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