initcall?
> > This will still be called earlier than init_machine call which happens
> > during
> > arch_initcall.
> >
> > Looks like the tegra CBB driver is just doing error logging anyway.
>
> That's a good point, Gary. Thanks!
>
> Hi Thierry and Jonathan,
>
> You can find the context for this email in this patch:
> https://lore.kernel.org/all/[email protected]/
>
> 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.
>
> 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?
>
> Thanks,
> Shashank
>
