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

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Message-ID: <8620a8a6-9101-4f53-858f-2e09aa310d16@icloud.com>
Date: Sun, 15 Sep 2024 21:38:15 +0800
From: Zijun Hu <zijun_hu@...oud.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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 2024/9/15 21:00, Greg Kroah-Hartman wrote:
> 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...)
> 
are there good way to mark a if condition which is always or mostly
evaluated to false currently without any side effect?

i think this is a generic requirement since readers may not want to
care about things which will never or rarely happen, below link
involves such discussion:
https://lore.kernel.org/all/2024090444-earmark-showpiece-b3dc@gregkh/

>> 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.
> 
what i want to show is that this error patch will never happen here
currently, so readers can disregard it.

let me try to do it after discussion done.

> thanks,
> 
> greg k-h