Subject: Re: [PATCH v3] diff-lib: Fix check_removed when fsmonitor is on

From: Junio C Hamano <[email-masked]>
Date: Mon, 11 Sep 2023 15:53:32 -0700

Josip Sokcevic <[email-masked]> writes:

> git-diff-index may return incorrect deleted entries when fsmonitor is used in a
> repository with git submodules. This can be observed on Mac machines, but it
> can affect all other supported platforms too.
>
> If fsmonitor is used, `stat *st` is not initialized if cache_entry has
> CE_FSMONITOR_VALID set. But, there are three call sites that rely on stat
> afterwards, which can result in incorrect results.
>
> This change partially reverts commit 4f3d6d0.
>
> Signed-off-by: Josip Sokcevic <[email-masked]>
> ---
>  diff-lib.c                   | 12 ++++++------
>  t/t7527-builtin-fsmonitor.sh |  5 +++++
>  2 files changed, 11 insertions(+), 6 deletions(-)

This certainly is more "complete" if simpler than the previous one
;-)

In the longer term, we would probably want to enable optimization
using what fsmonitor knows, but as we have seen in the review on
the previous round, this code needs a bit more work than the
original we are reverting here to get it right, and in the shorter
term, hopefully this would do.

Thanks.

> diff --git a/diff-lib.c b/diff-lib.c
> index d8aa777a73..5848e4f9ca 100644
> --- a/diff-lib.c
> +++ b/diff-lib.c
> @@ -36,14 +36,14 @@
>   * exists for ce that is a submodule -- it is a submodule that is not
>   * checked out).  Return negative for an error.
>   */
> -static int check_removed(const struct index_state *istate, const struct cache_entry *ce, struct stat *st)
> +static int check_removed(const struct cache_entry *ce, struct stat *st)
>  {
> -	assert(is_fsmonitor_refreshed(istate));
> -	if (!(ce->ce_flags & CE_FSMONITOR_VALID) && lstat(ce->name, st) < 0) {
> +	if (lstat(ce->name, st) < 0) {
>  		if (!is_missing_file_error(errno))
>  			return -1;
>  		return 1;
>  	}
> +
>  	if (has_symlink_leading_path(ce->name, ce_namelen(ce)))
>  		return 1;
>  	if (S_ISDIR(st->st_mode)) {
> @@ -149,7 +149,7 @@ void run_diff_files(struct rev_info *revs, unsigned int option)
>  			memset(&(dpath->parent[0]), 0,
>  			       sizeof(struct combine_diff_parent)*5);
>  
> -			changed = check_removed(istate, ce, &st);
> +			changed = check_removed(ce, &st);
>  			if (!changed)
>  				wt_mode = ce_mode_from_stat(ce, st.st_mode);
>  			else {
> @@ -229,7 +229,7 @@ void run_diff_files(struct rev_info *revs, unsigned int option)
>  		} else {
>  			struct stat st;
>  
> -			changed = check_removed(istate, ce, &st);
> +			changed = check_removed(ce, &st);
>  			if (changed) {
>  				if (changed < 0) {
>  					perror(ce->name);
> @@ -303,7 +303,7 @@ static int get_stat_data(const struct index_state *istate,
>  	if (!cached && !ce_uptodate(ce)) {
>  		int changed;
>  		struct stat st;
> -		changed = check_removed(istate, ce, &st);
> +		changed = check_removed(ce, &st);
>  		if (changed < 0)
>  			return -1;
>  		else if (changed) {
> diff --git a/t/t7527-builtin-fsmonitor.sh b/t/t7527-builtin-fsmonitor.sh
> index 0c241d6c14..78503158fd 100755
> --- a/t/t7527-builtin-fsmonitor.sh
> +++ b/t/t7527-builtin-fsmonitor.sh
> @@ -809,6 +809,11 @@ my_match_and_clean () {
>  		status --porcelain=v2 >actual.without &&
>  	test_cmp actual.with actual.without &&
>  
> +	git -C super --no-optional-locks diff-index --name-status HEAD >actual.with &&
> +	git -C super --no-optional-locks -c core.fsmonitor=false \
> +		diff-index --name-status HEAD >actual.without &&
> +	test_cmp actual.with actual.without &&
> +
>  	git -C super/dir_1/dir_2/sub reset --hard &&
>  	git -C super/dir_1/dir_2/sub clean -d -f
>  }