netdev - [BUG] intersil: p54: possible deadlock in p54_remove_interface() and p54

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Date:   Mon, 7 Feb 2022 23:31:26 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     chunkeey@...glemail.com, kvalo@...nel.org, davem@...emloft.net,
        kuba@...nel.org
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [BUG] intersil: p54: possible deadlock in p54_remove_interface() and
 p54_stop()

Hello,

My static analysis tool reports a possible deadlock in the p54 driver in 
Linux 5.16:

p54_remove_interface()
   mutex_lock(&priv->conf_mutex); --> Line 262 (Lock A)
wait_for_completion_interruptible_timeout(&priv->beacon_comp, HZ); --> 
Line 271 (Wait X)

p54_stop()
   mutex_lock(&priv->conf_mutex); --> Line 208 (Lock A)
   p54p_stop() (call via priv->stop)
     p54_free_skb()
       p54_tx_qos_accounting_free()
         complete(&priv->beacon_comp); --> Line 230 (Wake X)

When p54_remove_interface() is executed, "Wait X" is performed by 
holding "Lock A". If p54_stop() is executed at this time, "Wake X" 
cannot be performed to wake up "Wait X" in p54_remove_interface(), 
because "Lock A" has been already hold by p54_remove_interface(), 
causing a possible deadlock.
I find that "Wait X" is performed with a timeout, to relieve the 
possible deadlock; but I think this timeout can cause inefficient execution.

I am not quite sure whether this possible problem is real and how to fix 
it if it is real.
Any feedback would be appreciated, thanks :)

Best wishes,
Jia-Ju Bai