Re: [PATCH] lib/kobject: Simplify checking of parameters in kobj_ns_type_register.

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, Jun 17, 2022 at 04:38:32PM +0800, wuchi wrote:
> 1. Merge checking of following code:
>     if (type >= KOBJ_NS_TYPES)
>     ...
>     if (type <= KOBJ_NS_TYPE_NONE)

Why?

> 2. Move the checking of parameters out of critical section, there is
> no need to check that with spinlock.

Why does it matter?


> 
> Signed-off-by: wuchi <wuchi.zero@gmail.com>
> ---
>  lib/kobject.c | 14 ++++----------
>  1 file changed, 4 insertions(+), 10 deletions(-)
> 
> diff --git a/lib/kobject.c b/lib/kobject.c
> index 5f0e71ab292c..6a8b009682b8 100644
> --- a/lib/kobject.c
> +++ b/lib/kobject.c
> @@ -996,19 +996,13 @@ static const struct kobj_ns_type_operations *kobj_ns_ops_tbl[KOBJ_NS_TYPES];
>  int kobj_ns_type_register(const struct kobj_ns_type_operations *ops)
>  {
>  	enum kobj_ns_type type = ops->type;
> -	int error;
> -
> -	spin_lock(&kobj_ns_type_lock);
> +	int error = -EBUSY;
>  
> -	error = -EINVAL;
> -	if (type >= KOBJ_NS_TYPES)
> -		goto out;
> +	if (unlikely(type >= KOBJ_NS_TYPES || type <= KOBJ_NS_TYPE_NONE))

Why add unlikely?  Did you measure the performance benifit?  If not,
please never add likely/unlikely.

> +		return -EINVAL;
>  
> -	error = -EINVAL;
> -	if (type <= KOBJ_NS_TYPE_NONE)
> -		goto out;
> +	spin_lock(&kobj_ns_type_lock);
>  
> -	error = -EBUSY;


How did you test this?  What is the benefit?

thanks,

greg k-h