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From:   Jia-Ju Bai <baijiaju1990@gmail.com>
Subject: [BUG] staging: wfx: possible deadlock in wfx_conf_tx() and
 wfx_add_interface()
To:     jerome.pouiller@silabs.com, Greg KH <gregkh@linuxfoundation.org>
Cc:     linux-staging@lists.linux.dev,
        linux-kernel <linux-kernel@vger.kernel.org>
Message-ID: <6f489bf2-bac0-8030-7ea5-6f5c12daa568@gmail.com>
Date:   Tue, 1 Feb 2022 15:09:34 +0800
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Hello,

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

wfx_conf_tx()
   mutex_lock(&wdev->conf_mutex); --> Line 225 (Lock A)
   wfx_update_pm()
     wait_for_completion_timeout(&wvif->set_pm_mode_complete, ...); --> 
Line 3019 (Wait X)

wfx_add_interface()
   mutex_lock(&wdev->conf_mutex); --> Line 737 (Lock A)
   complete(&wvif->set_pm_mode_complete); --> Line 758 (Wake X)

When wfx_conf_tx() is executed, "Wait X" is performed by holding "Lock 
A". If wfx_add_interface() is executed at this time, "Wake X" cannot be 
performed to wake up "Wait X" in wfx_conf_tx(), because "Lock A" has 
been already hold by wfx_conf_tx(), 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