fix deadlock in audioflinger::createEffect()

commit 5baf2af5 introduced a regression by calling
getOutputForEffect() with AudioFLinger main mutex locked.
The locking order must always be AudioPolicyService mutex then
AudioFlinger then ThreadBase mutex.

Bug: 10916796.
Change-Id: Ide34a2d84dbb06dbb35abd0640d91b01b0ac4d40

1 files changed, 4 insertions, 0 deletions

diff --git a/services/audioflinger/Effects.h b/services/audioflinger/Effects.h
index c35cff0..b717857 100644
--- a/services/audioflinger/Effects.h
+++ b/services/audioflinger/Effects.h
@@ -25,6 +25,10 @@
 // state changes or resource modifications. Always respect the following order
 // if multiple mutexes must be acquired to avoid cross deadlock:
 // AudioFlinger -> ThreadBase -> EffectChain -> EffectModule
+// In addition, methods that lock the AudioPolicyService mutex (getOutputForEffect(),
+// startOutput()...) should never be called with AudioFlinger or Threadbase mutex locked
+// to avoid cross deadlock with other clients calling AudioPolicyService methods that in turn
+// call AudioFlinger thus locking the same mutexes in the reverse order.
 
 // The EffectModule class is a wrapper object controlling the effect engine implementation
 // in the effect library. It prevents concurrent calls to process() and command() functions