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Commit d9a06afb authored by Christopher Ferris's avatar Christopher Ferris
Browse files

Add a logging handler on timeout. 

If the signal handler doesn't fire in the given time when trying to unwind
a thread, put on a logging handler. This prevents crashes if the signal
does eventually fire.

Bug: 23783762

(cherry picked from commit d7226f9a)

Change-Id: Ib990a06733cc93717752ab4998f4ae26afd7e249
parent bc8c731a

libbacktrace/BacktraceCurrent.cpp

+17 −1
Original line number Original line Diff line number Diff line
@@ -93,6 +93,10 @@ bool BacktraceCurrent::DiscardFrame(const backtrace_frame_data_t& frame) { 




static pthread_mutex_t g_sigaction_mutex = PTHREAD_MUTEX_INITIALIZER;

static pthread_mutex_t g_sigaction_mutex = PTHREAD_MUTEX_INITIALIZER;





static void SignalLogOnly(int, siginfo_t*, void*) {

  BACK_LOGE("pid %d, tid %d: Received a spurious signal %d\n", getpid(), gettid(), THREAD_SIGNAL);

}



static void SignalHandler(int, siginfo_t*, void* sigcontext) {

static void SignalHandler(int, siginfo_t*, void* sigcontext) {

  ThreadEntry* entry = ThreadEntry::Get(getpid(), gettid(), false);

  ThreadEntry* entry = ThreadEntry::Get(getpid(), gettid(), false);

  if (!entry) {

  if (!entry) {
@@ -151,9 +155,21 @@ bool BacktraceCurrent::UnwindThread(size_t num_ignore_frames) { 
  // that we are waiting for the first Wake() call made by the thread.

  // that we are waiting for the first Wake() call made by the thread.

  bool wait_completed = entry->Wait(1);

  bool wait_completed = entry->Wait(1);





  if (!wait_completed && oldact.sa_sigaction == nullptr) {

    // If the wait failed, it could be that the signal could not be delivered

    // within the timeout. Add a signal handler that's simply going to log

    // something so that we don't crash if the signal eventually gets

    // delivered. Only do this if there isn't already an action set up.

    memset(&act, 0, sizeof(act));

    act.sa_sigaction = SignalLogOnly;

    act.sa_flags = SA_RESTART | SA_SIGINFO | SA_ONSTACK;

    sigemptyset(&act.sa_mask);

    sigaction(THREAD_SIGNAL, &act, nullptr);

  } else {

    sigaction(THREAD_SIGNAL, &oldact, nullptr);

  }

  // After the thread has received the signal, allow other unwinders to

  // After the thread has received the signal, allow other unwinders to

  // continue.

  // continue.

  sigaction(THREAD_SIGNAL, &oldact, nullptr);

  pthread_mutex_unlock(&g_sigaction_mutex);

  pthread_mutex_unlock(&g_sigaction_mutex);





  bool unwind_done = false;

  bool unwind_done = false;