Re: [PATCH v3 06/11] mm/util: Deduplicate code in {kstrdup,kstrndup,kmemdup_nul}

[Simon Horman <horms@kernel.org>]

On Fri, Jun 21, 2024 at 10:29:54AM +0800, Yafang Shao wrote:
> These three functions follow the same pattern. To deduplicate the code,
> let's introduce a common help __kstrndup().
> 
> Suggested-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>

Hi Yafang Shao,

Some minor nits from my side.

> ---
>  mm/internal.h | 24 ++++++++++++++++++++++++
>  mm/util.c     | 27 ++++-----------------------
>  2 files changed, 28 insertions(+), 23 deletions(-)
> 
> diff --git a/mm/internal.h b/mm/internal.h
> index b2c75b12014e..fd87f685739b 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -1521,4 +1521,28 @@ static inline void shrinker_debugfs_remove(struct dentry *debugfs_entry,
>  void workingset_update_node(struct xa_node *node);
>  extern struct list_lru shadow_nodes;
>  
> +/**
> + * __kstrndup - Create a NUL-terminated string from @s, which might be unterminated.
> + * @s: The data to stringify
> + * @len: The size of the data, including the null terminator
> + * @gfp: the GFP mask used in the kmalloc() call when allocating memory
> + *
> + * Return: newly allocated copy of @s with NUL-termination or %NULL in
> + * case of error
> + */
> +static __always_inline char *__kstrndup(const char *s, size_t len, gfp_t gfp)
> +{
> +	char *buf;
> +
> +	buf = kmalloc_track_caller(len, gfp);
> +	if (!buf)
> +		return NULL;
> +
> +	memcpy(buf, s, len);
> +	/* Ensure the buf is always NUL-terminated, regardless of @s. */
> +	buf[len - 1] = '\0';
> +	return buf;
> +}
> +
> +

nit: One blank line is enough.

>  #endif	/* __MM_INTERNAL_H */
> diff --git a/mm/util.c b/mm/util.c
> index 41c7875572ed..d9135c5fdf7f 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -58,17 +58,8 @@ char *kstrdup(const char *s, gfp_t gfp)
>  	if (!s)
>  		return NULL;
>  
> -	len = strlen(s) + 1;
> -	buf = kmalloc_track_caller(len, gfp);
> -	if (buf) {
> -		memcpy(buf, s, len);
> -		/* During memcpy(), the string might be updated to a new value,
> -		 * which could be longer than the string when strlen() is
> -		 * called. Therefore, we need to add a null termimator.
> -		 */
> -		buf[len - 1] = '\0';
> -	}
> -	return buf;

nit: The local variable buf is now unused, and should be removed from kstrdup().
     Likewise for kstrndup() and kmemdup_nul()

     Flagged by W=1 builds with gcc-13 and clang-18, and Smatch.

> +	len = strlen(s);
> +	return __kstrndup(s, len + 1, gfp);
>  }
>  EXPORT_SYMBOL(kstrdup);
>  
> @@ -111,12 +102,7 @@ char *kstrndup(const char *s, size_t max, gfp_t gfp)
>  		return NULL;
>  
>  	len = strnlen(s, max);
> -	buf = kmalloc_track_caller(len+1, gfp);
> -	if (buf) {
> -		memcpy(buf, s, len);
> -		buf[len] = '\0';
> -	}
> -	return buf;
> +	return __kstrndup(s, len + 1, gfp);
>  }
>  EXPORT_SYMBOL(kstrndup);
>  
> @@ -195,12 +181,7 @@ char *kmemdup_nul(const char *s, size_t len, gfp_t gfp)
>  	if (!s)
>  		return NULL;
>  
> -	buf = kmalloc_track_caller(len + 1, gfp);
> -	if (buf) {
> -		memcpy(buf, s, len);
> -		buf[len] = '\0';
> -	}
> -	return buf;
> +	return __kstrndup(s, len + 1, gfp);
>  }
>  EXPORT_SYMBOL(kmemdup_nul);
>  
> -- 
> 2.39.1
> 
>