src: fix race condition in ~NodeTraceBuffer

Libuv does not guarantee that handles have their close
callbacks called in the order in which they were added
(and in fact, currently calls them in reverse order).

This patch ensures that the `flush_signal_` handle
is no longer in use (i.e. its close callback has already
been run) when we signal to the main thread that
`~NodeTraceBuffer` may be destroyed.

The same applies for `~NodeTraceWriter`.

Credit for debugging goes to Gireesh Punathil.

Fixes: #25512
Co-authored-by: Gireesh Punathil <gpunathi@in.ibm.com>

PR-URL: #25896
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Eugene Ostroukhov <eostroukhov@google.com>

Author: addaleax

src/tracing/node_trace_buffer.cc

@@ -1,4 +1,5 @@
 #include "tracing/node_trace_buffer.h"
+#include "util-inl.h"
 
 namespace node {
 namespace tracing {
@@ -170,15 +171,25 @@ void NodeTraceBuffer::NonBlockingFlushSignalCb(uv_async_t* signal) {
 
 // static
 void NodeTraceBuffer::ExitSignalCb(uv_async_t* signal) {
-  NodeTraceBuffer* buffer = reinterpret_cast<NodeTraceBuffer*>(signal->data);
-  uv_close(reinterpret_cast<uv_handle_t*>(&buffer->flush_signal_), nullptr);
-  uv_close(reinterpret_cast<uv_handle_t*>(&buffer->exit_signal_),
+  NodeTraceBuffer* buffer =
+      ContainerOf(&NodeTraceBuffer::exit_signal_, signal);
+
+  // Close both flush_signal_ and exit_signal_.
+  uv_close(reinterpret_cast<uv_handle_t*>(&buffer->flush_signal_),
            [](uv_handle_t* signal) {
+    NodeTraceBuffer* buffer =
+        ContainerOf(&NodeTraceBuffer::flush_signal_,
+                    reinterpret_cast<uv_async_t*>(signal));
+
+    uv_close(reinterpret_cast<uv_handle_t*>(&buffer->exit_signal_),
+             [](uv_handle_t* signal) {
       NodeTraceBuffer* buffer =
-          reinterpret_cast<NodeTraceBuffer*>(signal->data);
-      Mutex::ScopedLock scoped_lock(buffer->exit_mutex_);
-      buffer->exited_ = true;
-      buffer->exit_cond_.Signal(scoped_lock);
+          ContainerOf(&NodeTraceBuffer::exit_signal_,
+                      reinterpret_cast<uv_async_t*>(signal));
+        Mutex::ScopedLock scoped_lock(buffer->exit_mutex_);
+        buffer->exited_ = true;
+        buffer->exit_cond_.Signal(scoped_lock);
+    });
   });
 }
 

src/tracing/node_trace_writer.cc

@@ -218,18 +218,23 @@ void NodeTraceWriter::AfterWrite() {
 void NodeTraceWriter::ExitSignalCb(uv_async_t* signal) {
   NodeTraceWriter* trace_writer =
       ContainerOf(&NodeTraceWriter::exit_signal_, signal);
+  // Close both flush_signal_ and exit_signal_.
   uv_close(reinterpret_cast<uv_handle_t*>(&trace_writer->flush_signal_),
-           nullptr);
-  uv_close(reinterpret_cast<uv_handle_t*>(&trace_writer->exit_signal_),
            [](uv_handle_t* signal) {
-      NodeTraceWriter* trace_writer =
-          ContainerOf(&NodeTraceWriter::exit_signal_,
-                      reinterpret_cast<uv_async_t*>(signal));
-      Mutex::ScopedLock scoped_lock(trace_writer->request_mutex_);
-      trace_writer->exited_ = true;
-      trace_writer->exit_cond_.Signal(scoped_lock);
-  });
+             NodeTraceWriter* trace_writer =
+                 ContainerOf(&NodeTraceWriter::flush_signal_,
+                             reinterpret_cast<uv_async_t*>(signal));
+             uv_close(
+                 reinterpret_cast<uv_handle_t*>(&trace_writer->exit_signal_),
+                 [](uv_handle_t* signal) {
+                   NodeTraceWriter* trace_writer =
+                       ContainerOf(&NodeTraceWriter::exit_signal_,
+                                   reinterpret_cast<uv_async_t*>(signal));
+                   Mutex::ScopedLock scoped_lock(trace_writer->request_mutex_);
+                   trace_writer->exited_ = true;
+                   trace_writer->exit_cond_.Signal(scoped_lock);
+                 });
+           });
 }
-
 }  // namespace tracing
 }  // namespace node