Merge "fix race in ProcessState::getThreadPoolMaxTotalThreadCount" into main

1 files changed, 10 insertions, 2 deletions

diff --git a/libs/binder/ProcessState.cpp b/libs/binder/ProcessState.cpp
index a42ede29a2..7c29dba2d0 100644
--- a/libs/binder/ProcessState.cpp
+++ b/libs/binder/ProcessState.cpp
@@ -429,8 +429,17 @@ status_t ProcessState::setThreadPoolMaxThreadCount(size_t maxThreads) {
 }
 
 size_t ProcessState::getThreadPoolMaxTotalThreadCount() const {
+    // Need to read `mKernelStartedThreads` before `mThreadPoolStarted` (with
+    // non-relaxed memory ordering) to avoid a race like the following:
+    //
+    // thread A: if (mThreadPoolStarted) { // evaluates false
+    // thread B: mThreadPoolStarted = true;
+    // thread B: mKernelStartedThreads++;
+    // thread A: size_t kernelStarted = mKernelStartedThreads;
+    // thread A: LOG_ALWAYS_FATAL_IF(kernelStarted != 0, ...);
+    size_t kernelStarted = mKernelStartedThreads;
+
     if (mThreadPoolStarted) {
-        size_t kernelStarted = mKernelStartedThreads;
         size_t max = mMaxThreads;
         size_t current = mCurrentThreads;
 
@@ -460,7 +469,6 @@ size_t ProcessState::getThreadPoolMaxTotalThreadCount() const {
 
     // must not be initialized or maybe has poll thread setup, we
     // currently don't track this in libbinder
-    size_t kernelStarted = mKernelStartedThreads;
     LOG_ALWAYS_FATAL_IF(kernelStarted != 0, "Expecting 0 kernel started threads but have %zu",
                         kernelStarted);
     return mCurrentThreads;