Deadlock in QImage conversion, convert_generic_inplace hangs on futex

#0 0x00007f47572b013d in syscall () from target:/lib64/libc.so.6 
#1 0x00007f475952e8bc in bool futexSemaphoreTryAcquire<false>(QBasicAtomicInteger<unsigned long long>&, int, int) () from target:/tandberg/system/releases/hostos/x86_64/20210120-df1db18b3e9/lib/libQt5Core.so.5
#2 0x00007f4759dc504f in convert_generic_inplace(QImageData*, QImage::Format, QFlags<Qt::ImageConversionFlag>) () from target:/tandberg/system/releases/hostos/x86_64/20210120-df1db18b3e9/lib/libQt5Gui.so.5 
#3 0x000055cb315c040c in (anonymous namespace)::PhoenixHelmetRenderTest::runRenderTest(char const*, QString) () 
#4 0x000055cb315c0ed1 in (anonymous namespace)::(anonymous namespace)::register_verify_rendering_of_borderpixmap::register_verify_rendering_of_borderpixmap()::{lambda()#1}::operator()() const [clone .constprop.0] () 
#5 0x000055cb32b4f24c in cxx_unit_test::TestResult::run_test_crashing_on_unhandled_exceptions(cxx_unit_test::TestCase&) () 
#6 0x000055cb32b4e94c in cxx_unit_test::TestResult::run_test(cxx_unit_test::TestCase&) () 
#7 0x000055cb32b4a350 in cxx_unit_test::TestRegistry::listen_and_run(cxx_unit_test::TestResult&, cxx_unit_test::SystemCalls&) () #8 0x000055cb311d9e6b in main ()
 

commit 332816779c42e8a3fed34e9295c09338bc9b4945 
Author: Allan Sandfeld Jensen <allan.jensen@qt.io> 
Date:   Fri Nov 22 13:02:31 2019 +0100 
 
    Multithread some QImage routines 
     
    Use QThreadPool to process QImage smooth-scaling, format conversions, 
    and colorspace transforms multithreaded. 
     
    Change-Id: Ic142b1fa899f56e7e5099d36ca713701a47b681b 
    Reviewed-by: Lars Knoll <lars.knoll@qt.io>