[PATCH 0/1] fsmonitor: skip sanity check if the index is split

["Utsav Shah via GitGitGadget" <gitgitgadget@gmail.com>]

The checks added in 3444ec2 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.

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'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 [kewillf@microsoft.com]
Helped-by: Junio C Hamano gitster@pobox.com [gitster@pobox.com]
Signed-off-by: Utsav Shah utsav@dropbox.com [utsav@dropbox.com]

Utsav Shah (1):
  fsmonitor: skip sanity check if the index is split

 fsmonitor.c                 |  8 ++++----
 t/t7519-status-fsmonitor.sh | 23 +++++++++++++++++++++++
 2 files changed, 27 insertions(+), 4 deletions(-)


base-commit: 566a1439f6f56c2171b8853ddbca0ad3f5098770
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-458%2FUtsav2%2Fsplit-fix-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-458/Utsav2/split-fix-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/458
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