commit 38f01e05ef7f7ef18a43339436fba645d123b838
author Elliott Hughes <enh@google.com> Fri Oct 27 15:28:54 2017 -0700
committer Elliott Hughes <enh@google.com> Fri Oct 27 15:40:15 2017 -0700
tree e6dbb0977a34d052056e935d86bd3cdcc9473188
parent dfece7a3ee1b8a11abea3f55bf44df21ebc4bc79

Preserve historical pthread_create scheduler behavior better.

At the cost of two flag bits for what POSIX thinks should be a boolean
choice, plus somewhat confusing behavior from pthread_attr_getinheritsched
depending on when you call it/what specific scheduler attributes you've
set in the pthread_attr_t, we can emulate the old behavior exactly and
prevent annoying SELinux denial spam caused by calls to sched_setscheduler.

Bug: http://b/68391226
Test: adb logcat on boot contains no sys_nice avc denials
Change-Id: I4f759c2c4fd1d80cceb0912d7da09d35902e2e5e

libc/bionic/pthread_create.cpp

diff --git a/libc/bionic/pthread_create.cpp b/libc/bionic/pthread_create.cpp
index 40db785..21a707b 100644
--- a/libc/bionic/pthread_create.cpp
+++ b/libc/bionic/pthread_create.cpp
@@ -122,7 +122,7 @@
   bool need_set = true;
   int policy;
   sched_param param;
-  if (thread->attr.flags & PTHREAD_ATTR_FLAG_INHERIT) {
+  if ((thread->attr.flags & PTHREAD_ATTR_FLAG_INHERIT) != 0) {
     // Unless the parent has SCHED_RESET_ON_FORK set, we've already inherited from the parent.
     policy = sched_getscheduler(0);
     need_set = ((policy & SCHED_RESET_ON_FORK) != 0);
@@ -142,6 +142,11 @@
     policy = thread->attr.sched_policy;
     param.sched_priority = thread->attr.sched_priority;
   }
+  // Backwards compatibility: before P, Android didn't have pthread_attr_setinheritsched,
+  // and our behavior was neither of the POSIX behaviors.
+  if ((thread->attr.flags & (PTHREAD_ATTR_FLAG_INHERIT|PTHREAD_ATTR_FLAG_EXPLICIT)) == 0) {
+    need_set = (thread->attr.sched_policy != SCHED_NORMAL);
+  }
   if (need_set) {
     if (sched_setscheduler(thread->tid, policy, &param) == -1) {
       async_safe_format_log(ANDROID_LOG_WARN, "libc",