stability: fix shutdown synchronization with possibly pending/running probes

2 files changed, 19 insertions, 9 deletions

diff --git a/ChangeLog b/ChangeLog
index cf4f4611..20f5706a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2008-11-21  Frank Ch. Eigler  <fche@elastic.org>
+
+	* translate.cxx (emit_module_exit): Perform shutdown probe
+	synchronization after all unregistrations and end/error probe
+	runs.
+	
 2008-11-20  Frank Ch. Eigler  <fche@elastic.org>
 
 	PR 5689
diff --git a/translate.cxx b/translate.cxx
index 0d4cc266..8bae5275 100644
--- a/translate.cxx
+++ b/translate.cxx
@@ -1256,6 +1256,17 @@ c_unparser::emit_module_exit ()
   // while to abort right away.  Currently running probes are allowed to
   // terminate.  These may set STAP_SESSION_ERROR!
 
+  // We're processing the derived_probe_group list in reverse
+  // order.  This ensures that probes get unregistered in reverse
+  // order of the way they were registered.
+  vector<derived_probe_group*> g = all_session_groups (*session);
+  for (vector<derived_probe_group*>::reverse_iterator i = g.rbegin();
+       i != g.rend(); i++)
+    (*i)->emit_module_exit (*session); // NB: runs "end" probes
+
+  // But some other probes may have launched too during unregistration.
+  // Let's wait a while to make sure they're all done, done, done.
+
   // NB: systemtap_module_exit is assumed to be called from ordinary
   // user context, say during module unload.  Among other things, this
   // means we can sleep a while.
@@ -1266,20 +1277,13 @@ c_unparser::emit_module_exit ()
   o->newline(1) << "if (cpu_possible (i) && "
                 << "atomic_read (& ((struct context *)per_cpu_ptr(contexts, i))->busy)) "
                 << "holdon = 1;";
-  o->newline () << "schedule ();";
+  // NB: we run at least one of these during the shutdown sequence:
+  o->newline () << "yield ();"; // aka schedule() and then some 
   o->newline(-2) << "} while (holdon);";
 
   // XXX: might like to have an escape hatch, in case some probe is
   // genuinely stuck somehow
 
-  // Notice we're processing the derived_probe_group list in reverse
-  // order.  This ensures that probes get unregistered in reverse
-  // order of the way they were registered.
-  vector<derived_probe_group*> g = all_session_groups (*session);
-  for (vector<derived_probe_group*>::reverse_iterator i = g.rbegin();
-       i != g.rend(); i++)
-    (*i)->emit_module_exit (*session); // NB: runs "end" probes
-
   for (unsigned i=0; i<session->globals.size(); i++)
     {
       vardecl* v = session->globals[i];