linux-kernel - Re: [PATCH] [v2] net: hns3: reduce stack usage in hclge_dbg_dump_tm

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Message-ID: <8f5f9a4b-f809-44cb-8f26-05e39b29dfb6@wanadoo.fr>
Date:   Mon, 4 Dec 2023 19:54:20 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Arnd Bergmann <arnd@...nel.org>,
        Yisen Zhuang <yisen.zhuang@...wei.com>,
        Salil Mehta <salil.mehta@...wei.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Jijie Shao <shaojijie@...wei.com>,
        Hao Chen <chenhao418@...wei.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [v2] net: hns3: reduce stack usage in
 hclge_dbg_dump_tm_pri()

Le 04/12/2023 à 09:57, Arnd Bergmann a écrit :
> From: Arnd Bergmann <arnd@...db.de>
> 
> This function exceeds the stack frame warning limit:
> 
> drivers/net/ethernet/hisilicon/hns3/hns3pf/hclge_debugfs.c: In function 'hclge_dbg_dump_tm_pri':
> drivers/net/ethernet/hisilicon/hns3/hns3pf/hclge_debugfs.c:1039:1: error: the frame size of 1408 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
> 
> Use dynamic allocation for the largest stack object instead. It
> would be nice to rewrite this file to completely avoid the extra
> buffer and just use the one that was already allocated by debugfs,
> but that is a much larger change.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> v2: fix error handling leak
> ---
>   .../hisilicon/hns3/hns3pf/hclge_debugfs.c     | 21 ++++++++++++-------
>   1 file changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/ethernet/hisilicon/hns3/hns3pf/hclge_debugfs.c b/drivers/net/ethernet/hisilicon/hns3/hns3pf/hclge_debugfs.c
> index ff3f8f424ad9..8f94e13c1edf 100644
> --- a/drivers/net/ethernet/hisilicon/hns3/hns3pf/hclge_debugfs.c
> +++ b/drivers/net/ethernet/hisilicon/hns3/hns3pf/hclge_debugfs.c
> @@ -981,7 +981,7 @@ static const struct hclge_dbg_item tm_pri_items[] = {
>   
>   static int hclge_dbg_dump_tm_pri(struct hclge_dev *hdev, char *buf, int len)
>   {
> -	char data_str[ARRAY_SIZE(tm_pri_items)][HCLGE_DBG_DATA_STR_LEN];
> +	char *data_str;
>   	struct hclge_tm_shaper_para c_shaper_para, p_shaper_para;
>   	char *result[ARRAY_SIZE(tm_pri_items)], *sch_mode_str;
>   	char content[HCLGE_DBG_TM_INFO_LEN];
> @@ -992,8 +992,13 @@ static int hclge_dbg_dump_tm_pri(struct hclge_dev *hdev, char *buf, int len)
>   	if (ret)
>   		return ret;
>   
> +	data_str = kcalloc(ARRAY_SIZE(tm_pri_items), HCLGE_DBG_DATA_STR_LEN,
> +			   GFP_KERNEL);
> +	if (!data_str)
> +		return -ENOMEM;
> +
>   	for (i = 0; i < ARRAY_SIZE(tm_pri_items); i++)
> -		result[i] = &data_str[i][0];
> +		result[i] = &data_str[i * HCLGE_DBG_DATA_STR_LEN];
>   
>   	hclge_dbg_fill_content(content, sizeof(content), tm_pri_items,
>   			       NULL, ARRAY_SIZE(tm_pri_items));
> @@ -1002,23 +1007,23 @@ static int hclge_dbg_dump_tm_pri(struct hclge_dev *hdev, char *buf, int len)
>   	for (i = 0; i < pri_num; i++) {
>   		ret = hclge_tm_get_pri_sch_mode(hdev, i, &sch_mode);
>   		if (ret)
> -			return ret;
> +			goto out;
>   
>   		ret = hclge_tm_get_pri_weight(hdev, i, &weight);
>   		if (ret)
> -			return ret;
> +			goto out;
>   
>   		ret = hclge_tm_get_pri_shaper(hdev, i,
>   					      HCLGE_OPC_TM_PRI_C_SHAPPING,
>   					      &c_shaper_para);
>   		if (ret)
> -			return ret;
> +			goto out;
>   
>   		ret = hclge_tm_get_pri_shaper(hdev, i,
>   					      HCLGE_OPC_TM_PRI_P_SHAPPING,
>   					      &p_shaper_para);
>   		if (ret)
> -			return ret;
> +			goto out;
>   
>   		sch_mode_str = sch_mode & HCLGE_TM_TX_SCHD_DWRR_MSK ? "dwrr" :
>   			       "sp";
> @@ -1035,7 +1040,9 @@ static int hclge_dbg_dump_tm_pri(struct hclge_dev *hdev, char *buf, int len)
>   		pos += scnprintf(buf + pos, len - pos, "%s", content);
>   	}
>   
> -	return 0;
> +out:
> +	kfree(data_str);
> +	return ret;
>   }
>   
>   static const struct hclge_dbg_item tm_qset_items[] = {

Hi,
could :
    pos += scnprintf(buf + pos, len - pos, "%s", <something>);
be more widely used to avoid the alloc()/free() + copy of strings?

CJ