From d9a06afb19156b61ee85c975a292d884bba09c7f Mon Sep 17 00:00:00 2001 From: Christopher Ferris Date: Thu, 3 Sep 2015 11:25:55 -0700 Subject: [PATCH] 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 d7226f9a1485ba19f714369fd7f8b444d66feb61) Change-Id: Ib990a06733cc93717752ab4998f4ae26afd7e249 --- libbacktrace/BacktraceCurrent.cpp | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/libbacktrace/BacktraceCurrent.cpp b/libbacktrace/BacktraceCurrent.cpp index 2714d93df..d33955093 100644 --- a/libbacktrace/BacktraceCurrent.cpp +++ b/libbacktrace/BacktraceCurrent.cpp @@ -93,6 +93,10 @@ bool BacktraceCurrent::DiscardFrame(const backtrace_frame_data_t& frame) { 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) { ThreadEntry* entry = ThreadEntry::Get(getpid(), gettid(), false); 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. 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 // continue. - sigaction(THREAD_SIGNAL, &oldact, nullptr); pthread_mutex_unlock(&g_sigaction_mutex); bool unwind_done = false;