linux-kernel - Re: [PATCH] driver core: bus: Mark an impossible error path with WARN_ON() in bus_add

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Message-ID: <2024091530-antacid-magical-8302@gregkh>
Date: Sun, 15 Sep 2024 15:00:27 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Zijun Hu <zijun_hu@...oud.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, linux-kernel@...r.kernel.org,
	Zijun Hu <quic_zijuhu@...cinc.com>
Subject: Re: [PATCH] driver core: bus: Mark an impossible error path with
 WARN_ON() in bus_add_driver()

On Sun, Sep 15, 2024 at 06:22:05PM +0800, Zijun Hu wrote:
> From: Zijun Hu <quic_zijuhu@...cinc.com>
> 
> driver_attach() called by bus_add_driver() always returns 0, so its
> corresponding error path will never happen, hence mark the impossible
> error path with WARN_ON() to remind readers to disregard it.

So you just caused the machine to crash and reboot if that happens
(remember, panic-on-warn is enabled in a few billion Linux systems...)

> Signed-off-by: Zijun Hu <quic_zijuhu@...cinc.com>
> ---
>  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 657c93c38b0d..59a48edda267 100644
> --- a/drivers/base/bus.c
> +++ b/drivers/base/bus.c
> @@ -673,7 +673,7 @@ int bus_add_driver(struct device_driver *drv)
>  	klist_add_tail(&priv->knode_bus, &sp->klist_drivers);
>  	if (sp->drivers_autoprobe) {
>  		error = driver_attach(drv);
> -		if (error)
> +		if (WARN_ON(error))

What exactly are you trying to show here?  If this really can never
fail, then let's just remove the check entirely.

thanks,

greg k-h