[PATCH 0/6] deadlock regression in v2.11.0 with failed mkdtemp

From: Jeff King <peff@peff.net>
Date: Mar 7, 2017, 13:34 UTC
Message-ID: <20170307133437.qee2jtynbiwf6uzr@sigill.intra.peff.net>
In-Reply-To: <20170307111406.GB1955@quickstop.soohrt.org>

On Tue, Mar 07, 2017 at 12:14:06PM +0100, Horst Schirmeier wrote:

Show 15 quoted lines

> On Tue, 07 Mar 2017, Horst Schirmeier wrote:
> > I observe a regression that seems to have been introduced between
> > v2.10.0 and v2.11.0.  When I try to push into a repository on the local
> > filesystem that belongs to another user and has not explicitly been
> > prepared for shared use, v2.11.0 shows some of the usual diagnostic
> > output and then freezes instead of announcing why it failed to push.
> 
> Bisecting points to v2.10.1-373-g722ff7f:
> 
> 722ff7f876c8a2ad99c42434f58af098e61b96e8 is the first bad commit
> commit 722ff7f876c8a2ad99c42434f58af098e61b96e8
> Author: Jeff King <peff@peff.net>
> Date:   Mon Oct 3 16:49:14 2016 -0400
> 
>     receive-pack: quarantine objects until pre-receive accepts

Thanks, I was able to reproduce easily with:

  git init --bare foo.git
  chown -R nobody foo.git
  git push foo.git HEAD

Here's a series to fix it. The first patch addresses the deadlock. The rest try to improve the output on the client side. With v2.10.0, this case looks like:

  $ git push ~/tmp/foo.git HEAD
  Counting objects: 209837, done.
  Delta compression using up to 8 threads.
  Compressing objects: 100% (52180/52180), done.
  remote: fatal: Unable to create temporary file '/home/peff/tmp/foo.git/./objects/pack/tmp_pack_XXXXXX': Permission denied
  error: failed to push some refs to '/home/peff/tmp/foo.git'

With just the first patch applied, you get just:

  $ git push ~/tmp/foo.git HEAD
  Counting objects: 210973, done.
  Delta compression using up to 8 threads.
  Compressing objects: 100% (52799/52799), done.
  error: failed to push some refs to '/home/peff/tmp/foo.git'

Yuck. In the original, the error was generated by the child index-pack, and we relayed it over the sideband. But we don't even get as far as running index-pack in the newer version; we fail trying to make the tmpdir. The error ends up in the "unpack" protocol field, but the client side does a bad job of showing that. With the rest of the patches, it looks like:

  $ git push ~/tmp/foo.git HEAD
  Counting objects: 210973, done.
  Delta compression using up to 8 threads.
  Compressing objects: 100% (52799/52799), done.
  error: remote unpack failed: unable to create temporary object directory
  error: failed to push some refs to '/home/peff/tmp/foo.git'

Compared to v2.10.0, that omits the name of the directory and the errno value (because receive-pack does not send them). That potentially makes debugging harder, but arguably it's the right thing to do. On a remote site, those details aren't really the client's business. But if people feel strongly, we could add them back into this error code path.

So the first patch is a no-brainer and should go to maint. The rest can be applied separately if need be.

  [1/6]: receive-pack: fix deadlock when we cannot create tmpdir
  [2/6]: send-pack: extract parsing of "unpack" response
  [3/6]: send-pack: use skip_prefix for parsing unpack status
  [4/6]: send-pack: improve unpack-status error messages
  [5/6]: send-pack: read "unpack" status even on pack-objects failure
  [6/6]: send-pack: report signal death of pack-objects

 builtin/receive-pack.c |  5 ++++-
 send-pack.c            | 46 ++++++++++++++++++++++++++++++++++++----------
 2 files changed, 40 insertions(+), 11 deletions(-)

-Peff