Re: Bug in "revision.c: --all adds HEAD from all worktrees" ?

From: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Date: Mar 12, 2018, 21:39 UTC
Message-ID: <878taxq8gm.fsf@evledraar.gmail.com>
In-Reply-To: <CAE5ih79wG3ws=OyXqvbd+QKyyAmM-D2JVO5r9G5VHtoOfiXdug@mail.gmail.com>

On Thu, Nov 16 2017, Luke Diamand jotted:

Show 66 quoted lines

> On 15 November 2017 at 22:08, Junio C Hamano <gitster@pobox.com> wrote:
>> Luke Diamand <luke@diamand.org> writes:
>>
>>> Quite a few of the worktrees have expired - their head revision has
>>> been GC'd and no longer points to anything sensible
>>> (gc.worktreePruneExpire). The function other_head_refs() in worktree.c
>>> bails out if there's an error, which I think is the problem. I wonder
>>> if it should instead just report something and then keep going.
>>
>> Am I correct to understand that your "git fsck" would fail because
>> these HEAD refs used by other stale worktrees are pointing at
>> missing objects?
>
> git fsck says:
>
> Checking object directories: 100% (256/256), done.
> Checking objects: 100% (1434634/1434634), done.
> error: HEAD: invalid reflog entry
> 7fa2b7ee4bc0d11529f659db8b13ed1f537d2a98
> error: HEAD: invalid reflog entry
> 7fa2b7ee4bc0d11529f659db8b13ed1f537d2a98
> error: HEAD: invalid reflog entry
> 7e79e09e8a7382f91610f7255a1b99ea59f68c0b
> error: refs/stash: invalid reflog entry
> feeb35e7b045d28943c706e761d0a2ac8206af2f
> error: refs/remotes/origin/master: invalid reflog entry
> 7fa2b7ee4bc0d11529f659db8b13ed1f537d2a98
> Checking connectivity: 1419477, done.
> missing tree 1480c0a7ed2ad59ae701667292399c38d294658e
> missing tree ca2a01116bfbbd1fcbcf9812b95d8dc6c39e69d5
> missing tree 5b7c41e547fc5c4c840e5b496da13d3daebc5fbe
> ...
> ...
>
>>
>> What do you mean by "expired"?  "Even though I want to keep using
>> them, Git for some reason decided to destroy them." or "I no longer
>> use them but kept them lying around."?
>
> git worktree automatically prunes work trees:
>
> "The working tree’s administrative files in the repository (see
> "DETAILS" below) will eventually be removed automatically (see
> gc.worktreePruneExpire in git-config(1)),"
>
> In my case I didn't actually want them removed, but fortunately
> there's nothing important in them (there certainly isn't anymore...).
>
>>
>> If the latter, I wonder "worktree prune" to remove the
>> admininstrative information for them would unblock you?
>
> It doesn't seem to help.
>
> $ git worktree prune -n
> <lists lots of unhappy trees>
> $ git worktree prune
> $ git fetch
> remote: Counting objects: 35, done.
> remote: Compressing objects: 100% (20/20), done.
> remote: Total 21 (delta 17), reused 5 (delta 1)
> Unpacking objects: 100% (21/21), done.
> fatal: bad object HEAD
> error: ssh://whatever/myrepol did not send all necessary objects
> $ /usr/bin/git-2.7.3 fetch
> <works fine>

Digging up this old thread. I've also noticed this bug because I tried to "git repack -A -d" a repo on a GitLab server and just got "fatal: bad object HEAD".

Bisect revealed that the reason was that GitLab itself runs 2.14.3, which is the last release version that doesn't have Duy's d0c39a49cc ("revision.c: --all adds HEAD from all worktrees", 2017-08-23), and that the HEAD revision of some worktrees was corrupt (GitLab creates squash-* worktrees for some reason).

Doing a "git worktree prune" beforehand makes it work.

This can be reproduced with:

    (
        rm -rf /tmp/git &&
        git clone --bare https://github.com/git/git.git /tmp/git &&
        cd /tmp/git &&
        git worktree add blah HEAD &&
        echo 1111111111111111111111111111111111111111 > worktrees/blah/HEAD
    )

Now, obviously the root cause is that the repo is corrupt through some other bug (since fixed?), but the error message here is really bad, and should at least say "fatal: bad object HEAD in worktree blah" or something like that.