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Commit 7a67c335 authored by Christopher Ferris's avatar Christopher Ferris Committed by Gerrit Code Review
Browse files

Merge "Modify the code to avoid potential deadlocks."

parents ce817c38 2d091717

libbacktrace/BacktraceCurrent.cpp

+28 −12
Original line number Diff line number Diff line
@@ -96,7 +96,7 @@ static pthread_mutex_t g_sigaction_mutex = PTHREAD_MUTEX_INITIALIZER; 
static void SignalHandler(int, siginfo_t*, void* sigcontext) {

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

  if (!entry) {

    BACK_LOGW("Unable to find pid %d tid %d information", getpid(), gettid());

    BACK_LOGE("pid %d, tid %d entry not found", getpid(), gettid());

    return;

  }
@@ -109,9 +109,14 @@ static void SignalHandler(int, siginfo_t*, void* sigcontext) { 
  // the thread run ahead causing problems.

  // The number indicates that we are waiting for the second Wake() call

  // overall which is made by the thread requesting an unwind.

  entry->Wait(2);



  ThreadEntry::Remove(entry);

  if (entry->Wait(2)) {

    // Do not remove the entry here because that can result in a deadlock

    // if the code cannot properly send a signal to the thread under test.

    entry->Wake();

  } else {

    // At this point, it is possible that entry has been freed, so just exit.

    BACK_LOGE("Timed out waiting for unwind thread to indicate it completed.");

  }

}



bool BacktraceCurrent::UnwindThread(size_t num_ignore_frames) {
@@ -128,17 +133,15 @@ bool BacktraceCurrent::UnwindThread(size_t num_ignore_frames) { 
  act.sa_flags = SA_RESTART | SA_SIGINFO | SA_ONSTACK;

  sigemptyset(&act.sa_mask);

  if (sigaction(THREAD_SIGNAL, &act, &oldact) != 0) {

    BACK_LOGW("sigaction failed %s", strerror(errno));

    entry->Unlock();

    BACK_LOGE("sigaction failed: %s", strerror(errno));

    ThreadEntry::Remove(entry);

    pthread_mutex_unlock(&g_sigaction_mutex);

    return false;

  }



  if (tgkill(Pid(), Tid(), THREAD_SIGNAL) != 0) {

    BACK_LOGW("tgkill %d failed: %s", Tid(), strerror(errno));

    BACK_LOGE("tgkill %d failed: %s", Tid(), strerror(errno));

    sigaction(THREAD_SIGNAL, &oldact, nullptr);

    entry->Unlock();

    ThreadEntry::Remove(entry);

    pthread_mutex_unlock(&g_sigaction_mutex);

    return false;
@@ -146,17 +149,30 @@ bool BacktraceCurrent::UnwindThread(size_t num_ignore_frames) { 


  // Wait for the thread to get the ucontext. The number indicates

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

  entry->Wait(1);

  bool wait_completed = entry->Wait(1);



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

  // continue.

  sigaction(THREAD_SIGNAL, &oldact, nullptr);

  pthread_mutex_unlock(&g_sigaction_mutex);



  bool unwind_done = UnwindFromContext(num_ignore_frames, entry->GetUcontext());

  bool unwind_done = false;

  if (wait_completed) {

    unwind_done = UnwindFromContext(num_ignore_frames, entry->GetUcontext());



    // Tell the signal handler to exit and release the entry.

    entry->Wake();



    // Wait for the thread to indicate it is done with the ThreadEntry.

    if (!entry->Wait(3)) {

      // Send a warning, but do not mark as a failure to unwind.

      BACK_LOGW("Timed out waiting for signal handler to indicate it finished.");

    }

  } else {

    BACK_LOGE("Timed out waiting for signal handler to get ucontext data.");

  }



  ThreadEntry::Remove(entry);



  return unwind_done;

}

libbacktrace/BacktraceLog.h

+3 −0
Original line number Diff line number Diff line
@@ -25,4 +25,7 @@ 
#define BACK_LOGW(format, ...) \

  ALOGW("%s: " format, __PRETTY_FUNCTION__, ##__VA_ARGS__)



#define BACK_LOGE(format, ...) \

  ALOGE("%s: " format, __PRETTY_FUNCTION__, ##__VA_ARGS__)



#endif // _LIBBACKTRACE_BACKTRACE_LOG_H

libbacktrace/ThreadEntry.cpp

+8 −4
Original line number Diff line number Diff line
@@ -69,7 +69,7 @@ ThreadEntry* ThreadEntry::Get(pid_t pid, pid_t tid, bool create) { 
}



void ThreadEntry::Remove(ThreadEntry* entry) {

  pthread_mutex_unlock(&entry->mutex_);

  entry->Unlock();



  pthread_mutex_lock(&ThreadEntry::list_mutex_);

  if (--entry->ref_count_ == 0) {
@@ -96,20 +96,24 @@ ThreadEntry::~ThreadEntry() { 
  pthread_cond_destroy(&wait_cond_);

}



void ThreadEntry::Wait(int value) {

bool ThreadEntry::Wait(int value) {

  timespec ts;

  clock_gettime(CLOCK_MONOTONIC, &ts);

  ts.tv_sec += 10;

  ts.tv_sec += 5;



  bool wait_completed = true;

  pthread_mutex_lock(&wait_mutex_);

  while (wait_value_ != value) {

    int ret = pthread_cond_timedwait(&wait_cond_, &wait_mutex_, &ts);

    if (ret != 0) {

      BACK_LOGW("pthread_cond_timedwait failed: %s", strerror(ret));

      BACK_LOGW("pthread_cond_timedwait for value %d failed: %s", value, strerror(ret));

      wait_completed = false;

      break;

    }

  }

  pthread_mutex_unlock(&wait_mutex_);



  return wait_completed;

}



void ThreadEntry::Wake() {

libbacktrace/ThreadEntry.h

+1 −1
Original line number Diff line number Diff line
@@ -29,7 +29,7 @@ public: 


  void Wake();



  void Wait(int);

  bool Wait(int);



  void CopyUcontextFromSigcontext(void*);