Re: [PATCH] driver core: bus: Handle early calls to bus_to_subsys() - Greg Kroah-Hartman

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: "Rafael J . Wysocki" <rafael@kernel.org>,
	Arnd Bergmann <arnd@arndb.de>, Lee Jones <lee@kernel.org>,
	linux-kernel@vger.kernel.org, linux-renesas-soc@vger.kernel.org
Subject: Re: [PATCH] driver core: bus: Handle early calls to bus_to_subsys()
Date: Tue, 21 Feb 2023 14:47:49 +0100	[thread overview]
Message-ID: <Y/TLhUewwDJ+RGXd@kroah.com> (raw)
In-Reply-To: <0a92979f6e790737544638e8a4c19b0564e660a2.1676983596.git.geert+renesas@glider.be>

On Tue, Feb 21, 2023 at 01:53:51PM +0100, Geert Uytterhoeven wrote:
> When calling soc_device_match() from early_initcall(), bus_kset is still
> NULL, causing a crash:
> 
>     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
> 
> Before, bus_for_each_dev() handled this gracefully by checking that
> the back-pointer to the private structure was valid.
> 
> Fix this by adding a NULL check for bus_kset to bus_to_subsys().
> 
> Fixes: 83b9148df2c95e23 ("driver core: bus: bus iterator cleanups")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
>  drivers/base/bus.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/base/bus.c b/drivers/base/bus.c
> index cfe8615d5106f030..dd4b82d7510f68fb 100644
> --- a/drivers/base/bus.c
> +++ b/drivers/base/bus.c
> @@ -62,7 +62,7 @@ static struct subsys_private *bus_to_subsys(const struct bus_type *bus)
>  	struct subsys_private *sp = NULL;
>  	struct kobject *kobj;
>  
> -	if (!bus)
> +	if (!bus || !bus_kset)
>  		return NULL;
>  
>  	spin_lock(&bus_kset->list_lock);

Thanks for this, I'll queue it up after my patches get sent to Linus.

greg k-h