Re: git name-rev segfault

[Jeff King <peff@peff.net>]

On Mon, Jul 29, 2019 at 04:19:47PM +0200, Tamas Papp wrote:

> Generate 100k file into a repository:
> 
> #!/bin/bash
> 
> rm -rf .git test.file
> git init
> git config user.email a@b
> git config user.name c
> 
> time for i in {1..100000}
> do
>   [ $((i % 2)) -eq 1 ] && echo $i>test.file || echo 0 >test.file
>   git add test.file
> 
>   git commit -m "$i committed"
> 
> done

I lost patience kicking off two hundred thousand processes. Try this:

  for i in {1..100000}
  do
    echo "commit HEAD"
    echo "committer c <a@b> $i +0000"
    echo "data <<EOF"
    echo "$i committed"
    echo "EOF"
    echo
  done | git fast-import

which runs much faster. This doesn't change any files in each commit,
but I don't think it's necessary for what you're showing (name-rev
wouldn't ever look at the trees).

> Run git on it:
> 
> $ git name-rev a20f6989b75fa63ec6259a988e38714e1f5328a0

Anybody who runs your script will get a different sha1 because of the
change in timestamps. I guess this is HEAD, though. I also needed to
have an actual tag to find. So:

  git tag old-tag HEAD~99999
  git name-rev HEAD

segfaults for me.

> Could you coment on it?

This is a known issue. The algorithm used by name-rev is recursive, and
you can run out of stack space in some deep cases. There's more
discussion this thread:

  https://public-inbox.org/git/6a4cbbee-ffc6-739b-d649-079ba01439ca@grubix.eu/

including some patches that document the problem with an expected
failure in our test suite. Nobody has actually rewritten the C code yet,
though.

-Peff