Re: Don't clean up LLVM state when exiting in a bad way

Hi,

On 2021-08-18 15:00:59 +0000, Jelte Fennema wrote:
> I ran into some segfaults when using Postgres that was compiled with LLVM
> 7. According to the backtraces these crashes happened during the call to
> llvm_shutdown, during cleanup after another out of memory condition. It
> seems that calls to LLVMOrcDisposeInstance, can crash (at least on LLVM 7)
> when LLVM is left in bad state. I attached the relevant part of the
> stacktrace to this email.

> With the attached patch these segfaults went away. The patch turns
> llvm_shutdown into a no-op whenever the backend is exiting with an
> error. Based on my understanding of the code this should be totally fine. No
> memory should be leaked, since all memory will be cleaned up anyway once the
> backend exits shortly after. The only reason this cleanup code even seems to
> exist at all is to get useful LLVM profiling data. To me it seems be
> acceptable if the profiling data is incorrect/missing when the backend exits
> with an error.

I think this is a tad too strong. We should continue to clean up on exit as
long as the error didn't happen while we're already inside llvm
code. Otherwise we loose some ability to find leaks. How about checking in the
error path whether fatal_new_handler_depth is > 0, and skipping cleanup in
that case? Because that's precisely when it should be unsafe to reenter LLVM.

Greetings,

Andres Freund