Subject: Re: [PATCH v2] powerpc/vio: drop bus_type from parent device

From: Michael Ellerman <[email-masked]>
Date: Thu, 30 Jul 2020 11:28:38 +1000

[ Added Peter & Greg to Cc ]

Thadeu Lima de Souza Cascardo <[email-masked]> writes:
> Commit df44b479654f62b478c18ee4d8bc4e9f897a9844 ("kobject: return error
> code if writing /sys/.../uevent fails") started returning failure when
> writing to /sys/devices/vio/uevent.
>
> This causes an early udevadm trigger to fail. On some installer versions of
> Ubuntu, this will cause init to exit, thus panicing the system very early
> during boot.
>
> Removing the bus_type from the parent device will remove some of the extra
> empty files from /sys/devices/vio/, but will keep the rest of the layout
> for vio devices, keeping them under /sys/devices/vio/.

What exactly does it change?

I'm finding it hard to evaluate if this change is going to cause a
regression somehow.

I'm also not clear on why removing the bus type is correct, apart from
whether it fixes the bug you're seeing.

> It has been tested that uevents for vio devices don't change after this
> fix, they still contain MODALIAS.
>
> Signed-off-by: Thadeu Lima de Souza Cascardo <[email-masked]>
> Fixes: df44b479654f ("kobject: return error code if writing /sys/.../uevent fails")

AFAICS there haven't been any other fixes for that commit. Do we know
why it is only vio that was affected? (possibly because it's a fake bus
to begin with?)

cheers

> diff --git a/arch/powerpc/platforms/pseries/vio.c b/arch/powerpc/platforms/pseries/vio.c
> index 37f1f25ba804..a94dab3972a0 100644
> --- a/arch/powerpc/platforms/pseries/vio.c
> +++ b/arch/powerpc/platforms/pseries/vio.c
> @@ -36,7 +36,6 @@ static struct vio_dev vio_bus_device  = { /* fake "parent" device */
>  	.name = "vio",
>  	.type = "",
>  	.dev.init_name = "vio",
> -	.dev.bus = &vio_bus_type,
>  };
>  
>  #ifdef CONFIG_PPC_SMLPAR
> -- 
> 2.20.1