[BUG] net: netronome: nfp: possible deadlock in nfp_cpp_area_acquire() and nfp_cpp_area_release()

Hello,

My static analysis tool reports a possible deadlock in the nfp driver in 
Linux 5.16:

nfp_cpp_area_acquire()
   mutex_lock(&area->mutex); --> Line 455 (Lock A)
   __nfp_cpp_area_acquire()
     wait_event_interruptible(area->cpp->waitq, ...) --> Line 427 (Wait X)

nfp_cpp_area_release()
   mutex_lock(&area->mutex); --> Line 502 (Lock A)
   wake_up_interruptible_all(&area->cpp->waitq); --> Line 508 (Wake X)

When nfp_cpp_area_acquire() is executed, "Wait X" is performed by 
holding "Lock A". If nfp_cpp_area_release() is executed at this time, 
"Wake X" cannot be performed to wake up "Wait X" in 
nfp_cpp_area_acquire(), because "Lock A" has been already hold by 
nfp_cpp_area_acquire(), causing a possible deadlock.

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

On Wed, 9 Feb 2022 10:50:44 +0800 Jia-Ju Bai wrote:

Hello,

My static analysis tool reports a possible deadlock in the nfp driver in 
Linux 5.16:

nfp_cpp_area_acquire()
   mutex_lock(&area->mutex); --> Line 455 (Lock A)
   __nfp_cpp_area_acquire()
     wait_event_interruptible(area->cpp->waitq, ...) --> Line 427 (Wait X)

nfp_cpp_area_release()
   mutex_lock(&area->mutex); --> Line 502 (Lock A)
   wake_up_interruptible_all(&area->cpp->waitq); --> Line 508 (Wake X)

When nfp_cpp_area_acquire() is executed, "Wait X" is performed by 
holding "Lock A". If nfp_cpp_area_release() is executed at this time, 
"Wake X" cannot be performed to wake up "Wait X" in 
nfp_cpp_area_acquire(), because "Lock A" has been already hold by 
nfp_cpp_area_acquire(), causing a possible deadlock.

I am not quite sure whether this possible problem is real and how to fix 
it if it is real.

It's not.

Any feedback would be appreciated, thanks :)


Best wishes,
Jia-Ju Bai