linux-kernel - Re: [PATCH v2] driver core: bus: Remove an impossible error handling path in bus_add

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Message-ID: <420b202e-e094-4e82-bf77-dd1c62119aa7@icloud.com>
Date: Tue, 17 Sep 2024 14:53:32 +0800
From: Zijun Hu <zijun_hu@...oud.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>
Cc: linux-kernel@...r.kernel.org, Zijun Hu <quic_zijuhu@...cinc.com>
Subject: Re: [PATCH v2] driver core: bus: Remove an impossible error handling
 path in bus_add_driver()

On 2024/9/17 14:49, Zijun Hu wrote:
> From: Zijun Hu <quic_zijuhu@...cinc.com>
> 
> For the following function call chain:
> API driver_register() -> bus_add_driver() -> driver_attach()
> 
> There is an error handling path for driver_attach() returning non-zero
> or failure in bus_add_driver(), remove it with below reasons:
> 
> - It is impossible for driver_attach() to have failure in bus_add_driver()
>   For int driver_attach(const struct device_driver *drv), the only factor
>   which makes it failed is that bus_to_subsys(@drv->bus) is NULL, but
>   the factor has been excluded by bus_add_driver() before calling it.
> 
> - driver_attach() is irrelevant with driver_register(), so the former's
>   result should not also have an impact on the later.
> 
> Signed-off-by: Zijun Hu <quic_zijuhu@...cinc.com>
> ---
> Changes in v2:
> - Remove the error handling path instead of WARN_ON() it.
> - Correct title and commit message
> - Link to v1: https://lore.kernel.org/r/20240915-bus_add_driver_fix-v1-1-ce5cf1f66601@quicinc.com
> ---
>  drivers/base/bus.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/base/bus.c b/drivers/base/bus.c
> index 657c93c38b0d..54ff92aece92 100644
> --- a/drivers/base/bus.c
> +++ b/drivers/base/bus.c
> @@ -674,7 +674,8 @@ int bus_add_driver(struct device_driver *drv)
>  	if (sp->drivers_autoprobe) {
>  		error = driver_attach(drv);
>  		if (error)
> -			goto out_del_list;
> +			pr_warn("%s: failed to attach driver '%s' to bus '%s'\n",
> +				__func__, drv->name, sp->bus->name);

driver_attach() has __must_check attribute and this error may be
inconsequential for driver_register(), so give pr_warn() here

>  	}
>  	error = module_add_driver(drv->owner, drv);
>  	if (error) {
> @@ -708,7 +709,6 @@ int bus_add_driver(struct device_driver *drv)
>  
>  out_detach:
>  	driver_detach(drv);
> -out_del_list:
>  	klist_del(&priv->knode_bus);
>  out_unregister:
>  	kobject_put(&priv->kobj);
> 
> ---
> base-commit: 6a36d828bdef0e02b1e6c12e2160f5b83be6aab5
> change-id: 20240915-bus_add_driver_fix-f54841e6a69a
> 
> Best regards,