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

base/threading/platform_thread_linux.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 <sched.h>
 
 #include "base/lazy_instance.h"
@@ skipping 57 matching lines @@
   if (err < 0 && errno != EPERM)
     DPLOG(ERROR) << "prctl(PR_SET_NAME)";
 #endif  //  !defined(OS_NACL)
 }
 
 // static
 void PlatformThread::SetThreadPriority(PlatformThreadHandle handle,
                                        ThreadPriority priority) {
 #if !defined(OS_NACL)
   if (priority == kThreadPriority_RealtimeAudio) {
-    const struct sched_param kRealTimePrio = { 8 };
+    const struct sched_param kRealTimePrio = {8};
     if (pthread_setschedparam(pthread_self(), SCHED_RR, &kRealTimePrio) == 0) {
       // Got real time priority, no need to set nice level.
       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);
   const int kNiceSetting = ThreadNiceValue(priority);
-  if (setpriority(PRIO_PROCESS, handle.id_, kNiceSetting)) {
-    DVPLOG(1) << "Failed to set nice value of thread ("
-              << handle.id_ << ") to " << kNiceSetting;
+  const PlatformThreadId current_id = PlatformThread::CurrentId();
+  if (setpriority(PRIO_PROCESS,
+                  handle.id_ == current_id ? 0 : handle.id_,
+                  kNiceSetting)) {
+    DVPLOG(1) << "Failed to set nice value of thread (" << handle.id_ << ") to "
+              << kNiceSetting;
   }
 #endif  //  !defined(OS_NACL)
 }
 
 void InitThreading() {}
 
 void InitOnThread() {}
 
 void TerminateOnThread() {}
 
 size_t GetDefaultThreadStackSize(const pthread_attr_t& attributes) {
 #if !defined(THREAD_SANITIZER) && !defined(MEMORY_SANITIZER)
   return 0;
 #else
   // ThreadSanitizer bloats the stack heavily. Evidence has been that the
   // default stack size isn't enough for some browser tests.
   // MemorySanitizer needs this as a temporary fix for http://crbug.com/353687
   return 2 * (1 << 23);  // 2 times 8192K (the default stack size on Linux).
 #endif
 }
 
 }  // namespace base