simpleperf: write -1 to perf_event_paranoid when running as root.

The monitored threads may create child processes not running as root.
This patch is to make sure they have permission to create inherited
tracepoint events.

Bug: http://b/62230699
Test: run simpleperf manually on device.
Change-Id: I02798c834f8a0500057e4e1c70291cfb05c3f92d

diff --git a/simpleperf/environment.cpp b/simpleperf/environment.cpp
index d0cb835..7fff85f 100644 (file)
--- a/simpleperf/environment.cpp
+++ b/simpleperf/environment.cpp
@@ -361,8 +361,11 @@ static const char* GetLimitLevelDescription(int limit_level) {
 }
 
 bool CheckPerfEventLimit() {
-  // root is not limited by /proc/sys/kernel/perf_event_paranoid.
-  if (IsRoot()) {
+  // Root is not limited by /proc/sys/kernel/perf_event_paranoid. However, the monitored threads
+  // may create child processes not running as root. To make sure the child processes have
+  // enough permission to create inherited tracepoint events, write -1 to perf_event_paranoid.
+  // See http://b/62230699.
+  if (IsRoot() && android::base::WriteStringToFile("-1", "/proc/sys/kernel/perf_event_paranoid")) {
     return true;
   }
   int limit_level;