git clone fails intermittently if source repo is updated

Running "git clone master.git copy" sometimes fails if changes are being pushed to master.git. Likewise, running "git clone mirror.git copy" sometimes fails if the mirror is currently fetching changes from master.git.

In git 1.7.9 I sometimes get one of two fatal error messages. In one of the cases, git still exits with exit code 0, but the working directory of "copy" is not updated with the proper files. (See below for the exact error messages.)

In git 1.7.10 the mirror sometimes ends up in "detached HEAD" state. Sometimes it prints a warning message. (See below for the messages.)

The following shell scripts can reproduce the problem. I've been using a 4-core CPU on Ubuntu 11.04. I've compiled Git from source.

The first script, test-git-setup.sh, creates the directory "test-git" and three git repositories in it: master.git, mirror.git, and committer:

------ cut here for test-git-setup.sh ------
#!/bin/sh
mkdir test-git || exit 1
cd test-git
mkdir master.git
(cd master.git && git init --bare)
git clone master.git committer
(cd committer &&

    touch foo &&
    git add foo &&
    git commit -m"Initial commit" &&
    git push origin master)

git clone --mirror master.git mirror.git
------ cut here ------

The second script continuously modifies the file "foo" in the committer repository, commits it, and pushes it to master.git:

------ cut here for test-git-commit.sh ------
#!/bin/sh
set -e
cd test-git/committer
i=0
while :
do
echo $i > foo
git add foo
git commit -m"Updated foo"
git push
i=expr $i + 1
done
------ cut here ------

The third script repeatedly clones a repository, and ensures that the "git clone" command does exit 0, prints no unexpected output, and creates a sane clone (the file "foo" must exist). You must give it the argument "master" or "mirror" to tell it which repository to clone.

------ cut here for test-git-reclone.sh ------
#!/bin/sh

what=$1

case "$what" in

    master);;
    mirror);;
    *) echo need to specify master or mirror >&2
       exit 1;;

esac

good=0
cd test-git || exit 1
rm -rf $what-clone
while :
do

    git clone $what.git $what-clone >$what.out 2>$what.err || exit 1
    if [ -s $what.err ]
    then
	echo unexpected stderr from git clone:
	cat $what.err
	exit 1
    fi
    if [ "`cat $what.out`" != "Cloning into '$what-clone'...

done." ]
then
echo unexpected stdout from git clone:
cat $what.out
exit 1
fi
if ! [ -f $what-clone/foo ]
then
echo failed to create $what-clone/foo
exit 1
fi
rm -rf $what-clone
good=expr $good + 1
echo "$good good clones"
done
------ cut here ------

The final script repeatedly runs "git fetch" in mirror.git, to update it from master.git.

------ cut here for test-git-mirror.sh ------
#!/bin/sh
cd test-git/mirror.git
while :
do
echo running fetch...
git fetch || exit 1
echo done.
done
------ cut here ------

To reproduce, run this command:

    ./test-git-setup.sh

When it has completed, run the following commands at once (preferably in four separate windows so you can see what is going on). Start them in the indicated order.

./test-git-reclone.sh master
./test-git-reclone.sh mirror
./test-git-mirror.sh
./test-git-commit.sh

The reclone commands will print lines such as these:

1 good clones
2 good clones
3 good clones
4 good clones

Let them run to at least 200 good clones before you decide that you cannot reproduce the problem.

Using Git 1.7.10 I get the following error after a while:

When this happens, I can recover by running "git checkout master" in the clone, but before I do so "git status" reports:

and "git branch -a" reports:

Sometimes I get a different error:

or

Using Git 1.7.9 I sometimes get this error when running "./test-git-reclone.sh mirror":

Sometimes I get this message:

In this case, "git clone" does exit(0), but the file "foo" does not exist in the created mirror.

/ceder

For your convenience, I have now set up a Git repository where you can get slightly updated versions of the above scripts. The Gitorious web page is here:

http://git.lysator.liu.se/ceder/git-clone-fail-demo

You can clone it like this:

git clone git://git.lysator.liu.se/ceder/git-clone-fail-demo.git

I have been able to reproduce the problem on Git 1.6.0 as well, so this is apparently not a recent regression.

The problem can also be reproduces when you clone, push and fetch via ssh, but it happens a lot less frequently then. See the README file in the git-clone-fail-demo repository for info on how to reproduce it.

/ceder