Currently, all callers of unpack_trees() set o->src_index == o->dst_index.
Since we create a temporary index in o->result, then discard o->dst_index
and overwrite it with o->result, when o->src_index == o->dst_index it is
safe to just reuse o->src_index's split_index for o->result. However,
o->src_index and o->dst_index are specified separately in order to allow
callers to have these be different. In such a case, reusing
o->src_index's split_index for o->result will cause the split_index to be
shared. If either index then has entries replaced or removed, it will
result in the other index referring to free()'d memory.
Signed-off-by: Elijah Newren <newren@xxxxxxxxx>
---
I still haven't wrapped my head around the split_index stuff entirely, so
it's possible that
- the performance optimization isn't even valid when src == dst. Could
the original index be different enough from the result that we don't
want its split_index?
- there's a better, more performant fix or there is some way to actually
share a split_index between two independent index_state objects.
However, with this fix, all the tests pass both normally and under
GIT_TEST_SPLIT_INDEX=DareISayYes. Without this patch, when
GIT_TEST_SPLIT_INDEX is set, my directory rename detection series will fail
several tests, as reported by SZEDER.
unpack-trees.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/unpack-trees.c b/unpack-trees.c
index 79fd97074e..b670415d4c 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -1284,9 +1284,20 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
o->result.timestamp.sec = o->src_index->timestamp.sec;
o->result.timestamp.nsec = o->src_index->timestamp.nsec;
o->result.version = o->src_index->version;
- o->result.split_index = o->src_index->split_index;
- if (o->result.split_index)
+ if (!o->src_index->split_index) {
+ o->result.split_index = NULL;
+ } else if (o->src_index == o->dst_index) {
+ /*
+ * o->dst_index (and thus o->src_index) will be discarded
+ * and overwritten with o->result at the end of this function,
+ * so just use src_index's split_index to avoid having to
+ * create a new one.
+ */
+ o->result.split_index = o->src_index->split_index;
o->result.split_index->refcount++;
+ } else {
+ o->result.split_index = init_split_index(&o->result);
+ }
hashcpy(o->result.sha1, o->src_index->sha1);
o->merge_size = len;
mark_all_ce_unused(o->src_index);
--
2.17.0.296.gaac25b4b81
