From: Johannes Schindelin <johannes.schindelin@xxxxxx> In 56c6910028a (fsmonitor: change last update timestamp on the index_state to opaque token, 2020-01-07), we forgot to adjust the part of `unpack_trees()` that copies the FSMonitor "last-update" information that we copy from the source index to the result index since 679f2f9fdd2 (unpack-trees: skip stat on fsmonitor-valid files, 2019-11-20). Since the "last-update" information is no longer a 64-bit number, but a free-form string that has been allocated, we need to duplicate it rather than just copying it. This is important because there _are_ cases when `unpack_trees()` will perform a oneway merge that implicitly calls `refresh_fsmonitor()` (which will allocate that "last-update" token). This happens _after_ that token was copied into the result index. However, we _then_ call `check_updates()` on that index, which will _also_ call `refresh_fsmonitor()`, accessing the "last-update" string, which by now would be released already. In the instance that lead to this patch, this caused a segmentation fault during a lengthy, complicated rebase involving the todo command `reset` that (crucially) had to updated many files. Unfortunately, it seems very hard to trigger that crash, therefore this patch is not accompanied by a regression test. Signed-off-by: Johannes Schindelin <johannes.schindelin@xxxxxx> --- unpack-trees.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/unpack-trees.c b/unpack-trees.c index 2399b6818be6..63e3d961b378 100644 --- a/unpack-trees.c +++ b/unpack-trees.c @@ -1544,8 +1544,8 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options o->merge_size = len; mark_all_ce_unused(o->src_index); - if (o->src_index->fsmonitor_last_update) - o->result.fsmonitor_last_update = o->src_index->fsmonitor_last_update; + o->result.fsmonitor_last_update = + xstrdup_or_null(o->src_index->fsmonitor_last_update); /* * Sparse checkout loop #1: set NEW_SKIP_WORKTREE on existing entries -- gitgitgadget
