[NativeProcessLinux] Fix potential race during thread exit

[labath]

Summary

This is the same issue as we had in D9145 for thread creation. Going through the full
ThreadDidStop/RequestResume cycle can cause a deferred notification to fire, which is not correct
when we are ignoring an event and resuming the thread. In this case it doesn't matter much since
the thread will die after that anyway, but for correctness, we should do the same thing here.
Also treating the SIGTRAP case the same way.

[ovyalov]

LGTM

lldb/trunk/source/Plugins/Process/Linux/NativeProcessLinux.cpp

case (SIGTRAP | (PTRACE_EVENT_EXEC << 8)):
         StopRunningThreads (pid);
 
         break;
     }
 
     case (SIGTRAP | (PTRACE_EVENT_EXIT << 8)):
     {
         // The inferior process or one of its threads is about to exit.
-        if (! thread_sp)
-            break;
-
-        // This thread is currently stopped.  It's not actually dead yet, just about to be.
-        ThreadDidStop (pid, false);
-        // The actual stop reason does not matter much, as we are going to resume the thread a
-        // few lines down. If we ever want to report this state to the debugger, then we should
-        // invent a new stop reason.
-        std::static_pointer_cast<NativeThreadLinux>(thread_sp)->SetStoppedBySignal(LLDB_INVALID_SIGNAL_NUMBER);
+        // We don't want to do anything with the thread so we just resume it. In case we
+        // want to implement "break on thread exit" functionality, we would need to stop
+        // here.
 
         unsigned long data = 0;
         if (GetEventMessage(pid, &data).Fail())
             data = -1;
 
         if (log)
         {
             log->Printf ("NativeProcessLinux::%s() received PTRACE_EVENT_EXIT, data = %lx (WIFEXITED=%s,WIFSIGNALED=%s), pid = %" PRIu64 " (%s)",
                          __FUNCTION__,
                          data, WIFEXITED (data) ? "true" : "false", WIFSIGNALED (data) ? "true" : "false",
                          pid,
                     is_main_thread ? "is main thread" : "not main thread");
         }
 
         if (is_main_thread)
         {
             SetExitStatus (convert_pid_status_to_exit_type (data), convert_pid_status_to_return_code (data), nullptr, true);
         }
 
-        const int signo = static_cast<int> (data);
-        ResumeThread(pid,
-                [=](lldb::tid_t tid_to_resume, bool supress_signal)
-                {
-                    std::static_pointer_cast<NativeThreadLinux> (thread_sp)->SetRunning ();
-                    return Resume (tid_to_resume, (supress_signal) ? LLDB_INVALID_SIGNAL_NUMBER : signo);
-                },
-                true);
+        Resume(pid, LLDB_INVALID_SIGNAL_NUMBER);
 
         break;
     }
 
     case 0:
     case TRAP_TRACE:  // We receive this on single stepping.
     case TRAP_HWBKPT: // We receive this on watchpoint hit
         if (thread_sp)
case TRAP_BRKPT:
         MonitorBreakpoint(pid, thread_sp);
         break;
 
     case SIGTRAP:
     case (SIGTRAP | 0x80):
         if (log)
             log->Printf ("NativeProcessLinux::%s() received unknown SIGTRAP system call stop event, pid %" PRIu64 "tid %" PRIu64 ", resuming", __FUNCTION__, GetID (), pid);
 
-        // This thread is currently stopped.
-        ThreadDidStop (pid, false);
-        if (thread_sp)
-            std::static_pointer_cast<NativeThreadLinux> (thread_sp)->SetStoppedBySignal (SIGTRAP);
-
-            
         // Ignore these signals until we know more about them.
-        ResumeThread(pid,
-                [=](lldb::tid_t tid_to_resume, bool supress_signal)
-                {
-                    std::static_pointer_cast<NativeThreadLinux> (thread_sp)->SetRunning ();
-                    return Resume (tid_to_resume, LLDB_INVALID_SIGNAL_NUMBER);
-                },
-                true);
+        Resume(pid, LLDB_INVALID_SIGNAL_NUMBER);
         break;
 
     default:
         assert(false && "Unexpected SIGTRAP code!");
         if (log)
-            log->Printf ("NativeProcessLinux::%s() pid %" PRIu64 "tid %" PRIu64 " received unhandled SIGTRAP code: 0x%" PRIx64, __FUNCTION__, GetID (), pid, static_cast<uint64_t> (SIGTRAP | (PTRACE_EVENT_CLONE << 8)));
+            log->Printf ("NativeProcessLinux::%s() pid %" PRIu64 "tid %" PRIu64 " received unhandled SIGTRAP code: 0x%d",
+                    __FUNCTION__, GetID (), pid, info->si_code);
         break;
         
     }
 }
 
 void
 NativeProcessLinux::MonitorTrace(lldb::pid_t pid, NativeThreadProtocolSP thread_sp)
 {