[Mesa-dev] [PATCH] r600g-llvm: Crude fix for a race in initialization of the llvm backend

[Tom Stellard]

On Thu, Aug 16, 2012 at 02:39:48PM -0400, Tom Stellard wrote:
> On Thu, Aug 16, 2012 at 07:44:53PM +0200, Mathias Fröhlich wrote:
> > 
> > Hi,
> > 
> > > This is likely caused by the fact that the same LLVM Context is used
> > > for all threads.  Take a look at the comment starting at
> > > src/gallium/auxilary/gallivm/lp_bld_init.c:314
> > >
> > > You should be able to reproduce this error on llvmpipe as well.
> > > Creating a new LLVM Context for each thread should fix this.
> > 
> > I checked the suggestion, but: Are you sure?
> > I think we are using a new context for r* even per compile.
> > See radeon_setup_tgsi_llvm.c:1009.
> >
> 
> You're right.  I missed that.
> 
> > I have spent some time now to look into this a little closer:
> > The observation is that some pass manager stuff is crashing usually.
> > Its from the addPassesToEmitFile call while setting up 
> > AMDGPUTargetMachine but if you lock just this it crashes mostly in 
> > LLVMAddPromoteMemoryToRegisterPass called from radeon_llvm_finalize_module.
> > Locking both with the same mutex appears to work for a few short tests.
> >
> > Does this ring an other bell at the llvm guys?
> > 
> 

Actually, I just noticed that the LLVM docs say that only one thread can
access the target registry at a time:
http://llvm.org/docs/doxygen/html/structllvm_1_1TargetRegistry.html#a0b078b468553a84ec2b9fd70e93f7b43

Also, I think we should be doing the target registry once per
context rather than once per compile.

-Tom

> I'm not really sure about this one.  It might be worth while to see if
> you can reproduce the bug with the r600 backend built with LLVM rather
> than Mesa.  I have LLVM and Mesa branches that make this possible:
> 
> LLVM: http://cgit.freedesktop.org/~tstellar/llvm/ r600-master
> Mesa: cgit.freedesktop.org/~tstellar/mesa/ r600-external-llvm
> 
> I haven't tested it in a while, though, so it may not work.
> 
> -Tom
> 
> 
> 
> > Greetings
> > 
> > Mathias
> > 
> > 
> > _______________________________________________
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> > mesa-dev at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/mesa-dev
> > 
> 
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