[lld] r248102 - COFF: Fix thread-safety bug.

[Peter Collingbourne via llvm-commits]

LTOModule owns a Module under the covers, so any client that creates multiple
LTOModules in the same LLVMContext will be affected.

Maybe it's time for something like an LLVMContext-wide mutex, but that would
present its own design issues (e.g. we would need to define exactly where
guards should go) so I'd prefer to let clients worry about this until we
have a good sense of the right design.

Peter

On Sat, Sep 19, 2015 at 06:22:47PM -0700, Rui Ueyama via llvm-commits wrote:
> I have no idea. CC'ing Peter since he may know about that.
> 
> On Sat, Sep 19, 2015 at 5:31 PM, David Blaikie <dblaikie at gmail.com> wrote:
> 
> >
> >
> > On Sat, Sep 19, 2015 at 4:14 PM, Rui Ueyama via llvm-commits <
> > llvm-commits at lists.llvm.org> wrote:
> >
> >> Author: ruiu
> >> Date: Sat Sep 19 18:14:51 2015
> >> New Revision: 248102
> >>
> >> URL: http://llvm.org/viewvc/llvm-project?rev=248102&view=rev
> >> Log:
> >> COFF: Fix thread-safety bug.
> >>
> >> LTOModule doesn't seem to be thread-safe, so guard that with mutex.
> >>
> >
> > Yeah, that seems unfortunate.
> >
> > Any idea where the thread unsafety comes from & whether we can/should fix
> > it down the stack rather than in lld?
> >
> >
> >>
> >> Modified:
> >>     lld/trunk/COFF/InputFiles.cpp
> >>     lld/trunk/COFF/InputFiles.h
> >>
> >> Modified: lld/trunk/COFF/InputFiles.cpp
> >> URL:
> >> http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/InputFiles.cpp?rev=248102&r1=248101&r2=248102&view=diff
> >>
> >> ==============================================================================
> >> --- lld/trunk/COFF/InputFiles.cpp (original)
> >> +++ lld/trunk/COFF/InputFiles.cpp Sat Sep 19 18:14:51 2015
> >> @@ -310,6 +310,9 @@ void ImportFile::parse() {
> >>  }
> >>
> >>  void BitcodeFile::parse() {
> >> +  // Usually parse() is thread-safe, but bitcode file is an exception.
> >> +  std::lock_guard<std::mutex> Lock(Mu);
> >> +
> >>    std::string Err;
> >>    M.reset(LTOModule::createFromBuffer(MB.getBufferStart(),
> >>                                        MB.getBufferSize(),
> >> @@ -356,5 +359,7 @@ MachineTypes BitcodeFile::getMachineType
> >>    }
> >>  }
> >>
> >> +std::mutex BitcodeFile::Mu;
> >> +
> >>  } // namespace coff
> >>  } // namespace lld
> >>
> >> Modified: lld/trunk/COFF/InputFiles.h
> >> URL:
> >> http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/InputFiles.h?rev=248102&r1=248101&r2=248102&view=diff
> >>
> >> ==============================================================================
> >> --- lld/trunk/COFF/InputFiles.h (original)
> >> +++ lld/trunk/COFF/InputFiles.h Sat Sep 19 18:14:51 2015
> >> @@ -17,6 +17,7 @@
> >>  #include "llvm/Object/COFF.h"
> >>  #include "llvm/Support/StringSaver.h"
> >>  #include <memory>
> >> +#include <mutex>
> >>  #include <set>
> >>  #include <vector>
> >>
> >> @@ -213,6 +214,7 @@ private:
> >>    std::vector<SymbolBody *> SymbolBodies;
> >>    llvm::BumpPtrAllocator Alloc;
> >>    std::unique_ptr<LTOModule> M;
> >> +  static std::mutex Mu;
> >>  };
> >>
> >>  } // namespace coff
> >>
> >>
> >> _______________________________________________
> >> llvm-commits mailing list
> >> llvm-commits at lists.llvm.org
> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
> >>
> >
> >

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-- 
Peter