Linux, Android: fix call to setpriority(2).

base/threading/platform_thread_android.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/threading/platform_thread.h"
 
 #include <errno.h>
 #include <sys/prctl.h>
 #include <sys/resource.h>
 
@@ skipping 47 matching lines @@
 void PlatformThread::SetThreadPriority(PlatformThreadHandle handle,
                                        ThreadPriority priority) {
   // On Android, we set the Audio priority through JNI as Audio priority
   // will also allow the process to run while it is backgrounded.
   if (priority == kThreadPriority_RealtimeAudio) {
     JNIEnv* env = base::android::AttachCurrentThread();
     Java_ThreadUtils_setThreadPriorityAudio(env, PlatformThread::CurrentId());
     return;
   }
 
-  // setpriority(2) will set a thread's priority if it is passed a tid as
-  // the 'process identifier', not affecting the rest of the threads in the
-  // process. Setting this priority will only succeed if the user has been
-  // granted permission to adjust nice values on the system.
+  // setpriority(2) should change the whole thread group's (i.e. process)
+  // priority. however, on linux it will only change the target thread's
+  // priority. see the bugs section in
+  // http://man7.org/linux/man-pages/man2/getpriority.2.html.
+  // we prefer using 0 rather than the current thread id since they are
+  // equivalent but it makes sandboxing easier (https://crbug.com/399473).
   DCHECK_NE(handle.id_, kInvalidThreadId);
   int kNiceSetting = ThreadNiceValue(priority);
-  if (setpriority(PRIO_PROCESS, handle.id_, kNiceSetting))
+  const PlatformThreadId current_id = PlatformThread::CurrentId();
+  if (setpriority(PRIO_PROCESS,
+                  handle.id_ == current_id ? 0 : handle.id_,
+                  kNiceSetting)) {
     LOG(ERROR) << "Failed to set nice value of thread to " << kNiceSetting;
+  }
 }
 
 void PlatformThread::SetName(const char* name) {
   ThreadIdNameManager::GetInstance()->SetName(CurrentId(), name);
   tracked_objects::ThreadData::InitializeThreadContext(name);
 
   // Like linux, on android we can get the thread names to show up in the
   // debugger by setting the process name for the LWP.
   // We don't want to do this for the main thread because that would rename
   // the process, causing tools like killall to stop working.
@@ skipping 29 matching lines @@
   // 1Mb is not enough for some tests (see http://crbug.com/263749 for example).
   return 2 * (1 << 20);  // 2Mb
 #endif
 }
 
 bool RegisterThreadUtils(JNIEnv* env) {
   return RegisterNativesImpl(env);
 }
 
 }  // namespace base