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

From: Greg KH
Date: Fri Jun 17 2022 - 04:49:50 EST


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@xxxxxxxxx>
> ---
> 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