path: root/split-index.c
diff options
authorSZEDER Gábor <>2018-10-11 09:43:09 (GMT)
committerJunio C Hamano <>2018-10-11 22:23:29 (GMT)
commit5581a019ba0a53ea2b69d477d395590f7aba257c (patch)
tree54a89bf41743e3c571126d08eed150b438e3074f /split-index.c
parente3d837989ef6b98ce6822145322d9e3d250a5b6f (diff)
split-index: smudge and add racily clean cache entries to split index
Ever since the split index feature was introduced [1], refreshing a split index is prone to a variant of the classic racy git problem. Consider the following sequence of commands updating the split index when the shared index contains a racily clean cache entry, i.e. an entry whose cached stat data matches with the corresponding file in the worktree and the cached mtime matches that of the index: echo "cached content" >file git update-index --split-index --add file echo "dirty worktree" >file # size stays the same! # ... wait ... git update-index --add other-file Normally, when a non-split index is updated, then do_write_index() (the function responsible for writing all kinds of indexes, "regular", split, and shared) recognizes racily clean cache entries, and writes them with smudged stat data, i.e. with file size set to 0. When subsequent git commands read the index, they will notice that the smudged stat data doesn't match with the file in the worktree, and then go on to check the file's content and notice its dirtiness. In the above example, however, in the second 'git update-index' prepare_to_write_split_index() decides which cache entries stored only in the shared index should be replaced in the new split index. Alas, this function never looks out for racily clean cache entries, and since the file's stat data in the worktree hasn't changed since the shared index was written, it won't be replaced in the new split index. Consequently, do_write_index() doesn't even get this racily clean cache entry, and can't smudge its stat data. Subsequent git commands will then see that the index has more recent mtime than the file and that the (not smudged) cached stat data still matches with the file in the worktree, and, ultimately, will erroneously consider the file clean. Modify prepare_to_write_split_index() to recognize racily clean cache entries, and mark them to be added to the split index. Note that there are two places where it should check raciness: first those cache entries that are only stored in the shared index, and then those that have been copied by unpack_trees() from the shared index while it constructed a new index. This way do_write_index() will get these racily clean cache entries as well, and will then write them with smudged stat data to the new split index. This change makes all tests in '' pass, so flip the two 'test_expect_failure' tests to success. Also add the '#' (as in nr. of trial) to those tests' description that were omitted when the tests expected failure. Note that after this change if the index is split when it contains a racily clean cache entry, then a smudged cache entry will be written both to the new shared and to the new split indexes. This doesn't affect regular git commands: as far as they are concerned this is just an entry in the split index replacing an outdated entry in the shared index. It did affect a few tests in '', though, because they actually check which entries are stored in the split index; a previous patch in this series has already made the necessary adjustments in 't1700'. And racily clean cache entries and index splitting are rare enough to not worry about the resulting duplicated smudged cache entries, and the additional complexity required to prevent them is not worth it. Several tests failed occasionally when the test suite was run with 'GIT_TEST_SPLIT_INDEX=yes'. Here are those that I managed to trace back to this racy split index problem, starting with those failing more frequently, with a link to a failing Travis CI build job for each. The highlighted line [2] shows when the racy file was written, which is not always in the failing test but in a preceeding setup test. There might be others, e.g. perhaps '' and others using '', but I couldn't confirm yet. [1] In the branch leading to the merge commit v2.1.0-rc0~45 (Merge branch 'nd/split-index', 2014-07-16). [2] Note that those highlighted lines are in the 'after failure' fold, and your browser might unhelpfully fold it up before you could take a good look. Signed-off-by: SZEDER Gábor <> Signed-off-by: Junio C Hamano <>
Diffstat (limited to 'split-index.c')
1 files changed, 41 insertions, 1 deletions
diff --git a/split-index.c b/split-index.c
index 187b910..875f538 100644
--- a/split-index.c
+++ b/split-index.c
@@ -259,8 +259,39 @@ void prepare_to_write_split_index(struct index_state *istate)
ce->ce_flags |= CE_MATCHED; /* or "shared" */
base = si->base->cache[ce->index - 1];
- if (ce == base)
+ if (ce == base) {
+ /* The entry is present in the shared index. */
+ if (ce->ce_flags & CE_UPDATE_IN_BASE) {
+ /*
+ * Already marked for inclusion in
+ * the split index, either because
+ * the corresponding file was
+ * modified and the cached stat data
+ * was refreshed, or because there
+ * is already a replacement entry in
+ * the split index.
+ * Nothing more to do here.
+ */
+ } else if (!ce_uptodate(ce) &&
+ is_racy_timestamp(istate, ce)) {
+ /*
+ * A racily clean cache entry stored
+ * only in the shared index: it must
+ * be added to the split index, so
+ * the subsequent do_write_index()
+ * can smudge its stat data.
+ */
+ ce->ce_flags |= CE_UPDATE_IN_BASE;
+ } else {
+ /*
+ * The entry is only present in the
+ * shared index and it was not
+ * refreshed.
+ * Just leave it there.
+ */
+ }
+ }
if (ce->ce_namelen != base->ce_namelen ||
strcmp(ce->name, base->name)) {
ce->index = 0;
@@ -281,6 +312,15 @@ void prepare_to_write_split_index(struct index_state *istate)
* the split index.
* Nothing to do.
+ } else if (!ce_uptodate(ce) &&
+ is_racy_timestamp(istate, ce)) {
+ /*
+ * A copy of a racily clean cache entry from
+ * the shared index. It must be added to
+ * the split index, so the subsequent
+ * do_write_index() can smudge its stat data.
+ */
+ ce->ce_flags |= CE_UPDATE_IN_BASE;
} else {
* Thoroughly compare the cached data to see