Hello,
My static analysis tool reports a possible deadlock in the radeon driver
in Linux 5.16:
#BUG 1
radeon_dpm_change_power_state_locked()
mutex_lock(&rdev->ring_lock); --> Line 1133 (Lock A)
radeon_fence_wait_empty()
radeon_fence_wait_seq_timeout()
wait_event_timeout(rdev->fence_queue, ...) --> Line 504 (Wait X)
radeon_ring_backup()
mutex_lock(&rdev->ring_lock); --> Line 289(Lock A)
radeon_fence_count_emitted()
radeon_fence_process()
wake_up_all(&rdev->fence_queue); --> Line 323 (Wake X)
When radeon_dpm_change_power_state_locked() is executed, "Wait X" is
performed by holding "Lock A". If radeon_ring_backup() is executed at
this time, "Wake X" cannot be performed to wake up "Wait X" in
radeon_dpm_change_power_state_locked(), because "Lock A" has been
already hold by radeon_dpm_change_power_state_locked(), causing a
possible deadlock.
I find that "Wait X" is performed with a timeout MAX_SCHEDULE_TIMEOUT,
to relieve the possible deadlock; but I think this timeout can cause
inefficient execution.
#BUG 2
radeon_ring_lock()
mutex_lock(&rdev->ring_lock); --> Line 147 (Lock A)
radeon_ring_alloc()
radeon_fence_wait_next()
radeon_fence_wait_seq_timeout()
wait_event_timeout(rdev->fence_queue, ...) --> Line 504 (Wait X)
radeon_ring_backup()
mutex_lock(&rdev->ring_lock); --> Line 289(Lock A)
radeon_fence_count_emitted()
radeon_fence_process()
wake_up_all(&rdev->fence_queue); --> Line 323 (Wake X)
When radeon_ring_lock() is executed, "Wait X" is performed by holding
"Lock A". If radeon_ring_backup() is executed at this time, "Wake X"
cannot be performed to wake up "Wait X" in radeon_ring_lock(), because
"Lock A" has been already hold by radeon_ring_lock(), causing a possible
deadlock.
I find that "Wait X" is performed with a timeout MAX_SCHEDULE_TIMEOUT,
to relieve the possible deadlock; but I think this timeout can cause
inefficient execution.
I am not quite sure whether these possible problems are real and how to
fix them if they are real.
Any feedback would be appreciated, thanks :)
Best wishes,
Jia-Ju Bai
