From 91bf355bb7931df2c61902d36f55d266b219c96a Mon Sep 17 00:00:00 2001
From: Remi Gacogne <remi.gacogne@powerdns.com>
Date: Fri, 9 Dec 2022 16:58:15 +0100
Subject: [PATCH] dnsdist: Add TSAN annotations in the channel code

So Thread Sanitizer knows that the object we are passing is no longer
used in the sender, and will now be used in the receiver (happens-before).
---
 pdns/channel.hh | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/pdns/channel.hh b/pdns/channel.hh
index fd82ca1970..b13b3f9881 100644
--- a/pdns/channel.hh
+++ b/pdns/channel.hh
@@ -25,6 +25,20 @@
 
 #include "misc.hh"
 
+/* g++ defines __SANITIZE_THREAD__
+   clang++ supports the nice __has_feature(thread_sanitizer),
+   let's merge them */
+#if defined(__has_feature)
+#if __has_feature(thread_sanitizer)
+#define __SANITIZE_THREAD__ 1
+#endif
+#endif
+
+#if __SANITIZE_THREAD__
+extern "C" void __tsan_acquire(void *addr);
+extern "C" void __tsan_release(void *addr);
+#endif
+
 namespace pdns
 {
 namespace channel
@@ -210,6 +224,9 @@ namespace channel
     auto ptr = object.get();
     static_assert(sizeof(ptr) <= PIPE_BUF, "Writes up to PIPE_BUF are guaranted not to interleaved and to either fully succeed or fail");
     while (true) {
+#if __SANITIZE_THREAD__
+      __tsan_release(ptr);
+#endif /* __SANITIZE_THREAD__ */
       ssize_t sent = write(d_fd.getHandle(), &ptr, sizeof(ptr));
 
       if (sent == sizeof(ptr)) {
@@ -218,6 +235,9 @@ namespace channel
         return true;
       }
       else {
+#if __SANITIZE_THREAD__
+      __tsan_acquire(ptr);
+#endif /* __SANITIZE_THREAD__ */
         if (errno == EINTR) {
           continue;
         }
@@ -251,6 +271,9 @@ namespace channel
       T* obj{nullptr};
       ssize_t got = read(d_fd.getHandle(), &obj, sizeof(obj));
       if (got == sizeof(obj)) {
+#if __SANITIZE_THREAD__
+        __tsan_acquire(obj);
+#endif /* __SANITIZE_THREAD__ */
         return std::unique_ptr<T, D>(obj, deleter);
       }
       else if (got == 0) {
-- 
2.47.2