linux-kernel - Re: data loss when doing ls-remote and piped to command

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Date:   Thu, 16 Sep 2021 17:49:59 +0200
From:   Mike Galbraith <efault@....de>
To:     Rolf Eike Beer <eb@...ix.com>, git@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Tobias Ulmer <tu@...ix.com>, Junio C Hamano <gitster@...ox.com>,
        linux-kernel@...r.kernel.org
Subject: Re: data loss when doing ls-remote and piped to command

On Thu, 2021-09-16 at 14:17 +0200, Rolf Eike Beer wrote:
> Am Donnerstag, 16. September 2021, 12:12:48 CEST schrieb Tobias Ulmer:
> > On 16/09/2021 08:38, Rolf Eike Beer wrote:
> > ...
> >
> > > The redirection seems to be an important part of it. I now did:
> > >
> > > git ... 2>&1 | sha256sum
> >
> > I've tried to reproduce this since yesterday, but couldn't until now:
> >
> > 2>&1 made all the difference, took less than a minute.
> >
> > Different repo, different machine, but also running Tumbleweed
> > 5.14.1-1-default, git 2.33.0
> >
> > while [ "`git --git-dir=$PWD/in/linux/.git ls-remote origin 2>&1 | tee
> > failed.out | sha1sum`" = "7fa299e589bacdc908395730beff542b0fc684eb  -"
> > ]; do echo -n .; done
> > ..........
> >
> > failed.out has multiple lines like this:
> >
> > --8<--
> > 4e77f7f1261f65cff06918bc5e66d02a418fc842        refs/tags/v3.10.18^{}
> > f7b8df0cc81cf82a4ac6834225bddbe46a340455a4a5d52f29d08d923ce8d232b0b497da674d
> > d2c refs/tags/v3.18
> > b2776bf7149bddd1f4161f14f79520f17fc1d71d        refs/tags/v3.18^{}
> > --8<--
> >
> >
> > Running the same on Archlinux (5.13.13-arch1-1, 2.33.0) doesn't show the
> > problem.
> > This may well turn out not to be git, but a kernel issue.
>
> Linus,
>
> since you have been hacking around in pipe.c recently, I fear this isn't
> entirely impossible. Have you any idea?
>
> For easier reference, the complete thread is at:
>
> https://public-inbox.org/git/85a103f6-8b3c-2f21-cc0f-04f517c0c9a1@emlix.com/T/
>

I use git-daemon (2.33) and reference clones for my local pile of
kernel trees (74), so out of curiosity, modified the above ls-remote
loop to fit one of them, and tried to reproduce with both master.today
(ff1ffd71) and SUSE's stable branch (where Tumbleweed gets source,
currently at 5.14.4).  Both kernels failed to reproduce given a few
minutes each (zzzz) to do so.  I'm running Leap-15.3 vs Tumbleweed, but
that shouldn't matter.

	-Mike