tracepoint-unreg-sync.patch

commit 114add4208129cc08bc47175ad505c8b719fe942
Author: Yichun Zhang (agentzh) <yichun@openresty.com>
Date:   Fri Sep 16 13:37:38 2022 -0700

    Bug: runtime: we might not sync the tracepoint's SRCU state after unregistering the tracepoints
    
    It might lead to issues like PR29577.

diff --git a/tapsets.cxx b/tapsets.cxx
index 50b70aa58..cb4705ffa 100644
--- a/tapsets.cxx
+++ b/tapsets.cxx
@@ -12570,14 +12570,15 @@ tracepoint_derived_probe_group::emit_module_init (systemtap_session &s)
   s.op->newline(-1) << "}";
   s.op->newline(-1) << "}";
 
-  // This would be technically proper (on those autoconf-detectable
-  // kernels that include this function in tracepoint.h), however we
-  // already make several calls to synchronze_sched() during our
-  // shutdown processes.
+  // Modern kernels' tracepoint implementation makes use of SRCU and
+  // their tracepoint_synchronize_unregister() function calls
+  // synchronize_srcu(&tracepoint_srcu) right before calling synchronize_rcu().
+  // So it's safer to always call tracepoint_synchronize_unregister() to avoid
+  // any risks.
 
-  // s.op->newline() << "if (rc)";
-  // s.op->newline(1) << "tracepoint_synchronize_unregister();";
-  // s.op->indent(-1);
+  s.op->newline() << "if (rc)";
+  s.op->newline(1) << "tracepoint_synchronize_unregister();";
+  s.op->indent(-1);
 }
 
 
@@ -12592,9 +12593,8 @@ tracepoint_derived_probe_group::emit_module_exit (systemtap_session& s)
   s.op->newline(1) << "stap_tracepoint_probes[i].unreg();";
   s.op->indent(-1);
 
-  // Not necessary: see above.
-
-  // s.op->newline() << "tracepoint_synchronize_unregister();";
+  // This is necessary: see above.
+  s.op->newline() << "tracepoint_synchronize_unregister();";
 }