RE: [PATCH RFC v1 5/7] rtw88: Configure the registers from rtw_bf_assoc() outside the RCU lock

Pkshih
2021-07-19T05:47:29Z

> -----Original Message-----
> From: Martin Blumenstingl [mailto:martin.blumenstingl@googlemail.com]
> Sent: Sunday, July 18, 2021 4:41 AM
> To: linux-wireless@vger.kernel.org
> Cc: tony0620emma@gmail.com; kvalo@codeaurora.org; johannes@sipsolutions.net; netdev@vger.kernel.org;
> linux-kernel@vger.kernel.org; Neo Jou; Jernej Skrabec; Martin Blumenstingl
> Subject: [PATCH RFC v1 5/7] rtw88: Configure the registers from rtw_bf_assoc() outside the RCU lock
>
> Upcoming SDIO support may sleep in the read/write handlers. Configure
> the chip's BFEE configuration set from rtw_bf_assoc() outside the
> rcu_read_lock section to prevent a "scheduling while atomic" issue.
>
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
> ---
> drivers/net/wireless/realtek/rtw88/bf.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/wireless/realtek/rtw88/bf.c b/drivers/net/wireless/realtek/rtw88/bf.c
> index aff70e4ae028..06034d5d6f6c 100644
> --- a/drivers/net/wireless/realtek/rtw88/bf.c
> +++ b/drivers/net/wireless/realtek/rtw88/bf.c
> @@ -39,6 +39,7 @@ void rtw_bf_assoc(struct rtw_dev *rtwdev, struct ieee80211_vif *vif,
> struct ieee80211_sta_vht_cap *vht_cap;
> struct ieee80211_sta_vht_cap *ic_vht_cap;
> const u8 *bssid = bss_conf->bssid;
> + bool config_bfee = false;
> u32 sound_dim;
> u8 i;
>

The rcu_read_lock() in this function is used to access ieee80211_find_sta() and protect 'sta'.
A simple way is to shrink the critical section, like:

rcu_read_lock();

sta = ieee80211_find_sta(vif, bssid);
if (!sta) {
rtw_warn(rtwdev, "failed to find station entry for bss %pM\n",
bssid);
rcu_read_unlock();
}

vht_cap = &sta->vht_cap;

rcu_read_unlock();

--
Ping-Ke