Re: [PATCH 1/1] fsmonitor: skip sanity check if the index is split

>
> On Fri, Nov 08, 2019 at 07:09:20AM +0000, Utsav Shah via GitGitGadget wrote:
> > The checks added in 3444ec2eb2 ("fsmonitor: don't fill bitmap with
> > entries to be removed", 2019-10-11), to ensure that the
> > fsmonitor_dirty bitmap does not have more bits than the index
> > do not play well with the split index.
> >
> > git update-index --fsmonitor --split-index calls write_locked_index
> > which calls write_shared_index as well as write_split_index.
> > The first call fills up the fsmonitor_dirty bitmap,
> > and the second modifies the index such that istate->cache_nr is zero and
> > this assert is hit.
>
> Just to make sure that we are on the same page, is this the one?
>
>   BUG: fsmonitor.c:88: fsmonitor_dirty has more entries than the index (102 > 1)
>

> > The test written does reproduce the error, but only flakily. There is
> > limited difference with GIT_TEST_FSMONITOR=fsmonitor-all or
> > GIT_TEST_FSMONITOR=fsmonitor-watchman, so the flakiness might come from
> > somewhere else, which I haven't tracked down.
> >
> > The test also requires checkout of a new branch, and checking out back
> > to master.
>
> It doesn't; see below.
>
> > It's clear that the index gets into some poor state through
> > these operations, and there is a deeper bug somewhere.
> >
> > At the very least, this patch mitigates an over-eager check for split
> > index users while maintaining good invariants for the standard case.
> > Also, I haven't been able to reproduce this with "standard" user
> > commands, like status/checkout/stash, so the blast radius seems limited.
> >
> > Helped-by: Kevin Willford <kewillf@microsoft.com>
> > Helped-by: Junio C Hamano <gitster@pobox.com>
> > Signed-off-by: Utsav Shah <utsav@dropbox.com>
> > ---
>
> > diff --git a/t/t7519-status-fsmonitor.sh b/t/t7519-status-fsmonitor.sh
> > index d8df990972..b5029eff3e 100755
> > --- a/t/t7519-status-fsmonitor.sh
> > +++ b/t/t7519-status-fsmonitor.sh
> > @@ -371,4 +371,27 @@ test_expect_success 'status succeeds after staging/unstaging ' '
> >       )
> >  '
> >
> > +# Git will only split indices if we have a bunch of files created,
> > +# so that prep work of creating a few hundred files is required.
>
> 'git update-index --split-index' splits the index no matter what; it
> even splits an empty index.
>
> > +# Note that this test doesn't fail determinstically without
> > +# its corresponding bugfix.
> > +test_expect_success 'update-index succeeds after staging with split index' '
> > +     test_create_repo fsmonitor-stage-split &&
> > +     (
> > +             cd fsmonitor-stage-split &&
> > +             test_commit initial &&
> > +             files=$(test_seq 1 100) &&
> > +             echo "hello world" > file &&
> > +             touch $files &&
> > +             git add -A &&
> > +             git commit -m "next" &&
> > +             git config core.fsmonitor "$TEST_DIRECTORY/t7519/fsmonitor-watchman" &&
> > +             echo "hello world" > file &&
> > +             git checkout -b new-branch &&
> > +             git checkout master &&
> > +             echo hello >> file &&
> > +             git update-index --split-index --untracked-cache --fsmonitor
> > +     )
> > +'
>
> I could reproduce the failure with '-r 30 --stress' relatively easily
> [1], but with those options I could shave off a lot from this test:
>
>         test_create_repo fsmonitor-stage-split &&
>         (
>                 cd fsmonitor-stage-split &&
>                 >tracked &&
>                 git add tracked &&
>                 git config core.fsmonitor
>                 "$TEST_DIRECTORY/t7519/fsmonitor-watchman" &&
>                 >untracked &&
>                 git update-index --split-index --untracked-cache --fsmonitor
>         )
>
> and could still trigger the failure:
>
>   + git update-index --split-index --untracked-cache --fsmonitor
>   open2: exec of watchman -j failed at /home/szeder/src/git/t/t7519/fsmonitor-watchman line 47.
>   BUG: fsmonitor.c:88: fsmonitor_dirty has more entries than the index (1 > 0)
>
>
> [1] There is a quite expensive lazy prereq evaluation outside of
>     'test_expect_*' that I disabled it with the following for
>     speedier stress testing:
>
> diff --git a/t/t7519-status-fsmonitor.sh b/t/t7519-status-fsmonitor.sh
> index 997d5fb349..103520415d 100755
> --- a/t/t7519-status-fsmonitor.sh
> +++ b/t/t7519-status-fsmonitor.sh
> @@ -50,8 +50,7 @@ write_integration_script () {
>  }
>
>  test_lazy_prereq UNTRACKED_CACHE '
> -       { git update-index --test-untracked-cache; ret=$?; } &&
> -       test $ret -ne 1
> +       true
>  '
>
>  test_expect_success 'setup' '