[Mesa-dev] [Bug 100627] EGL fails to fall back to DRI2 when DRI3 is enabled but not available

Sun Apr 9 11:55:02 UTC 2017

https://bugs.freedesktop.org/show_bug.cgi?id=100627

            Bug ID: 100627
           Summary: EGL fails to fall back to DRI2 when DRI3 is enabled
                    but not available
           Product: Mesa
           Version: 17.0
          Hardware: All
                OS: FreeBSD
            Status: NEW
          Severity: normal
          Priority: medium
         Component: EGL
          Assignee: mesa-dev at lists.freedesktop.org
          Reporter: rezny at FreeBSD.org
        QA Contact: mesa-dev at lists.freedesktop.org

DRI2 will be available but DRI3 may or may not depending which kernel and
drivers are running. When Mesa is compiled with DRI3 support enabled and run on
a kernel with only DRI2 support, applications using GLX work fine (modulo scary
messages), but applications that use EGL fail. The cause appears to be
insufficient checking during init in libEGL.

The GLX init code has separate dri3_create_screen and dri2_create_screen
functions which are called from the respective init function. When the former
bails with "libGL error: Version 7 or imageFromFds image extension not
found\nlibGL error: failed to load driver: r600", libGL then tries the DRI2
path and succeeds. As an aside, it would be nice if the first message was only
shown if LIBGL_DEBUG is set, and the second should indicate that DRI3 init has
failed but DRI2 will be attempted instead of saying the driver failed to load
(which is a source of spurious bug reports).

The EGL path on the other hand only has a dri2_create_screen function which is
called from both dri2_initialize_x11_dri2 and dri2_initialize_x11_dri3. Thus
the init path succeeds for DRI3 even though it cannot work, so the application
ultimately fails because the first detectable error is after we are out of the
init routines and it's too late to attempt a fallback to DRI2. Setting
LIBGL_DRI3_DISABLE allows applications using EGL to function correctly, so
there is a work-around until the initialization can be fixed to check
availability of DRI3 support as is done in libGL.

Example of failure running mesa EGL demos:

% LIBGL_DEBUG=verbose EGL_LOG_LEVEL=debug MESA_DEBUG=1 eglgears_x11             
libEGL debug: Native platform type: x11 (autodetected)
libEGL debug: added egl_dri2 to module array
libGL: Can't open configuration file /home/user/.drirc: No such file or
directory.
libEGL debug: DRI2: dlopen(/usr/local/lib/dri/r600_dri.so)
libEGL debug: found extension `DRI_Core'
libEGL info: found extension DRI_Core version 1
libEGL debug: found extension `DRI_IMAGE_DRIVER'
libEGL info: found extension DRI_IMAGE_DRIVER version 1
libEGL debug: found extension `DRI_DRI2'
libEGL debug: found extension `DRI_ConfigOptions'
libEGL debug: found extension `DRI2_Fence'
libGL: Can't open configuration file /home/user/.drirc: No such file or
directory.
libGL: Can't open configuration file /home/user/.drirc: No such file or
directory.
libEGL debug: found extension `DRI_TexBuffer'
libEGL info: found extension DRI_TexBuffer version 2
libEGL debug: found extension `DRI2_Flush'
libEGL info: found extension DRI2_Flush version 4
libEGL debug: found extension `DRI_IMAGE'
libEGL info: found extension DRI_IMAGE version 12
libEGL debug: found extension `DRI_RENDERER_QUERY'
libEGL debug: found extension `DRI_CONFIG_QUERY'
libEGL debug: found extension `DRI2_Throttle'
libEGL debug: found extension `DRI2_Fence'
libEGL debug: found extension `DRI2_Interop'
libEGL debug: found extension `DRI_TexBuffer'
libEGL debug: found extension `DRI2_Flush'
libEGL debug: found extension `DRI_IMAGE'
libEGL debug: found extension `DRI_RENDERER_QUERY'
libEGL info: found extension DRI_RENDERER_QUERY version 1
libEGL debug: found extension `DRI_CONFIG_QUERY'
libEGL info: found extension DRI_CONFIG_QUERY version 1
libEGL debug: found extension `DRI2_Throttle'
libEGL debug: found extension `DRI2_Fence'
libEGL info: found extension DRI2_Fence version 2
libEGL debug: found extension `DRI2_Interop'
libEGL info: found extension DRI2_Interop version 1
libEGL debug: did not find optional extension DRI_Robustness version 1
libEGL info: Using DRI3
libEGL debug: the best driver is DRI2
EGL_VERSION = 1.4 (DRI2)
zsh: segmentation fault (core dumped)

As can be seen, libEGL runs right through the DRI3 init and then crashes when
it tries to draw without having a surface. The backtrace differs according to
the driver in use. This is just an example from my machine:

(lldb) bt
* thread #1
  * frame #0: r600_dri.so`_debug_assert_fail(expr="surface",
file="state_tracker/st_atom_framebuffer.c", line=61,
function="update_framebuffer_size") at u_debug.c:321
    frame #1:
r600_dri.so`update_framebuffer_size(framebuffer=0x000000080a845028,
surface=0x0000000000000000) at st_atom_framebuffer.c:61
    frame #2: r600_dri.so`update_framebuffer_state(st=0x000000080a843000) at
st_atom_framebuffer.c:181
    frame #3: r600_dri.so`st_validate_state(st=0x000000080a843000,
pipeline=ST_PIPELINE_RENDER) at st_atom.c:219
    frame #4: r600_dri.so`st_Clear(ctx=0x000000080a85ff00, mask=18) at
st_cb_clear.c:409
    frame #5: r600_dri.so`_mesa_Clear(mask=16640) at clear.c:224
    frame #6: 0x0000000000401fde
eglgears_x11`___lldb_unnamed_symbol6$$eglgears_x11 + 14
    frame #7: 0x0000000000403a37
eglgears_x11`___lldb_unnamed_symbol30$$eglgears_x11 + 295
    frame #8: 0x0000000000401e97
eglgears_x11`___lldb_unnamed_symbol3$$eglgears_x11 + 423
    frame #9: 0x0000000000401bef
eglgears_x11`___lldb_unnamed_symbol1$$eglgears_x11 + 383

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