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

[Jia-Ju Bai]

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