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From:   Jia-Ju Bai <baijiaju1990@gmail.com>
Subject: [BUG] bus: mhi: possible deadlock in mhi_pm_disable_transition() and
 mhi_async_power_up()
To:     mani@kernel.org, hemantk@codeaurora.org, bbhatt@codeaurora.org,
        loic.poulain@linaro.org, jhugo@codeaurora.org
Cc:     linux-arm-msm@vger.kernel.org,
        linux-kernel <linux-kernel@vger.kernel.org>
Message-ID: <d3a94b53-0d77-dafe-ce45-f9ab23278616@gmail.com>
Date:   Sat, 29 Jan 2022 10:56:30 +0800
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Hello,

My static analysis tool reports a possible deadlock in the mhi driver in 
Linux 5.10:

mhi_async_power_up()
   mutex_lock(&mhi_cntrl->pm_mutex); --> Line 933 (Lock A)
   wait_event_timeout(mhi_cntrl->state_event, ...) --> Line 985 (Wait X)
   mutex_unlock(&mhi_cntrl->pm_mutex); --> Line 1040 (Unlock A)

mhi_pm_disable_transition()
   mutex_lock(&mhi_cntrl->pm_mutex); --> Line 463 (Lock A)
   wake_up_all(&mhi_cntrl->state_event); --> Line 474 (Wake X)
   mutex_unlock(&mhi_cntrl->pm_mutex); --> Line 524 (Unlock A)
   wake_up_all(&mhi_cntrl->state_event); --> Line 526 (Wake X)

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