From 0a5045a31ff9858846d5b7679f14ed45c47446b3 Mon Sep 17 00:00:00 2001
From: Sona Kurazyan <sona.kurazyan@qt.io>
Date: Mon, 18 Jul 2022 14:46:24 +0200
Subject: [PATCH] QtConcurrent::ReduceKernel: fix race conditions

resultsMapSize is modified inside the runReduce() method, and the
writes are protected via mutex lock. However, reads of resultsMapSize
through shouldThrottle()/shouldStartThread() (that can be called by
multiple threads) are done without a lock. Added the missing locks.

Task-number: QTBUG-104787
Change-Id: I700e7b66e67025bc7f570bc8ad69409b82675049
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
(cherry picked from commit 7afb093dd77f0ed9a1b4145d2d279810aba411c7)
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>
---
 src/concurrent/qtconcurrentreducekernel.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/concurrent/qtconcurrentreducekernel.h b/src/concurrent/qtconcurrentreducekernel.h
index a58739fc410..a2c693d9e2e 100644
--- a/src/concurrent/qtconcurrentreducekernel.h
+++ b/src/concurrent/qtconcurrentreducekernel.h
@@ -187,11 +187,13 @@ public:
 
     inline bool shouldThrottle()
     {
+        std::lock_guard<QMutex> locker(mutex);
         return (resultsMapSize > (ReduceQueueThrottleLimit * threadCount));
     }
 
     inline bool shouldStartThread()
     {
+        std::lock_guard<QMutex> locker(mutex);
         return (resultsMapSize <= (ReduceQueueStartLimit * threadCount));
     }
 };