[Mesa-dev] [Bug 101252] eglGetDisplay() is not thread safe

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=101252

            Bug ID: 101252
           Summary: eglGetDisplay() is not thread safe
           Product: Mesa
           Version: git
          Hardware: Other
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: EGL
          Assignee: mesa-dev at lists.freedesktop.org
          Reporter: eucan at de.adit-jv.com
        QA Contact: mesa-dev at lists.freedesktop.org

Created attachment 131599
  --> https://bugs.freedesktop.org/attachment.cgi?id=131599&action=edit
Sample code for reproducing the bug

Hello,

We found out this issue in our GPU driver tests. It happens when many threads
are created and every thread creates wl_display object and calls
eglGetDisplay(). Then, some threads are getting EGL_NO_DISPLAY.

I implemented a sample code for reproducing the bug (main.c). The issue occurs
very often when I run the binary with 300 threads. I tried it in mesa 11.2 but
I saw the related code for upstream is the same.

I debugged mesa code and I found out that a thread gets EGL_NO_DISPLAY only
when _eglGetNativePlatform() returns _EGL_INVALID_PLATFORM.

native_platform variable is defined as static in _eglGetNativePlatform().
Therefore, different threads are sharing the same variable. When I remove the
static keyword and recompile mesa binaries, the issue never occurs.

In my platform, EGL_PLATFORM and EGL_DISPLAY env variables are never defined.
Therefore, _eglGetNativePlatformFromEnv() function always returns
_EGL_INVALID_PLATFORM.

I think issue occurs when a thread is in the end of _eglGetNativePlatform()
just before returning found native_platform, and the other thread overwrites
this static variable in _eglNativePlatformFromEnv() function.

Most likely issue is introduced by this commit:
7adb9b094894a512c019b3378eb9e3c69d830edc

Best Regards,
Emre Ucan

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