From: "SZEDER Gábor" <szeder.dev@gmail.com>
To: Elijah Newren <newren@gmail.com>
Cc: Elijah Newren via GitGitGadget <gitgitgadget@gmail.com>,
Git Mailing List <git@vger.kernel.org>
Subject: Re: [PATCH 4/5] t6022, t6046: test expected behavior instead of testing a proxy for it
Date: Thu, 12 Mar 2020 21:01:57 +0100 [thread overview]
Message-ID: <20200312200157.GE3122@szeder.dev> (raw)
In-Reply-To: <CABPp-BGR_eDHJmNOPVQLx8WkL5WLV6J0NtQJ2=AE7CQB2sck5g@mail.gmail.com>
On Thu, Mar 12, 2020 at 10:35:52AM -0700, Elijah Newren wrote:
> On Thu, Mar 12, 2020 at 9:48 AM Elijah Newren <newren@gmail.com> wrote:
> >
> > On Thu, Mar 12, 2020 at 6:20 AM SZEDER Gábor <szeder.dev@gmail.com> wrote:
> > >
> > > On Thu, Feb 27, 2020 at 12:14:23AM +0000, Elijah Newren via GitGitGadget wrote:
> > > > From: Elijah Newren <newren@gmail.com>
> > > >
> > > > In t6022, we were testing for file being overwritten (or not) based on
> > > > an output message instead of checking for the file being overwritten.
> > > > Since we can check for the file being overwritten via mtime updates,
> > > > check that instead.
> > > >
> > > > In t6046, we were largely checking for both the expected behavior and a
> > > > proxy for it, which is unnecessary. The calls to test-tool also were a
> > > > bit cryptic. Make them a little clearer.
> > > >
> > > > Signed-off-by: Elijah Newren <newren@gmail.com>
> > > > ---
> > > > t/t6022-merge-rename.sh | 15 ++++-
> > > > t/t6046-merge-skip-unneeded-updates.sh | 89 +++++++++++++++++---------
> > > > 2 files changed, 70 insertions(+), 34 deletions(-)
> > > >
> > > > diff --git a/t/t6022-merge-rename.sh b/t/t6022-merge-rename.sh
> > > > index 6f196aaf276..d97cf48495b 100755
> > > > --- a/t/t6022-merge-rename.sh
> > > > +++ b/t/t6022-merge-rename.sh
> > > > @@ -242,12 +242,23 @@ test_expect_success 'merge of identical changes in a renamed file' '
> > > > rm -f A M N &&
> > > > git reset --hard &&
> > > > git checkout change+rename &&
> > > > +
> > > > + test-tool chmtime =31337 B &&
> > > > + test-tool chmtime --get B >old-mtime &&
> > >
> > > Nit: I think it's possible to change the mtime and print it in a
> > > single invocation with:
> > >
> > > test-tool chmtime --get =1234 file
> >
> > Oh, cool.
> >
> > > > GIT_MERGE_VERBOSITY=3 git merge change >out &&
> > >
> > > Nit: The output of 'git merge' is still redirected to a file, but ...
> > >
> > > > - test_i18ngrep "^Skipped B" out &&
> > >
> > > ... the only command looking at the output is now removed.
> >
> > Indeed.
> >
> > > > + test-tool chmtime --get B >new-mtime &&
> > > > + test_cmp old-mtime new-mtime &&
> > > > +
> > > > git reset --hard HEAD^ &&
> > > > git checkout change &&
> > > > +
> > > > + test-tool chmtime =-1 M &&
> > > > + test-tool chmtime --get M >old-mtime &&
> > > > GIT_MERGE_VERBOSITY=3 git merge change+rename >out &&
> > > > - test_i18ngrep ! "^Skipped B" out
> > >
> > > Likewise.
> > >
> > > > + test-tool chmtime --get B >new-mtime &&
> > > > + test $(cat old-mtime) -lt $(cat new-mtime)
> > >
> > > I saw this test fail today in one of my custom CI builds:
> > >
> > > +git checkout change
> > > Switched to branch 'change'
> > > +test-tool chmtime =-1 M
> > > +test-tool chmtime --get M
> > > +GIT_MERGE_VERBOSITY=3 git merge change+rename
> > > +test-tool chmtime --get B
> > > +cat old-mtime
> > > +cat new-mtime
> > > +test 1583967731 -lt 1583967731
> > > error: last command exited with $?=1
> > > not ok 12 - merge of identical changes in a renamed file
> > >
> > > The contents of 'out', i.e. the output of the 'git merge' command
> > > before the failure is:
> > >
> > > Auto-merging B
> > > Merge made by the 'recursive' strategy.
> > > A => B | 0
> > > 1 file changed, 0 insertions(+), 0 deletions(-)
> > > rename A => B (100%)
> > >
> > > This is a rare failure, this is the first time I saw it, and to make
> > > things worse, this one time it happened on big-endian and with all the
> > > GIT_TEST_* knobs enabled.
> > >
> > > https://travis-ci.org/github/szeder/git-cooking-topics-for-travis-ci/jobs/661294571#L4020
> >
> > This is very troubling. The workflow is basically:
> > - Manually set the mtime to a file to something old (I happened to
> > pick 1 second before now, but picking something from 1970 would have
> > been fine too).
> > - Run a merge which is known to need to overwrite the file. Your
> > output ("Auto-merging B") suggests that we should have been in such a
> > case.
> > - Verify that the file was actually updated as expected. Since the
> > OS is supposed to update the mtime when it writes the file, it should
> > have set it to something recent, i.e. something *different* than what
> > it had before.
> >
> > So, now I'm left wondering how the mtime possibly could have been not
> > updated. Maybe the file wasn't actually written? (But if so, why
> > didn't other people see the failure? Or your stress runs not see it?)
> > Or maybe it was written but all file contents and metadata were
> > delayed in writing to disk such that a subsequent command still sees
> > the old file?? Or maybe it was written but the mtime update was
> > delayed and the test was able to check it in that intermediate
> > state??? Or perhaps the mtime check before the merge raced with the
> > setting of the mtime backwards and got the mtime before it was
> > rewound????
> >
> > I don't have a plausible scenario under which any of these should be
> > possible; I'm at a loss.
>
> Hmm. Maybe leap seconds, or clock updates via ntp at an unfortunate
> time?
I'm now fairly confident that 'git merge' is OK, and suspect that it's
an issue with Travis CI's s390x environment (multi-architecture
support is an alpha-stage feature).
I kicked off a build that only runs 't6022 --stress -r 1,12', and it
failed with the same error on s390x fairly quickly, but haven't failed
in any of our "standard" CI jobs until the jobs timeouted.
https://travis-ci.org/github/szeder/git/jobs/661647673#L2084
Then I kicked off a build to run the test below with --stress:
test_expect_success 'test' '
touch file &&
old=$(test-tool chmtime --get =-1 file) &&
touch file &&
new=$(test-tool chmtime --get file) &&
test $old -lt $new
'
This failed fairly quickly with the same error on s390x as well.
https://travis-ci.org/github/szeder/git/jobs/661654844#L1275
So I think 'git merge' should be okay, because the failure could be
triggered without it as well.
> Perhaps just setting the "old" time to something more than one
> second in the past would avoid this?
>
> Anyone have a clue if this is a useful guess or not?
I kicked off a build where I set an older timestamp ('=-10' instead of
'=-1'), to see what happens, but the s390x job in that build just
doesn't want to start... (alpha feature? :) Anyway, the job's output
should eventually be available here, will try to check back tomorrow:
https://travis-ci.org/github/szeder/git/jobs/661657781
next prev parent reply other threads:[~2020-03-12 20:02 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-27 0:14 [PATCH 0/5] Testcase cleanups (merge related) Elijah Newren via GitGitGadget
2020-02-27 0:14 ` [PATCH 1/5] t602[1236], t6034: modernize test formatting Elijah Newren via GitGitGadget
2020-02-27 0:14 ` [PATCH 2/5] t6020, t6022, t6035: update merge tests to use test helper functions Elijah Newren via GitGitGadget
2020-02-27 0:14 ` [PATCH 3/5] t3035: prefer test_must_fail to bash negation for git commands Elijah Newren via GitGitGadget
2020-02-27 0:14 ` [PATCH 4/5] t6022, t6046: test expected behavior instead of testing a proxy for it Elijah Newren via GitGitGadget
2020-03-12 13:20 ` SZEDER Gábor
2020-03-12 16:48 ` Elijah Newren
2020-03-12 17:35 ` Elijah Newren
2020-03-12 20:01 ` SZEDER Gábor [this message]
2020-03-13 17:17 ` SZEDER Gábor
2020-03-13 17:45 ` Elijah Newren
2020-03-13 17:12 ` SZEDER Gábor
2020-03-13 17:18 ` Elijah Newren
2020-03-13 17:30 ` SZEDER Gábor
2020-03-13 18:11 ` Elijah Newren
2020-02-27 0:14 ` [PATCH 5/5] t6020: new test with interleaved lexicographic ordering of directories Elijah Newren via GitGitGadget
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