Received-SPF: pass (google.com: domain of linux-wireless-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Jia-Ju Bai <baijiaju1990@gmail.com>
To:     pontus.fuchs@gmail.com, Kalle Valo <kvalo@codeaurora.org>
Cc:     linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: [BUG] ar5523: possible deadlocks involving locking and waiting
 operations
Message-ID: <7c9bb278-5042-3bdc-9598-95a10e42f78d@gmail.com>
Date:   Tue, 8 Feb 2022 19:13:15 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101
 Thunderbird/68.4.1
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Content-Language: en-US
Precedence: bulk

Hello,

My static analysis tool reports two possible deadlocks in the ar5523 
driver in Linux 5.16:

#BUG 1
ar5523_hwconfig()
   mutex_lock(&ar->mutex); --> Line 1135 (Lock A)
   ar5523_flush_tx()
     wait_event_timeout(ar->tx_flush_waitq, ...) --> Line 926 (Wait X)

ar5523_tx_work()
   mutex_lock(&ar->mutex); --> Line 888 (Lock A)
   ar5523_tx_work_locked()
     ar5523_data_tx_pkt_put()
       wake_up(&ar->tx_flush_waitq); --> Line 727 (Wake X)

#BUG 2
ar5523_configure_filter()
   mutex_lock(&ar->mutex); --> Line 1331 (Lock A)
   ar5523_flush_tx()
     wait_event_timeout(ar->tx_flush_waitq, ...) --> Line 926 (Wait X)

ar5523_tx_work()
   mutex_lock(&ar->mutex); --> Line 888 (Lock A)
   ar5523_tx_work_locked()
     ar5523_data_tx_pkt_put()
       wake_up(&ar->tx_flush_waitq); --> Line 727 (Wake X)

When ar5523_hwconfig()/ar5523_configure_filter() is executed, "Wait X" 
is performed by holding "Lock A". If ar5523_tx_work() is executed at 
this time, "Wake X" cannot be performed to wake up "Wait X", because 
"Lock A" has been already held, causing possible deadlock.
I find that "Wait X" is performed with a timeout, to relieve the 
possible deadlocks; but I think this timeout can cause inefficient 
execution.

I am not quite sure whether these possible problems are real.
Any feedback would be appreciated, thanks :)


Best wishes,
Jia-Ju Bai