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

Simon Horman
2024-06-21T13:51:47Z

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
>
>