Do not freeze system_server

In early testing, freezing the current process generated an error but
did no harm.  Now it does harm.  This CL disables freezing because of
an ANR timeout if the target pid is 0 (often passed in to signify
"self") or the pid of system_server.

Flag: com.android.server.utils.anr_timer_freezer
Bug: 391491604
Test: atest
 * FrameworksServicesTests:AnrTimerTest
 * FrameworksServicesTests:com.android.server.am
 * FrameworksMockingServicesTests:com.android.server.am
Change-Id: I78189987f4dee398a02f6ca50df9d4e1a83b5419

1 files changed, 8 insertions, 2 deletions

diff --git a/services/core/jni/com_android_server_utils_AnrTimer.cpp b/services/core/jni/com_android_server_utils_AnrTimer.cpp
index 2add5b09f15b..24909ac6150b 100644
--- a/services/core/jni/com_android_server_utils_AnrTimer.cpp
+++ b/services/core/jni/com_android_server_utils_AnrTimer.cpp
@@ -101,6 +101,9 @@ nsecs_t now() {
     return systemTime(SYSTEM_TIME_MONOTONIC);
 }
 
+// The current process.  This is cached here on startup.
+const pid_t sThisProcess = getpid();
+
 // Return true if the process exists and false if we cannot know.
 bool processExists(pid_t pid) {
     char path[PATH_MAX];
@@ -726,7 +729,7 @@ class AnrTimerService::Timer {
             uid(uid),
             timeout(timeout),
             extend(extend),
-            freeze(pid != 0 && freeze),
+            freeze(freeze),
             split(trace.earlyTimeout),
             action(trace.action),
             status(Running),
@@ -1188,8 +1191,11 @@ const char* AnrTimerService::statusString(Status s) {
 }
 
 AnrTimerService::timer_id_t AnrTimerService::start(int pid, int uid, nsecs_t timeout) {
+    // Use the freezer only if the pid is not 0 (a nonsense value) and the pid is not self.
+    // Freezing the current process is a fatal error.
+    bool useFreezer = freeze_ && (pid != 0) && (pid != sThisProcess);
     AutoMutex _l(lock_);
-    Timer t(pid, uid, timeout, extend_, freeze_, tracer_.getConfig(pid));
+    Timer t(pid, uid, timeout, extend_, useFreezer, tracer_.getConfig(pid));
     insertLocked(t);
     t.start();
     counters_.started++;