linux-kernel - Re: [PATCH] md/raid10: Use struct

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Message-ID: <CAPhsuW5CmfTm4Eu6AXgA669Obf3Sefj51v18-w=wL7d1bTz5tA@mail.gmail.com>
Date:   Mon, 7 Jan 2019 15:01:37 -0800
From:   Song Liu <liu.song.a23@...il.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Shaohua Li <shli@...nel.org>, linux-raid@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] md/raid10: Use struct_size() in kmalloc()

On Fri, Jan 4, 2019 at 1:14 PM Gustavo A. R. Silva
<gustavo@...eddedor.com> wrote:
>
> One of the more common cases of allocation size calculations is finding
> the size of a structure that has a zero-sized array at the end, along
> with memory for some number of elements for that array. For example:
>
> struct foo {
>     int stuff;
>     void *entry[];
> };
>
> instance = kmalloc(sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);
>
> Instead of leaving these open-coded and prone to type mistakes, we can
> now use the new struct_size() helper:
>
> instance = kmalloc(struct_size(instance, entry, count), GFP_KERNEL);
>
> This code was detected with the help of Coccinelle.
>
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>

Acked-by: Song Liu <songliubraving@...com>

> ---
>  drivers/md/raid10.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index abb5d382f64d..320cb430cca6 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -4788,8 +4788,7 @@ static int handle_reshape_read_error(struct mddev *mddev,
>         int idx = 0;
>         struct page **pages;
>
> -       r10b = kmalloc(sizeof(*r10b) +
> -              sizeof(struct r10dev) * conf->copies, GFP_NOIO);
> +       r10b = kmalloc(struct_size(r10b, devs, conf->copies), GFP_NOIO);
>         if (!r10b) {
>                 set_bit(MD_RECOVERY_INTR, &mddev->recovery);
>                 return -ENOMEM;
> --
> 2.20.1
>