From 332563cc1ef269a2550bf92629f5cd15ff1ae8f8 Mon Sep 17 00:00:00 2001
From: Alexey Milovidov <milovidov@clickhouse.com>
Date: Fri, 10 Apr 2026 04:06:34 +0000
Subject: [PATCH] Fix data race on `pmull_runtime_flag` in crc32c

The global `bool pmull_runtime_flag` is written from `IsFastCrc32Supported`
and `Choose_Extend` without synchronization, causing a TSan report when
multiple RocksDB instances are opened concurrently. Make it
`std::atomic<bool>` with relaxed ordering, since it is always set to the
same value.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
(cherry picked from commit dabb7ba1e714369d2a7d3f1a7482b98324f60554)
---
 util/crc32c.cc       | 7 ++++---
 util/crc32c_arm64.cc | 6 ++++--
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/util/crc32c.cc b/util/crc32c.cc
index c00276d765ce..107509271144 100644
--- a/util/crc32c.cc
+++ b/util/crc32c.cc
@@ -12,6 +12,7 @@
 #include "util/crc32c.h"
 
 #include <array>
+#include <atomic>
 #include <cstdint>
 #include <utility>
 
@@ -53,7 +54,7 @@ ASSERT_FEATURE_COMPAT_HEADER();
 #endif
 
 #if defined(HAVE_ARM64_CRC)
-bool pmull_runtime_flag = false;
+std::atomic<bool> pmull_runtime_flag{false};
 #endif
 
 namespace ROCKSDB_NAMESPACE::crc32c {
@@ -377,7 +378,7 @@ std::string IsFastCrc32Supported() {
   if (crc32c_runtime_check()) {
     has_fast_crc = true;
     arch = "Arm64";
-    pmull_runtime_flag = crc32c_pmull_runtime_check();
+    pmull_runtime_flag.store(crc32c_pmull_runtime_check(), std::memory_order_relaxed);
   } else {
     has_fast_crc = false;
     arch = "Arm64";
@@ -1108,7 +1109,7 @@ static inline Function Choose_Extend() {
   return isAltiVec() ? ExtendPPCImpl : ExtendImpl<DefaultCRC32>;
 #elif defined(HAVE_ARM64_CRC)
   if(crc32c_runtime_check()) {
-    pmull_runtime_flag = crc32c_pmull_runtime_check();
+    pmull_runtime_flag.store(crc32c_pmull_runtime_check(), std::memory_order_relaxed);
     return ExtendARMImpl;
   } else {
     return ExtendImpl<DefaultCRC32>;
diff --git a/util/crc32c_arm64.cc b/util/crc32c_arm64.cc
index 47c22c030fc5..2e90eb7a6cab 100644
--- a/util/crc32c_arm64.cc
+++ b/util/crc32c_arm64.cc
@@ -5,6 +5,8 @@
 
 #include "util/crc32c_arm64.h"
 
+#include <atomic>
+
 #if defined(HAVE_ARM64_CRC)
 
 #if defined(__linux__)
@@ -49,7 +51,7 @@
   } while (0)
 #endif
 
-extern bool pmull_runtime_flag;
+extern std::atomic<bool> pmull_runtime_flag;
 
 uint32_t crc32c_runtime_check(void) {
 #if defined(ROCKSDB_AUXV_GETAUXVAL_PRESENT) || defined(__FreeBSD__)
@@ -124,7 +126,7 @@ uint32_t crc32c_arm64(uint32_t crc, unsigned char const* data, size_t len) {
    * Raspberry Pi supports crc32 but doesn't support pmull.
    * Skip Crc32c Parallel computation if no crypto extension available.
    */
-  if (pmull_runtime_flag) {
+  if (pmull_runtime_flag.load(std::memory_order_relaxed)) {
 /* Macro (HAVE_ARM64_CRYPTO) is used for compiling check  */
 #ifdef HAVE_ARM64_CRYPTO
 /* Crc32c Parallel computation