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From: Pkshih <pkshih@realtek.com>
To: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: "linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>,
	"tony0620emma@gmail.com" <tony0620emma@gmail.com>,
	"kvalo@codeaurora.org" <kvalo@codeaurora.org>,
	"johannes@sipsolutions.net" <johannes@sipsolutions.net>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Neo Jou <neojou@gmail.com>,
	Jernej Skrabec <jernej.skrabec@gmail.com>
Subject: RE: [PATCH RFC v1 5/7] rtw88: Configure the registers from rtw_bf_assoc() outside the RCU lock
Date: Mon, 26 Jul 2021 07:22:30 +0000	[thread overview]
Message-ID: <c60c9877f491411c915c64d1fc7a797a@realtek.com> (raw)
In-Reply-To: <CAFBinCAJNqbpoqSSFYYBJg818KHCKx5nFzsKZdR=D+sTXQj6dg@mail.gmail.com>


> -----Original Message-----
> From: Martin Blumenstingl [mailto:martin.blumenstingl@googlemail.com]
> Sent: Monday, July 26, 2021 5:36 AM
> To: Pkshih
> Cc: linux-wireless@vger.kernel.org; tony0620emma@gmail.com; kvalo@codeaurora.org;
> johannes@sipsolutions.net; netdev@vger.kernel.org; linux-kernel@vger.kernel.org; Neo Jou; Jernej
> Skrabec
> Subject: Re: [PATCH RFC v1 5/7] rtw88: Configure the registers from rtw_bf_assoc() outside the RCU lock
> 
> Hi Ping-Ke,
> 
> On Mon, Jul 19, 2021 at 7:47 AM Pkshih <pkshih@realtek.com> wrote:
> [...]
> > 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();
> I agree that reducing the amount of code under the lock will help my
> use-case as well
> in your code-example I am wondering if we should change
>   struct ieee80211_sta_vht_cap *vht_cap;
>   vht_cap = &sta->vht_cap;
> to
>   struct ieee80211_sta_vht_cap vht_cap;
>   vht_cap = sta->vht_cap;
> 
> My thinking is that ieee80211_sta may be freed in parallel to this code running.
> If that cannot happen then your code will be fine.
> 
> So I am hoping that you can also share your thoughts on this one.
> 

When we enter rtw_bf_assoc(), the mutex rtwdev->mutex is held; as well as
rtw_sta_add()/rtw_sta_remove(). So, I think it cannot happen that ieee80211_sta
was freed in parallel.

--
Ping-Ke


  reply	other threads:[~2021-07-26  7:22 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-17 20:40 [PATCH RFC v1 0/7] rtw88: prepare locking for SDIO support Martin Blumenstingl
2021-07-17 20:40 ` [PATCH RFC v1 1/7] mac80211: Add stations iterator where the iterator function may sleep Martin Blumenstingl
2021-07-19  5:46   ` Pkshih
2021-07-19  6:30   ` Johannes Berg
2021-07-17 20:40 ` [PATCH RFC v1 2/7] rtw88: Use rtw_iterate_vifs where the iterator reads or writes registers Martin Blumenstingl
2021-07-19  5:47   ` Pkshih
2021-07-25 21:31     ` Martin Blumenstingl
2021-07-26  7:22       ` Pkshih
2021-07-17 20:40 ` [PATCH RFC v1 3/7] rtw88: Use rtw_iterate_stas " Martin Blumenstingl
2021-07-19  6:36   ` Johannes Berg
2021-07-25 21:51     ` Martin Blumenstingl
2021-07-26  7:22       ` Pkshih
2021-08-09 20:00         ` Johannes Berg
2021-07-17 20:40 ` [PATCH RFC v1 4/7] rtw88: Replace usage of rtw_iterate_keys_rcu() with rtw_iterate_keys() Martin Blumenstingl
2021-07-17 20:40 ` [PATCH RFC v1 5/7] rtw88: Configure the registers from rtw_bf_assoc() outside the RCU lock Martin Blumenstingl
2021-07-19  5:47   ` Pkshih
2021-07-25 21:36     ` Martin Blumenstingl
2021-07-26  7:22       ` Pkshih [this message]
2021-07-17 20:40 ` [PATCH RFC v1 6/7] rtw88: hci: Convert rf_lock from a spinlock to a mutex Martin Blumenstingl
2021-07-17 20:40 ` [PATCH RFC v1 7/7] rtw88: fw: Convert h2c.lock " Martin Blumenstingl
2021-07-19  5:52 ` [PATCH RFC v1 0/7] rtw88: prepare locking for SDIO support Pkshih

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