linux-kernel - Re: [PATCH] Staging: rtl8821ae: use kmalloc instead of variable length stack arrays

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Date:	Tue, 10 Jun 2014 11:26:55 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Remi Pommarel <repk@...plefau.lt>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Staging: rtl8821ae: use kmalloc instead of variable
 length stack arrays

On Wed, Jun 04, 2014 at 07:45:45PM +0200, Remi Pommarel wrote:
> This removes stack arrays of variable length and use kmalloc() instead, thus
> removing the sparse warnings "Variable length array is used".
> 
> Signed-off-by: Remi Pommarel <repk@...plefau.lt>
> ---
>  drivers/staging/rtl8821ae/efuse.c | 38 +++++++++++++++++++++++++++++++-------
>  1 file changed, 31 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/staging/rtl8821ae/efuse.c b/drivers/staging/rtl8821ae/efuse.c
> index 206012c..a41aa84 100644
> --- a/drivers/staging/rtl8821ae/efuse.c
> +++ b/drivers/staging/rtl8821ae/efuse.c
> @@ -232,7 +232,7 @@ void read_efuse(struct ieee80211_hw *hw, u16 _offset, u16 _size_byte, u8 *pbuf)
>  {
>  	struct rtl_priv *rtlpriv = rtl_priv(hw);
>  	struct rtl_efuse *rtlefuse = rtl_efuse(rtl_priv(hw));
> -	u8 efuse_tbl[rtlpriv->cfg->maps[EFUSE_HWSET_MAX_SIZE]];
> +	u8 *efuse_tbl;
>  	u8 rtemp8[1];
>  	u16 efuse_addr = 0;
>  	u8 offset, wren;
> @@ -243,7 +243,7 @@ void read_efuse(struct ieee80211_hw *hw, u16 _offset, u16 _size_byte, u8 *pbuf)
>  		rtlpriv->cfg->maps[EFUSE_MAX_SECTION_MAP];
>  	const u32 efuse_real_content_len =
>  		rtlpriv->cfg->maps[EFUSE_REAL_CONTENT_SIZE];
> -	u16 efuse_word[efuse_max_section][EFUSE_MAX_WORD_UNIT];
> +	u16 **efuse_word;
>  	u16 efuse_utilized = 0;
>  	u8 efuse_usage;
>  
> @@ -254,9 +254,26 @@ void read_efuse(struct ieee80211_hw *hw, u16 _offset, u16 _size_byte, u8 *pbuf)
>  		return;
>  	}
>  
> +	efuse_tbl = kmalloc(rtlpriv->cfg->maps[EFUSE_HWSET_MAX_SIZE] *
> +			sizeof(*efuse_tbl), GFP_ATOMIC);

sizeof(*efuse_tbl) is a complicated way to say 1.  Just say:

	efuse_tbl = kmalloc(rtlpriv->cfg->maps[EFUSE_HWSET_MAX_SIZE], GFP_ATOMIC);

Why is it GFP_ATOMIC btw?  That wasn't immediately clear to me and I
didn't spend a lot of time looking.

> +	if (efuse_tbl == NULL)
> +		return;
> +
> +	efuse_word = kcalloc(EFUSE_MAX_WORD_UNIT, sizeof(*efuse_word),
> +			GFP_ATOMIC);
> +	if (efuse_word == NULL)
> +		goto out;
> +
> +	for (i = 0; i < EFUSE_MAX_WORD_UNIT; i++) {
> +		efuse_word[i] = kmalloc(efuse_max_section *
> +				sizeof(**efuse_word), GFP_ATOMIC);
> +		if (efuse_word[i] == NULL)
> +			goto done;
> +	}


Why is this so complicated?  Why not just:

	efuse_word = kmalloc(sizeof(*efuse_word) * efuse_max_section *
			     EFUSE_MAX_WORD_UNIT, GFP_ATOMIC);


> +
>  	for (i = 0; i < efuse_max_section; i++)
>  		for (j = 0; j < EFUSE_MAX_WORD_UNIT; j++)
> -			efuse_word[i][j] = 0xFFFF;
> +			efuse_word[j][i] = 0xFFFF;

Why are you re-ordering things here?

regards,
dan carpenter

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