Hi, Thanks for the report! 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. > As per the MHI design, we can be sure that mhi_pm_disable_transition() won't be called until wait_event_timeout() completes in mhi_async_power_up(). So this deadlock is not possible in practical. Thanks, Mani > 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 > > >
