Re: [PATCH] fs: dodge an atomic in putname if ref == 1

[Jens Axboe]

On 3/11/25 12:18 PM, Mateusz Guzik wrote:
> diff --git a/fs/namei.c b/fs/namei.c
> index 06765d320e7e..add90981cfcd 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -275,14 +275,19 @@ EXPORT_SYMBOL(getname_kernel);
>  
>  void putname(struct filename *name)
>  {
> +	int refcnt;
> +
>  	if (IS_ERR_OR_NULL(name))
>  		return;
>  
> -	if (WARN_ON_ONCE(!atomic_read(&name->refcnt)))
> -		return;
> +	refcnt = atomic_read(&name->refcnt);
> +	if (refcnt != 1) {
> +		if (WARN_ON_ONCE(!refcnt))
> +			return;
>  
> -	if (!atomic_dec_and_test(&name->refcnt))
> -		return;
> +		if (!atomic_dec_and_test(&name->refcnt))
> +			return;
> +	}

Looks good to me, I use this trick with bitops too all the time, to
avoid a RMW when possible.

Reviewed-by: Jens Axboe <axboe@xxxxxxxxx>

-- 
Jens Axboe