Re: [PATCH] wifi: ath11k: fix ath11k_mac_op_remain_on_channel() stack usage

[Jeff Johnson <quic_jjohnson@xxxxxxxxxxx>]

On 9/25/2023 5:46 AM, Dmitry Antipov wrote:
> When compiling with clang 16.0.6, I've noticed the following:
>
> drivers/net/wireless/ath/ath11k/mac.c:8903:12: warning: stack frame
> size (1032) exceeds limit (1024) in 'ath11k_mac_op_remain_on_channel'
> [-Wframe-larger-than]
> static int ath11k_mac_op_remain_on_channel(struct ieee80211_hw *hw,
>             ^
> 68/1032 (6.59%) spills, 964/1032 (93.41%) variables
>
> So switch to kzalloc()'ed instance of 'struct scan_req_params' like
> it's done in 'ath11k_mac_op_hw_scan()'. Compile tested only.
>
> Signed-off-by: Dmitry Antipov <dmantipov@xxxxxxxxx>
> ---
>   drivers/net/wireless/ath/ath11k/mac.c | 43 +++++++++++++++------------
>   1 file changed, 24 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/net/wireless/ath/ath11k/mac.c b/drivers/net/wireless/ath/ath11k/mac.c
> index 6ed036b51dba..c7d51f6aeede 100644
> --- a/drivers/net/wireless/ath/ath11k/mac.c
> +++ b/drivers/net/wireless/ath/ath11k/mac.c
> @@ -8908,7 +8908,7 @@ static int ath11k_mac_op_remain_on_channel(struct ieee80211_hw *hw,
>   {
>   	struct ath11k *ar = hw->priv;
>   	struct ath11k_vif *arvif = ath11k_vif_to_arvif(vif);
> -	struct scan_req_params arg;
> +	struct scan_req_params *arg = NULL;
>   	int ret;
>   	u32 scan_time_msec;
>   
> @@ -8940,27 +8940,31 @@ static int ath11k_mac_op_remain_on_channel(struct ieee80211_hw *hw,
>   
>   	scan_time_msec = ar->hw->wiphy->max_remain_on_channel_duration * 2;
>   
> -	memset(&arg, 0, sizeof(arg));
> -	ath11k_wmi_start_scan_init(ar, &arg);
> -	arg.num_chan = 1;
> -	arg.chan_list = kcalloc(arg.num_chan, sizeof(*arg.chan_list),
> -				GFP_KERNEL);
> -	if (!arg.chan_list) {
> +	arg = kzalloc(sizeof(*arg), GFP_KERNEL);
> +	if (!arg) {
> +		ret = -ENOMEM;
> +		goto exit;
> +	}
> +	ath11k_wmi_start_scan_init(ar, arg);
> +	arg->num_chan = 1;
> +	arg->chan_list = kcalloc(arg->num_chan, sizeof(*arg->chan_list),
> +				 GFP_KERNEL);
> +	if (!arg->chan_list) {
>   		ret = -ENOMEM;
>   		goto exit;
>   	}
>   
> -	arg.vdev_id = arvif->vdev_id;
> -	arg.scan_id = ATH11K_SCAN_ID;
> -	arg.chan_list[0] = chan->center_freq;
> -	arg.dwell_time_active = scan_time_msec;
> -	arg.dwell_time_passive = scan_time_msec;
> -	arg.max_scan_time = scan_time_msec;
> -	arg.scan_flags |= WMI_SCAN_FLAG_PASSIVE;
> -	arg.scan_flags |= WMI_SCAN_FILTER_PROBE_REQ;
> -	arg.burst_duration = duration;
> -
> -	ret = ath11k_start_scan(ar, &arg);
> +	arg->vdev_id = arvif->vdev_id;
> +	arg->scan_id = ATH11K_SCAN_ID;
> +	arg->chan_list[0] = chan->center_freq;
> +	arg->dwell_time_active = scan_time_msec;
> +	arg->dwell_time_passive = scan_time_msec;
> +	arg->max_scan_time = scan_time_msec;
> +	arg->scan_flags |= WMI_SCAN_FLAG_PASSIVE;
> +	arg->scan_flags |= WMI_SCAN_FILTER_PROBE_REQ;
> +	arg->burst_duration = duration;
> +
> +	ret = ath11k_start_scan(ar, arg);
>   	if (ret) {
>   		ath11k_warn(ar->ab, "failed to start roc scan: %d\n", ret);
>   
> @@ -8986,8 +8990,9 @@ static int ath11k_mac_op_remain_on_channel(struct ieee80211_hw *hw,
>   	ret = 0;
>   
>   free_chan_list:
> -	kfree(arg.chan_list);
> +	kfree(arg->chan_list);
>   exit:
> +	kfree(arg);

consider adding a free_arg: label which you'd goto if the chan_list 
allocation fails. exit: would continue to just have the mutex_unlock()

with that change you no longer need the arg = NULL initializer

>   	mutex_unlock(&ar->conf_mutex);
>   	return ret;
>   }