Re: [BUG] bus: mhi: possible deadlock in mhi_pm_disable_transition() and mhi_async_power_up()

[Manivannan Sadhasivam <mani@kernel.org>]

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.