Bug 102148

i've compiled the latest mesa version with llvmpipe on win32 (with
msvc2015) with
"scons build=debug MSVC_VERSION=14.0 opengl32" (with LLVM 4.0). The version i've compiled is 165be830fd822b8a76ee35080c214e2243d6d0f6 (from 07.08.2017 14:14:38).

Then I downloaded the QtCreator and tried to run the qopenglwidget example
(see
http://code.qt.io/cgit/qt/qtbase.git/tree/examples/opengl/qopenglwidget?h=5.6)
from Qt version 5.6. I copied the mesa opengl32.dll into the application
directory, but it immediately crashes on application startup.

This is the callstack i get in QtCreator:
1   RtlEnterCriticalSection                          ntdll
       0x779d22e2
2   mtx_lock                                         threads_win32.h
  436  0x3435cba
3   lp_fence_wait                                    lp_fence.c
 119  0x3436404
4   llvmpipe_fence_finish                            lp_screen.c
  616  0x3433ff9
5   st_context_flush                                 st_manager.c
 638  0x3040a08
6   stw_make_current                                 stw_context.c
  431  0x301d3cc
7   DrvSetContext                                    stw_context.c
  930  0x301cc3c
8   wglMakeCurrent                                   stw_wgl.c
  114  0x4e85eb3
9   QWindowsGLContext::updateObtainedParams          qwindowsglcontext.cpp
  1262 0xd09e6e
10  QWindowsGLContext::QWindowsGLContext             qwindowsglcontext.cpp
  1194 0xd09070
11  QOpenGLStaticContext::createContext              qwindowsglcontext.cpp
  266  0xd08a56
12  QWindowsIntegration::createPlatformOpenGLContext
qwindowsintegration.cpp 413  0xcae22e
13  QOpenGLContext::create                           qopenglcontext.cpp
 606  0xfab662e
14  QOpenGLWidgetPrivate::initialize                 qopenglwidget.cpp
  759  0x64da5bca
15  QOpenGLWidget::resizeEvent                       qopenglwidget.cpp
  1172 0x64da4ccd
16  QWidget::event                                   qwidget.cpp
  8913 0x64d68a1b
17  QOpenGLWidget::event                             qopenglwidget.cpp
  1345 0x64da4e99
18  QApplicationPrivate::notify_helper               qapplication.cpp
 3804 0x64d19b4b
19  QApplication::notify                             qapplication.cpp
 3767 0x64d17c7e
20  QCoreApplication::notifyInternal2                qcoreapplication.cpp
 1015 0x6641ee1c
... <More>


It crashes because the ctx passed into llvmpipe_fence_finish() is NULL.

Is this a known issue or is there some build option which might result in
some missing functionality which result in this kind of crash.