[PATCH] D31063: LTO: Fix a potential race condition in the caching API.

[Peter Collingbourne via Phabricator via llvm-commits]

pcc added a comment.

Is there a rename syscall immediately before the open syscall? If that is the case, the fatal error is probably coming from Caching.cpp:73, which is unexpected because we just put a file in place with the correct name, so maybe something is going on with the filesystem on that machine?

The other alternative is that the error is coming from Caching.cpp:41, and in that case the file not existing is expected. If the file does not exist we are supposed to fail the if condition on line 40 and create a new cache entry.

The only explanation I can think of is that there is some sort of bug in your stdlib that causes the if condition to succeed. What happens if you apply this patch?

  diff --git a/llvm/lib/LTO/Caching.cpp b/llvm/lib/LTO/Caching.cpp
  index d8b91c48ee3..c24540e1860 100644
  --- a/llvm/lib/LTO/Caching.cpp
  +++ b/llvm/lib/LTO/Caching.cpp
  @@ -37,7 +37,8 @@ Expected<NativeObjectCache> lto::localCache(StringRef CacheDirectoryPath,
         return AddStreamFn();
       }
   
  -    if (MBOrErr.getError() != std::errc::no_such_file_or_directory)
  +    if (MBOrErr.getError() != std::errc::no_such_file_or_directory &&
  +        MBOrErr.getError().message() != "No such file or directory")
         report_fatal_error(Twine("Failed to open cache file ") + EntryPath +
                            ": " + MBOrErr.getError().message() + "\n");
   


Repository:
  rL LLVM

https://reviews.llvm.org/D31063