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Date:   Mon, 7 Feb 2022 12:15:04 +0530
From:   Manivannan Sadhasivam <mani@kernel.org>
To:     Daniel Thompson <daniel.thompson@linaro.org>
Cc:     Jia-Ju Bai <baijiaju1990@gmail.com>, hemantk@codeaurora.org,
        bbhatt@codeaurora.org, loic.poulain@linaro.org,
        jhugo@codeaurora.org, linux-arm-msm@vger.kernel.org,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [BUG] bus: mhi: possible deadlock in mhi_pm_disable_transition()
 and mhi_async_power_up()
Message-ID: <20220207064504.GC1905@thinkpad>
References: <d3a94b53-0d77-dafe-ce45-f9ab23278616@gmail.com>
 <20220201171540.2udq3x6r2swctzau@maple.lan>
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On Tue, Feb 01, 2022 at 05:15:40PM +0000, Daniel Thompson wrote:
> On Sat, Jan 29, 2022 at 10:56:30AM +0800, Jia-Ju Bai wrote:
> > 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 :)
> 
> Interesting find but I think it would be better to run your tool
> against more recent kernels to confirm any problem reports. In this
> case the code you mention looks like it was removed in v5.17-rc1
> (and should eventually make its way to the stable kernels too).
> 

Hmm, looks like the commit didn't apply cleanly to 5.10:
https://www.spinics.net/lists/stable/msg526754.html

Let send the fix up version.

Thanks,
Mani

> 
> Daniel.