Index: lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc =================================================================== --- lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc +++ lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc @@ -89,36 +89,50 @@ bool SuspendThread(SuspendedThreadID thread_id); }; -bool ThreadSuspender::SuspendThread(SuspendedThreadID thread_id) { +bool ThreadSuspender::SuspendThread(SuspendedThreadID tid) { // Are we already attached to this thread? // Currently this check takes linear time, however the number of threads is // usually small. - if (suspended_threads_list_.Contains(thread_id)) + if (suspended_threads_list_.Contains(tid)) return false; int pterrno; - if (internal_iserror(internal_ptrace(PTRACE_ATTACH, thread_id, NULL, NULL), + if (internal_iserror(internal_ptrace(PTRACE_ATTACH, tid, NULL, NULL), &pterrno)) { // Either the thread is dead, or something prevented us from attaching. // Log this event and move on. - VReport(1, "Could not attach to thread %d (errno %d).\n", thread_id, - pterrno); + VReport(1, "Could not attach to thread %d (errno %d).\n", tid, pterrno); return false; } else { - VReport(1, "Attached to thread %d.\n", thread_id); + VReport(1, "Attached to thread %d.\n", tid); // The thread is not guaranteed to stop before ptrace returns, so we must - // wait on it. - uptr waitpid_status; - HANDLE_EINTR(waitpid_status, internal_waitpid(thread_id, NULL, __WALL)); - int wperrno; - if (internal_iserror(waitpid_status, &wperrno)) { - // Got a ECHILD error. I don't think this situation is possible, but it - // doesn't hurt to report it. - VReport(1, "Waiting on thread %d failed, detaching (errno %d).\n", - thread_id, wperrno); - internal_ptrace(PTRACE_DETACH, thread_id, NULL, NULL); - return false; + // wait on it. Note: if the thread receives a signal concurrently, + // we can get notification about the signal before notification about stop. + // If such case we need to forward the signal to the thread, otherwise + // the signal will be missed (as we do PTRACE_DETACH with arg=0) and + // any logic relying on signals will break. After forwarding we need to + // continue to wait for stopping, because the thread is not stopped yet. + // We do ignore delivery of SIGSTOP, because we want to make stop-the-world + // as invisible as possible. + for (;;) { + int status; + uptr waitpid_status; + HANDLE_EINTR(waitpid_status, internal_waitpid(tid, &status, __WALL)); + int wperrno; + if (internal_iserror(waitpid_status, &wperrno)) { + // Got a ECHILD error. I don't think this situation is possible, but it + // doesn't hurt to report it. + VReport(1, "Waiting on thread %d failed, detaching (errno %d).\n", + tid, wperrno); + internal_ptrace(PTRACE_DETACH, tid, NULL, NULL); + return false; + } + if (WIFSTOPPED(status) && WSTOPSIG(status) != SIGSTOP) { + internal_ptrace(PTRACE_CONT, tid, 0, (void*)(uptr)WSTOPSIG(status)); + continue; + } + break; } - suspended_threads_list_.Append(thread_id); + suspended_threads_list_.Append(tid); return true; } } Index: test/tsan/signal_segv_handler.cc =================================================================== --- test/tsan/signal_segv_handler.cc +++ test/tsan/signal_segv_handler.cc @@ -24,9 +24,6 @@ } int main() { - // Disabled for now, because there is another issue in ptrace. - // It will be addressed in a subsequent change. - goto done; struct sigaction a; a.sa_sigaction = handler; a.sa_flags = SA_SIGINFO;