From 9211d04730da7495fd2584e6768b73c3f86aba00 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?M=C3=A5rten=20Nordheim?= <marten.nordheim@qt.io>
Date: Thu, 25 Mar 2021 13:58:00 +0100
Subject: [PATCH] QSemaphore: move suspect increment of waiter count

We might return false a few lines down, without decreasing the count.

Change-Id: I0a90c07f279860987e41539e9d5f3b5d2cb15207
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/thread/qsemaphore.cpp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/corelib/thread/qsemaphore.cpp b/src/corelib/thread/qsemaphore.cpp
index ee4cee52811..5111d80ac6b 100644
--- a/src/corelib/thread/qsemaphore.cpp
+++ b/src/corelib/thread/qsemaphore.cpp
@@ -246,13 +246,13 @@ template <bool IsTimed> bool futexSemaphoreTryAcquire(QBasicAtomicInteger<quintp
     // we need to wait
     quintptr oneWaiter = quintptr(Q_UINT64_C(1) << 32); // zero on 32-bit
     if (futexHasWaiterCount) {
-        // increase the waiter count
-        u.fetchAndAddRelaxed(oneWaiter);
-
         // We don't use the fetched value from above so futexWait() fails if
         // it changed after the testAndSetOrdered above.
         if ((quint64(curValue) >> 32) == 0x7fffffff)
             return false;       // overflow!
+
+        // increase the waiter count
+        u.fetchAndAddRelaxed(oneWaiter);
         curValue += oneWaiter;
 
         // Also adjust nn to subtract oneWaiter when we succeed in acquiring.