[Mesa-dev] [Bug 101556] [llvmpipe] crashes when GL context is created and a previous context was shared

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=101556

            Bug ID: 101556
           Summary: [llvmpipe] crashes when GL context is created and a
                    previous context was shared
           Product: Mesa
           Version: 17.1
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Mesa core
          Assignee: mesa-dev at lists.freedesktop.org
          Reporter: florianlink at gmail.com
        QA Contact: mesa-dev at lists.freedesktop.org

Created attachment 132131
  --> https://bugs.freedesktop.org/attachment.cgi?id=132131&action=edit
Screenshot of the crash, fence pointer is NULL.

I built the current 17.1.3 release on Windows Visual Studio 2015 with LLVM 3.9
(and 4.0 as well).

When I start my Qt application, which creates some GL contexts, I get the crash
that you can see in the attached images, when one of the contexts is created.

I tracked the crash down to the following commit (4 month ago):

https://github.com/mesa3d/mesa/commit/043883647acaee0b2c67c1c6b496404ebb4e8d67

As you can see in my screenshot, the fence pointer is NULL and it is not
checked before calling a function that needs a valid fence pointer.

It seems to happen when wglMakeCurrent(NULL,NULL) is called by Qt and the
context that was active before is a shared context, so the bad fence call
happens.

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