sandbox/linux/services/thread_helpers.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "sandbox/linux/services/thread_helpers.h"
   6
   7 #include <errno.h>
   8 #include <fcntl.h>
   9 #include <signal.h>
  10 #include <sys/types.h>
  11 #include <sys/stat.h>
  12 #include <unistd.h>
  13
  14 #include <string>
  15
  16 #include "base/basictypes.h"
  17 #include "base/bind.h"
  18 #include "base/callback.h"
  19 #include "base/files/scoped_file.h"
  20 #include "base/logging.h"
  21 #include "base/posix/eintr_wrapper.h"
  22 #include "base/strings/string_number_conversions.h"
  23 #include "base/threading/platform_thread.h"
  24 #include "base/threading/thread.h"
  25 #include "sandbox/linux/services/proc_util.h"
  26
  27 namespace sandbox {
  28
  29 namespace {
  30
  31 const char kAssertSingleThreadedError[] =
  32     "Current process is not mono-threaded!";
  33
  34 bool IsSingleThreadedImpl(int proc_fd) {
  35   CHECK_LE(0, proc_fd);
  36   struct stat task_stat;
  37   int fstat_ret = fstatat(proc_fd, "self/task/", &task_stat, 0);
  38   PCHECK(0 == fstat_ret);
  39
  40   // At least "..", "." and the current thread should be present.
  41   CHECK_LE(3UL, task_stat.st_nlink);
  42   // Counting threads via /proc/self/task could be racy. For the purpose of
  43   // determining if the current proces is monothreaded it works: if at any
  44   // time it becomes monothreaded, it'll stay so.
  45   return task_stat.st_nlink == 3;
  46 }
  47
  48 bool IsThreadPresentInProcFS(int proc_fd,
  49                              const std::string& thread_id_dir_str) {
  50   struct stat task_stat;
  51   const int fstat_ret =
  52       fstatat(proc_fd, thread_id_dir_str.c_str(), &task_stat, 0);
  53   if (fstat_ret < 0) {
  54     PCHECK(ENOENT == errno);
  55     return false;
  56   }
  57   return true;
  58 }
  59
  60 // Run |cb| in a loop until it returns false. Every time |cb| runs, sleep
  61 // for an exponentially increasing amount of time. |cb| is expected to return
  62 // false very quickly and this will crash if it doesn't happen within ~64ms on
  63 // Debug builds (2s on Release builds).
  64 // This is guaranteed to not sleep more than twice as much as the bare minimum
  65 // amount of time.
  66 void RunWhileTrue(const base::Callback<bool(void)>& cb) {
  67 #if defined(NDEBUG)
  68   // In Release mode, crash after 30 iterations, which means having spent
  69   // roughly 2s in
  70   // nanosleep(2) cumulatively.
  71   const unsigned int kMaxIterations = 30U;
  72 #else
  73   // In practice, this never goes through more than a couple iterations. In
  74   // debug mode, crash after 64ms (+ eventually 25 times the granularity of
  75   // the clock) in nanosleep(2). This ensures that this is not becoming too
  76   // slow.
  77   const unsigned int kMaxIterations = 25U;
  78 #endif
  79
  80   // Run |cb| with an exponential back-off, sleeping 2^iterations nanoseconds
  81   // in nanosleep(2).
  82   // Note: the clock may not allow for nanosecond granularity, in this case the
  83   // first iterations would sleep a tiny bit more instead, which would not
  84   // change the calculations significantly.
  85   for (unsigned int i = 0; i < kMaxIterations; ++i) {
  86     if (!cb.Run()) {
  87       return;
  88     }
  89
  90     // Increase the waiting time exponentially.
  91     struct timespec ts = {0, 1L << i /* nanoseconds */};
  92     PCHECK(0 == HANDLE_EINTR(nanosleep(&ts, &ts)));
  93   }
  94
  95   LOG(FATAL) << kAssertSingleThreadedError << " (iterations: " << kMaxIterations
  96              << ")";
  97
  98   NOTREACHED();
  99 }
 100
 101 bool IsMultiThreaded(int proc_fd) {
 102   return !ThreadHelpers::IsSingleThreaded(proc_fd);
 103 }
 104
 105 }  // namespace
 106
 107 // static
 108 bool ThreadHelpers::IsSingleThreaded(int proc_fd) {
 109   DCHECK_LE(0, proc_fd);
 110   return IsSingleThreadedImpl(proc_fd);
 111 }
 112
 113 // static
 114 bool ThreadHelpers::IsSingleThreaded() {
 115   base::ScopedFD task_fd(ProcUtil::OpenProc());
 116   return IsSingleThreaded(task_fd.get());
 117 }
 118
 119 // static
 120 void ThreadHelpers::AssertSingleThreaded(int proc_fd) {
 121   DCHECK_LE(0, proc_fd);
 122   const base::Callback<bool(void)> cb = base::Bind(&IsMultiThreaded, proc_fd);
 123   RunWhileTrue(cb);
 124 }
 125
 126 void ThreadHelpers::AssertSingleThreaded() {
 127   base::ScopedFD task_fd(ProcUtil::OpenProc());
 128   AssertSingleThreaded(task_fd.get());
 129 }
 130
 131 // static
 132 bool ThreadHelpers::StopThreadAndWatchProcFS(int proc_fd,
 133                                              base::Thread* thread) {
 134   DCHECK_LE(0, proc_fd);
 135   DCHECK(thread);
 136   const base::PlatformThreadId thread_id = thread->thread_id();
 137   const std::string thread_id_dir_str =
 138       "self/task/" + base::IntToString(thread_id) + "/";
 139
 140   // The kernel is at liberty to wake the thread id futex before updating
 141   // /proc. Following Stop(), the thread is joined, but entries in /proc may
 142   // not have been updated.
 143   thread->Stop();
 144
 145   const base::Callback<bool(void)> cb =
 146       base::Bind(&IsThreadPresentInProcFS, proc_fd, thread_id_dir_str);
 147
 148   RunWhileTrue(cb);
 149
 150   return true;
 151 }
 152
 153 // static
 154 const char* ThreadHelpers::GetAssertSingleThreadedErrorMessageForTests() {
 155   return kAssertSingleThreadedError;
 156 }
 157
 158 }  // namespace sandbox