Bare repository fetch/push race condition

Bare repository fetch/push race condition

[Dmitry Neverov]

It looks like there is a race condition between fetch and push in a
bare repository in the following setup. There is a bare git repository
on a local file system. Some process pushes to this repository via
jgit. There is a cron task which pushes this repository to the backup
remote repo over ssh. We observe the following in the reflog:

6932a831843f4dbe3b394acde9adc9a8269b6cf1
57b77b8c2a04029e7f5af4d3b7e36a3ba0c7cac9 XXX 1505903078 +0200    push:
forced-update
57b77b8c2a04029e7f5af4d3b7e36a3ba0c7cac9
44a221b0271b9abc885dd6e54f691d5248c4171f XXX 1505905206 +0200    push:
forced-update
44a221b0271b9abc885dd6e54f691d5248c4171f
57b77b8c2a04029e7f5af4d3b7e36a3ba0c7cac9 YYY    1505905217 +0200
update by push

Where XXX is the process pushing via jgit and YYY is the cron task. It
looks like the cron task started a push when the ref was pointing to
57b77b8c2a04029e7f5af4d3b7e36a3ba0c7cac9 and push finished when the
ref was already updated to 44a221b0271b9abc885dd6e54f691d5248c4171f.
The push unconditionally updated the local tracking branch back to the
commit 57b77b8c2a04029e7f5af4d3b7e36a3ba0c7cac9 and we lost the commit
44a221b0271b9abc885dd6e54f691d5248c4171f since the next push from the
local process created a new commit with
57b77b8c2a04029e7f5af4d3b7e36a3ba0c7cac9 as a parent.

Shouldn't the update_ref at transport.c:308 specify the expected
old hash, like this:

    update_ref("update by push", rs.dst, ref->new_oid.hash,
ref->old_oid.hash, 0, 0);

at least for bare repositories?

Re: Bare repository fetch/push race condition

[Dmitry Neverov]

Sorry for misleading subject. It should be "Race condition between pushing to and pushing from a bare repository"