[Mesa-dev] [PATCH v4 (part2) 04/56] i965: set ARB_shader_storage_buffer_object related constant values

[Iago Toral]

On Thu, 2015-09-03 at 13:52 +0300, Tapani Pälli wrote:
> 
> On 09/03/2015 01:40 PM, Samuel Iglesias Gonsálvez wrote:
> >
> >
> > On 03/09/15 12:30, Tapani Pälli wrote:
> >> Hi;
> >>
> >> On 07/23/2015 09:42 AM, Samuel Iglesias Gonsalvez wrote:
> >>> v2:
> >>> - Add tessellation shader constants assignment
> >>>
> >>> Signed-off-by: Samuel Iglesias Gonsalvez <siglesias at igalia.com>
> >>> ---
> >>>    src/mesa/drivers/dri/i965/brw_context.c | 12 ++++++++++++
> >>>    1 file changed, 12 insertions(+)
> >>>
> >>> diff --git a/src/mesa/drivers/dri/i965/brw_context.c
> >>> b/src/mesa/drivers/dri/i965/brw_context.c
> >>> index b08a53b..a5c7b91 100644
> >>> --- a/src/mesa/drivers/dri/i965/brw_context.c
> >>> +++ b/src/mesa/drivers/dri/i965/brw_context.c
> >>> @@ -551,6 +551,18 @@ brw_initialize_context_constants(struct
> >>> brw_context *brw)
> >>>       ctx->Const.TextureBufferOffsetAlignment = 16;
> >>>       ctx->Const.MaxTextureBufferSize = 128 * 1024 * 1024;
> >>>
> >>> +   /* FIXME: Tessellation stages are not yet supported in i965, so
> >>> +    * MaxCombinedShaderStorageBlocks doesn't take them into account.
> >>> +    */
> >>> +   ctx->Const.Program[MESA_SHADER_VERTEX].MaxShaderStorageBlocks = 12;
> >>> +   ctx->Const.Program[MESA_SHADER_GEOMETRY].MaxShaderStorageBlocks = 12;
> >>> +   ctx->Const.Program[MESA_SHADER_TESS_EVAL].MaxShaderStorageBlocks = 0;
> >>> +   ctx->Const.Program[MESA_SHADER_TESS_CTRL].MaxShaderStorageBlocks = 0;
> >>> +   ctx->Const.Program[MESA_SHADER_FRAGMENT].MaxShaderStorageBlocks = 12;
> >>> +   ctx->Const.Program[MESA_SHADER_COMPUTE].MaxShaderStorageBlocks = 12;
> >>> +   ctx->Const.MaxCombinedShaderStorageBlocks = 12 * 3;
> >>> +   ctx->Const.MaxShaderStorageBufferBindings = 48;
> >>
> >> I think there is something funny with MaxShaderStorageBufferBindings
> >> value calculation. Commit 28ef0f83 adds 12 to it and then this commit
> >> overwrites it as 48. Without compute shaders I guess this value should
> >> be 48 - 12?
> >>
> >> I guess earlier '+12' should be removed and this part should be modified
> >> to calculate based on what is supported. For me '48 -12' fixes a few
> >> crashes I'm getting with
> >> "igalia/wip/siglesias/ARB_shader_storage_buffer_object-v4.3" branch I've
> >> used for some testing.
> >>
> >
> > I see. We are going to review the MaxShaderStorageBufferBindings
> > calculation, thanks for the report and the ideas.
> >
> > Can you share with us the tests that crashed because of this? You can
> > send them privately to me, if needed.
> 
> These are some Piglit tests that use buffer objects. Crash happens at 
> _mesa_free_buffer_objects(), it's not quite clear yet to me why (maybe 
> memory gets trashed) but I bisected it to this commit changing 
> MaxShaderStorageBufferBindings. For example 
> 'arb_framebuffer_no_attachments-atomic' segfaults when destroying the 
> context and calling _mesa_free_buffer_objects().
> 
> Here's example backtrace:
> (gdb) bt
> #0  0x00007ffff3dae830 in pthread_mutex_lock () from /lib64/libpthread.so.0
> #1  0x00007ffff1da8681 in mtx_lock (mtx=0xffffffffffffffff) at 
> ../../include/c11/threads_posix.h:192
> #2  _mesa_reference_buffer_object_ (ctx=0x7ffff7fd0040, 
> ptr=0x7ffff7ff13d0, bufObj=0x0) at main/bufferobj.c:450
> #3  0x00007ffff1da9173 in _mesa_reference_buffer_object (bufObj=0x0, 
> ptr=<optimized out>, ctx=0x7ffff7fd0040) at main/bufferobj.h:123
> #4  _mesa_free_buffer_objects (ctx=ctx at entry=0x7ffff7fd0040) at 
> main/bufferobj.c:907
> #5  0x00007ffff1db553b in _mesa_free_context_data 
> (ctx=ctx at entry=0x7ffff7fd0040) at main/context.c:1342
> #6  0x00007ffff2077a3e in intelDestroyContext (driContextPriv=0x6392f0) 
> at brw_context.c:996
> 
> it crashes because 'oldObj' in _mesa_reference_buffer_object_ points to 
> 0xffffffffffffffff.

Thanks for reporting this, the problem with the crash is that there is a
mismatch between the number of bindings used by the driver and the
maximum declared by Mesa, this was actually a silly mistake we
introduced after updating some of our code during reviews. To fix this
you need to set MAX_SHADER_STORAGE_BUFFERS in src/mesa/main/config.h to
15 (instead of the current value of 7, the issue comes from 7*6 = 42 <
48).

Samuel is going to look into the +12 issue you also mentioned.

Iago