[Lldb-commits] [lldb] r266733 - LLDB: Fixed two race conditions when stopping private state thread

[Marianne Mailhot-Sarrasin via lldb-commits]

Author: mamai
Date: Tue Apr 19 08:21:46 2016
New Revision: 266733

URL: http://llvm.org/viewvc/llvm-project?rev=266733&view=rev
Log:
LLDB: Fixed two race conditions when stopping private state thread

When stopping the private state thread, there was a race condition between the time the thread exits (resetting the HostThread object) and the time a Join was attempted, especially in the case of a timeout.

The previous workaround of copying the HostThread object is not enough, since on a Reset the internal thread stuff gets nulled out regardless of which HostThread object actually has Reset called on it, resulting in an attempt to dereference a null pointer on the subsequent call to Join from the copy as well.

Additionally, there was a race between the detach (called when stopping the process) and the stop itself, causing the stop to time out because it was waiting for the private state thread to see the stop state, but it had exited immediately after entering the detached state.

Patch by cameron314

Differential Revision: http://reviews.llvm.org/D19122

Modified:
    lldb/trunk/include/lldb/Target/Process.h
    lldb/trunk/source/Target/Process.cpp

Modified: lldb/trunk/include/lldb/Target/Process.h
URL: http://llvm.org/viewvc/llvm-project/lldb/trunk/include/lldb/Target/Process.h?rev=266733&r1=266732&r2=266733&view=diff
==============================================================================
--- lldb/trunk/include/lldb/Target/Process.h (original)
+++ lldb/trunk/include/lldb/Target/Process.h Tue Apr 19 08:21:46 2016
@@ -3310,7 +3310,10 @@ protected:
     bool
     PrivateStateThreadIsValid () const
     {
-        return m_private_state_thread.IsJoinable();
+        lldb::StateType state = m_private_state.GetValue();
+        return state != lldb::eStateDetached &&
+               state != lldb::eStateExited &&
+               m_private_state_thread.IsJoinable();
     }
     
     void

Modified: lldb/trunk/source/Target/Process.cpp
URL: http://llvm.org/viewvc/llvm-project/lldb/trunk/source/Target/Process.cpp?rev=266733&r1=266732&r2=266733&view=diff
==============================================================================
--- lldb/trunk/source/Target/Process.cpp (original)
+++ lldb/trunk/source/Target/Process.cpp Tue Apr 19 08:21:46 2016
@@ -4112,11 +4112,8 @@ Process::ControlPrivateStateThread (uint
     if (log)
         log->Printf ("Process::%s (signal = %d)", __FUNCTION__, signal);
 
-    // Signal the private state thread. First we should copy this is case the
-    // thread starts exiting since the private state thread will NULL this out
-    // when it exits
-    HostThread private_state_thread(m_private_state_thread);
-    if (private_state_thread.IsJoinable())
+    // Signal the private state thread
+    if (PrivateStateThreadIsValid())
     {
         TimeValue timeout_time;
         bool timed_out;
@@ -4134,7 +4131,7 @@ Process::ControlPrivateStateThread (uint
         {
             if (timed_out)
             {
-                Error error = private_state_thread.Cancel();
+                Error error = m_private_state_thread.Cancel();
                 if (log)
                     log->Printf ("Timed out responding to the control event, cancel got error: \"%s\".", error.AsCString());
             }
@@ -4145,7 +4142,7 @@ Process::ControlPrivateStateThread (uint
             }
 
             thread_result_t result = NULL;
-            private_state_thread.Join(&result);
+            m_private_state_thread.Join(&result);
             m_private_state_thread.Reset();
         }
     }
@@ -4449,7 +4446,6 @@ Process::RunPrivateStateThread (bool is_
     if (!is_secondary_thread)
         m_public_run_lock.SetStopped();
     m_private_state_control_wait.SetValue (true, eBroadcastAlways);
-    m_private_state_thread.Reset();
     return NULL;
 }