Fix potential freezer thrashing

Currently a pending DO_FREEZE message stays in the message queue until
AMS tries to actually freeze it. If the OOM_ADJ happens to swing back
and forth, the app might be frozen and then unfrozen quickly. Fix the
issue by removing the pending DO_FREEZE message ASAP.

Bug: 188739027
Test: Move an app to foreground, its pending freeze status is cleared.
Change-Id: I369710d408e1d81bc169a620543909cb4ae6edf7

services/core/java/com/android/server/am/CachedAppOptimizer.java

@@ -881,7 +881,8 @@ public final class CachedAppOptimizer {
 
     @GuardedBy({"mAm", "mProcLock"})
     void freezeAppAsyncLSP(ProcessRecord app) {
-        if (mFreezeHandler.hasMessages(SET_FROZEN_PROCESS_MSG, app)) {
+        final ProcessCachedOptimizerRecord opt = app.mOptRecord;
+        if (opt.isPendingFreeze()) {
             // Skip redundant DO_FREEZE message
             return;
         }
@@ -890,21 +891,27 @@ public final class CachedAppOptimizer {
                 mFreezeHandler.obtainMessage(
                     SET_FROZEN_PROCESS_MSG, DO_FREEZE, 0, app),
                 mFreezerDebounceTimeout);
+        opt.setPendingFreeze(true);
+        if (DEBUG_FREEZER) {
+            Slog.d(TAG_AM, "Async freezing " + app.getPid() + " " + app.processName);
+        }
     }
 
     @GuardedBy({"mAm", "mProcLock"})
     void unfreezeAppLSP(ProcessRecord app) {
-        mFreezeHandler.removeMessages(SET_FROZEN_PROCESS_MSG, app);
-
         final int pid = app.getPid();
         final ProcessCachedOptimizerRecord opt = app.mOptRecord;
+        if (opt.isPendingFreeze()) {
+            // Remove pending DO_FREEZE message
+            mFreezeHandler.removeMessages(SET_FROZEN_PROCESS_MSG, app);
+            opt.setPendingFreeze(false);
+            if (DEBUG_FREEZER) {
+                Slog.d(TAG_AM, "Cancel freezing " + pid + " " + app.processName);
+            }
+        }
+
         opt.setFreezerOverride(false);
         if (!opt.isFrozen()) {
-            if (DEBUG_FREEZER) {
-                Slog.d(TAG_AM,
-                        "Skipping unfreeze for process " + pid + " "
-                        + app.processName + " (not frozen)");
-            }
             return;
         }
 
@@ -983,7 +990,12 @@ public final class CachedAppOptimizer {
     @GuardedBy({"mAm", "mProcLock"})
     void unscheduleFreezeAppLSP(ProcessRecord app) {
         if (mUseFreezer) {
-            mFreezeHandler.removeMessages(SET_FROZEN_PROCESS_MSG, app);
+            final ProcessCachedOptimizerRecord opt = app.mOptRecord;
+            if (opt.isPendingFreeze()) {
+                // Remove pending DO_FREEZE message
+                mFreezeHandler.removeMessages(SET_FROZEN_PROCESS_MSG, app);
+                opt.setPendingFreeze(false);
+            }
         }
     }
 
@@ -1278,6 +1290,8 @@ public final class CachedAppOptimizer {
             final boolean frozen;
             final ProcessCachedOptimizerRecord opt = proc.mOptRecord;
 
+            opt.setPendingFreeze(false);
+
             try {
                 // pre-check for locks to avoid unnecessary freeze/unfreeze operations
                 if (Process.hasFileLocks(pid)) {
@@ -1352,7 +1366,6 @@ public final class CachedAppOptimizer {
                 return;
             }
 
-
             if (DEBUG_FREEZER) {
                 Slog.d(TAG_AM, "froze " + pid + " " + name);
             }

services/core/java/com/android/server/am/OomAdjuster.java

@@ -3112,6 +3112,7 @@ public class OomAdjuster {
         // if an app is already frozen and shouldNotFreeze becomes true, immediately unfreeze
         if (opt.isFrozen() && opt.shouldNotFreeze()) {
             mCachedAppOptimizer.unfreezeAppLSP(app);
+            return;
         }
 
         final ProcessStateRecord state = app.mState;
@@ -3119,7 +3120,7 @@ public class OomAdjuster {
         if (state.getCurAdj() >= ProcessList.CACHED_APP_MIN_ADJ && !opt.isFrozen()
                 && !opt.shouldNotFreeze()) {
             mCachedAppOptimizer.freezeAppAsyncLSP(app);
-        } else if (state.getSetAdj() < ProcessList.CACHED_APP_MIN_ADJ && opt.isFrozen()) {
+        } else if (state.getSetAdj() < ProcessList.CACHED_APP_MIN_ADJ) {
             mCachedAppOptimizer.unfreezeAppLSP(app);
         }
     }

services/core/java/com/android/server/am/ProcessCachedOptimizerRecord.java

@@ -86,6 +86,12 @@ final class ProcessCachedOptimizerRecord {
     @GuardedBy("mProcLock")
     private boolean mFreezeExempt;
 
+    /**
+     * This process has been scheduled for freezing
+     */
+    @GuardedBy("mProcLock")
+    private boolean mPendingFreeze;
+
     @GuardedBy("mProcLock")
     long getLastCompactTime() {
         return mLastCompactTime;
@@ -171,6 +177,16 @@ final class ProcessCachedOptimizerRecord {
         return mFreezeExempt;
     }
 
+    @GuardedBy("mProcLock")
+    void setPendingFreeze(boolean freeze) {
+        mPendingFreeze = freeze;
+    }
+
+    @GuardedBy("mProcLock")
+    boolean isPendingFreeze() {
+        return mPendingFreeze;
+    }
+
     @GuardedBy("mProcLock")
     void setFreezeExempt(boolean exempt) {
         mFreezeExempt = exempt;
@@ -190,6 +206,7 @@ final class ProcessCachedOptimizerRecord {
         pw.print(prefix); pw.print("lastCompactTime="); pw.print(mLastCompactTime);
         pw.print(" lastCompactAction="); pw.println(mLastCompactAction);
         pw.print(prefix); pw.print("isFreezeExempt="); pw.print(mFreezeExempt);
+        pw.print(" isPendingFreeze="); pw.print(mPendingFreeze);
         pw.print(" " + IS_FROZEN + "="); pw.println(mFrozen);
     }
 }