audio policy: fix preemtible capture race

Because a preemtible capture session can preempt another one,
we end up in an endless loop situation were each session is allowed to restart
after being preempted, thus preempting the other one which restarts and so on.

To avoid this situation, we store which audio session was preempted when
a particular input started and prevent preemption of this active input by this session.
We also inherit sessions from the preempted input to avoid a 3 way preemption loop etc...

Bug: 24007220.
Change-Id: I0eab5299440ef3ab9e987635dc9a300cf42f2c79

3 files changed, 41 insertions, 3 deletions

diff --git a/services/audiopolicy/common/managerdefinitions/include/AudioInputDescriptor.h b/services/audiopolicy/common/managerdefinitions/include/AudioInputDescriptor.h
index 18bcfdb..48d09ed 100644
--- a/services/audiopolicy/common/managerdefinitions/include/AudioInputDescriptor.h
+++ b/services/audiopolicy/common/managerdefinitions/include/AudioInputDescriptor.h
@@ -56,9 +56,21 @@ public:
             const struct audio_port_config *srcConfig = NULL) const;
     virtual sp<AudioPort> getAudioPort() const { return mProfile; }
     void toAudioPort(struct audio_port *port) const;
+    void setPreemptedSessions(const SortedVector<audio_session_t>& sessions);
+    SortedVector<audio_session_t> getPreemptedSessions() const;
+    bool hasPreemptedSession(audio_session_t session) const;
+    void clearPreemptedSessions();
 
 private:
     audio_port_handle_t           mId;
+    // Because a preemtible capture session can preempt another one, we end up in an endless loop
+    // situation were each session is allowed to restart after being preempted,
+    // thus preempting the other one which restarts and so on.
+    // To avoid this situation, we store which audio session was preempted when
+    // a particular input started and prevent preemption of this active input by this session.
+    // We also inherit sessions from the preempted input to avoid a 3 way preemption loop etc...
+    SortedVector<audio_session_t> mPreemptedSessions;
+
 };
 
 class AudioInputCollection :
diff --git a/services/audiopolicy/common/managerdefinitions/src/AudioInputDescriptor.cpp b/services/audiopolicy/common/managerdefinitions/src/AudioInputDescriptor.cpp
index 937160b..626fdae 100644
--- a/services/audiopolicy/common/managerdefinitions/src/AudioInputDescriptor.cpp
+++ b/services/audiopolicy/common/managerdefinitions/src/AudioInputDescriptor.cpp
@@ -93,6 +93,26 @@ void AudioInputDescriptor::toAudioPort(struct audio_port *port) const
     port->ext.mix.latency_class = AUDIO_LATENCY_NORMAL;
 }
 
+void AudioInputDescriptor::setPreemptedSessions(const SortedVector<audio_session_t>& sessions)
+{
+    mPreemptedSessions = sessions;
+}
+
+SortedVector<audio_session_t> AudioInputDescriptor::getPreemptedSessions() const
+{
+    return mPreemptedSessions;
+}
+
+bool AudioInputDescriptor::hasPreemptedSession(audio_session_t session) const
+{
+    return (mPreemptedSessions.indexOf(session) >= 0);
+}
+
+void AudioInputDescriptor::clearPreemptedSessions()
+{
+    mPreemptedSessions.clear();
+}
+
 status_t AudioInputDescriptor::dump(int fd)
 {
     const size_t SIZE = 256;
diff --git a/services/audiopolicy/managerdefault/AudioPolicyManager.cpp b/services/audiopolicy/managerdefault/AudioPolicyManager.cpp
index dfb477d..8419ed5 100644
--- a/services/audiopolicy/managerdefault/AudioPolicyManager.cpp
+++ b/services/audiopolicy/managerdefault/AudioPolicyManager.cpp
@@ -1485,10 +1485,15 @@ status_t AudioPolicyManager::startInput(audio_io_handle_t input,
             // If the already active input uses AUDIO_SOURCE_HOTWORD then it is closed,
             // otherwise the active input continues and the new input cannot be started.
             sp<AudioInputDescriptor> activeDesc = mInputs.valueFor(activeInput);
-            if (activeDesc->mInputSource == AUDIO_SOURCE_HOTWORD) {
+            if ((activeDesc->mInputSource == AUDIO_SOURCE_HOTWORD) &&
+                    !activeDesc->hasPreemptedSession(session)) {
                 ALOGW("startInput(%d) preempting low-priority input %d", input, activeInput);
-                stopInput(activeInput, activeDesc->mSessions.itemAt(0));
-                releaseInput(activeInput, activeDesc->mSessions.itemAt(0));
+                audio_session_t activeSession = activeDesc->mSessions.itemAt(0);
+                SortedVector<audio_session_t> sessions = activeDesc->getPreemptedSessions();
+                sessions.add(activeSession);
+                inputDesc->setPreemptedSessions(sessions);
+                stopInput(activeInput, activeSession);
+                releaseInput(activeInput, activeSession);
             } else {
                 ALOGE("startInput(%d) failed: other input %d already started", input, activeInput);
                 return INVALID_OPERATION;
@@ -1592,6 +1597,7 @@ status_t AudioPolicyManager::stopInput(audio_io_handle_t input,
         if (mInputs.activeInputsCount() == 0) {
             SoundTrigger::setCaptureState(false);
         }
+        inputDesc->clearPreemptedSessions();
     }
     return NO_ERROR;
 }