Re: [PATCH 12/21] driver core: bus: bus iterator cleanups

Geert Uytterhoeven
2023-02-21T12:54:49Z

Hi Greg,

On Wed, Feb 8, 2023 at 12:15 PM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
> Convert the bus_for_each_dev(), bus_find_device, and bus_for_each_drv()
> functions to use bus_to_subsys() and not use the back-pointer to the
> private structure.
>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Thanks for your patch, which is now commit 83b9148df2c95e23 ("driver
core: bus: bus iterator cleanups") in driver-core-next.

I have bisected an early kernel crash on the Renesas Salvator-XS
board to this commit:

Unable to handle kernel NULL pointer dereference at virtual
address 0000000000000028
...
Call trace:
__lock_acquire+0x530/0x20f0
lock_acquire.part.0+0xc8/0x210
lock_acquire+0x64/0x80
_raw_spin_lock+0x4c/0x60
bus_to_subsys+0x24/0xac
bus_for_each_dev+0x30/0xcc
soc_device_match+0x4c/0xe0
r8a7795_sysc_init+0x18/0x60
rcar_sysc_pd_init+0xb0/0x33c
do_one_initcall+0x128/0x2bc

> --- a/drivers/base/bus.c
> +++ b/drivers/base/bus.c
> @@ -355,18 +355,20 @@ static struct device *next_device(struct klist_iter *i)
> int bus_for_each_dev(const struct bus_type *bus, struct device *start,
> void *data, int (*fn)(struct device *, void *))
> {
> + struct subsys_private *sp = bus_to_subsys(bus);

If bus_to_subsys() is called from an early_initcall(), bus_kset is
still NULL, causing a crash.

> struct klist_iter i;
> struct device *dev;
> int error = 0;
>
> - if (!bus || !bus->p)

Before, the !bus->sp check prevented the crash...

> + if (!sp)
> return -EINVAL;

... and instructed soc_device_match() to go into
early_soc_dev_attr mode.

I have sent a fix
"[PATCH] driver core: bus: Handle early calls to bus_to_subsys()"
https://lore.kernel.org/r/0a92979f6e790737544638e8a4c19b0564e660a2.1676983596.git.geert+renesas@glider.be

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds