Re: [PATCH v2] driver core: bus: Remove an impossible error handling path in bus_add_driver()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Sun, Oct 13, 2024 at 11:46:46PM +0800, Zijun Hu wrote:
> On 2024/10/13 23:02, Greg Kroah-Hartman wrote:
> > On Tue, Sep 17, 2024 at 02:53:32PM +0800, Zijun Hu wrote:
> >> On 2024/9/17 14:49, Zijun Hu wrote:
> >>> From: Zijun Hu <quic_zijuhu@quicinc.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@quicinc.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
> > 
> > Yes, but you  now ignore the error, so someone will come back and add
> > that error handling in.  I'd just leave it as-is.
> > 
> 
> driver API driver_attach() may ONLY have below error -EINVAL.
> is it worthy of a __must_check attribute ?

Yes.

> i agree with you to leave it as-is if your answer is "YES".
> otherwise, i would like to also simply remove __must_check attribute.

Please don't.  If you do that, then callers will end up not checking the
results, and we do not want that.

thanks,

greg k-h