linux-kernel - Re: [PATCH 3/3] driver core: class: Delete a redundant check in APIs class_(for_each|find)

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Message-ID: <2824dfcd-0f8d-4d5e-a687-9b0398ba1458@icloud.com>
Date: Tue, 12 Nov 2024 22:51:35 +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 3/3] driver core: class: Delete a redundant check in APIs
 class_(for_each|find)_device()

On 2024/11/12 19:45, Greg Kroah-Hartman wrote:
> On Tue, Nov 05, 2024 at 08:20:24AM +0800, Zijun Hu wrote:
>> From: Zijun Hu <quic_zijuhu@...cinc.com>
>>
>> Delete redundant check (!@...ss) in both API class_for_each_device() and
>> class_find_device() with below reasons:
>>
>> - The check is covered by later check (!@sp).
>> - Callers are unlikely to call both APIs with NULL class argument.
>> - Make parameter check consistent with all of other class APIs.
>>
>> Signed-off-by: Zijun Hu <quic_zijuhu@...cinc.com>
>> ---
>>  drivers/base/class.c | 4 ----
>>  1 file changed, 4 deletions(-)
>>
>> diff --git a/drivers/base/class.c b/drivers/base/class.c
>> index e81da280af74..120d3aeb52fe 100644
>> --- a/drivers/base/class.c
>> +++ b/drivers/base/class.c
>> @@ -408,8 +408,6 @@ int class_for_each_device(const struct class *class, const struct device *start,
>>  	struct device *dev;
>>  	int error = 0;
>>  
>> -	if (!class)
>> -		return -EINVAL;
>>  	if (!sp) {
>>  		WARN(1, "%s called for class '%s' before it was registered",
>>  		     __func__, class->name);
> 
> Now, if I pass in NULL for class, I get an odd warning, AND the kernel
> crashes with the dereference of class->name.
> 

yes. you are right.

i did not notice "class->name" in warning message.

> So this is not ok :(
> 
>> @@ -456,8 +454,6 @@ struct device *class_find_device(const struct class *class, const struct device
>>  	struct class_dev_iter iter;
>>  	struct device *dev;
>>  
>> -	if (!class)
>> -		return NULL;
>>  	if (!sp) {
>>  		WARN(1, "%s called for class '%s' before it was registered",
>>  		     __func__, class->name);
> 
> Same here, this change is going to break things if people get it wrong,
> please leave both of these as-is.
> 

okay. agree with you.

> thanks,
> 
> greg k-h