On Sat, Feb 19 2022, Elijah Newren via GitGitGadget wrote:
> From: Elijah Newren <newren@xxxxxxxxx>
>
> detect_and_process_renames() detects renames on both sides of history
> and then combines these into a single diff_queue_struct. The combined
> diff_queue_struct needs to be able to hold the renames found on either
> side, and since it knows the (maximum) size it needs, it pre-emptively
> grows the array to the appropriate size:
>
> ALLOC_GROW(combined.queue,
> renames->pairs[1].nr + renames->pairs[2].nr,
> combined.alloc);
>
> It then collects the items from each side:
>
> collect_renames(opt, &combined, MERGE_SIDE1, ...)
> collect_renames(opt, &combined, MERGE_SIDE2, ...)
>
> Note, though, that collect_renames() sometimes determines that some
> pairs are unnecessary and does not include them in the combined array.
> When it is done, detect_and_process_renames() frees this memory:
>
> if (combined.nr) {
> ...
> free(combined.queue);
> }
>
> The problem is that sometimes even when there are pairs, none of them are
> necessary. Instead of checking combined.nr, we should check
> combined.alloc. Doing so fixes the following memory leak, as reported
> by valgrind:
>
> ==PID== 192 bytes in 1 blocks are definitely lost in loss record 107 of 134
> ==PID== at 0xADDRESS: malloc
> ==PID== by 0xADDRESS: realloc
> ==PID== by 0xADDRESS: xrealloc (wrapper.c:126)
> ==PID== by 0xADDRESS: detect_and_process_renames (merge-ort.c:3134)
> ==PID== by 0xADDRESS: merge_ort_nonrecursive_internal (merge-ort.c:4610)
> ==PID== by 0xADDRESS: merge_ort_internal (merge-ort.c:4709)
> ==PID== by 0xADDRESS: merge_incore_recursive (merge-ort.c:4760)
> ==PID== by 0xADDRESS: merge_ort_recursive (merge-ort-wrappers.c:57)
> ==PID== by 0xADDRESS: try_merge_strategy (merge.c:753)
> ==PID== by 0xADDRESS: cmd_merge (merge.c:1676)
> ==PID== by 0xADDRESS: run_builtin (git.c:461)
> ==PID== by 0xADDRESS: handle_builtin (git.c:713)
> ==PID== by 0xADDRESS: run_argv (git.c:780)
> ==PID== by 0xADDRESS: cmd_main (git.c:911)
> ==PID== by 0xADDRESS: main (common-main.c:52)
>
> Reported-by: Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx>
> Signed-off-by: Elijah Newren <newren@xxxxxxxxx>
> ---
> merge-ort.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/merge-ort.c b/merge-ort.c
> index d85b1cd99e9..4f5abc558c5 100644
> --- a/merge-ort.c
> +++ b/merge-ort.c
> @@ -3175,7 +3175,7 @@ simple_cleanup:
> free(renames->pairs[s].queue);
> DIFF_QUEUE_CLEAR(&renames->pairs[s]);
> }
> - if (combined.nr) {
> + if (combined.alloc) {
> int i;
> for (i = 0; i < combined.nr; i++)
> pool_diff_free_filepair(&opt->priv->pool,
This looks correct in that it'll work, but I still don't get why the
pre-image or post-image is going through this indirection of checking
"alloc" at all. Wouldn't this be correct & more straightforward (the
memset part is optional, just did it for good measure)?:
diff --git a/merge-ort.c b/merge-ort.c
index 40ae4dc4e92..a01f28586a1 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -3092,12 +3092,12 @@ static int detect_and_process_renames(struct merge_options *opt,
struct tree *side1,
struct tree *side2)
{
- struct diff_queue_struct combined;
+ struct diff_queue_struct combined = { 0 };
struct rename_info *renames = &opt->priv->renames;
int need_dir_renames, s, clean = 1;
unsigned detection_run = 0;
+ int i;
- memset(&combined, 0, sizeof(combined));
if (!possible_renames(renames))
goto cleanup;
@@ -3181,13 +3181,10 @@ static int detect_and_process_renames(struct merge_options *opt,
free(renames->pairs[s].queue);
DIFF_QUEUE_CLEAR(&renames->pairs[s]);
}
- if (combined.alloc) {
- int i;
- for (i = 0; i < combined.nr; i++)
- pool_diff_free_filepair(&opt->priv->pool,
- combined.queue[i]);
- free(combined.queue);
- }
+
+ for (i = 0; i < combined.nr; i++)
+ pool_diff_free_filepair(&opt->priv->pool, combined.queue[i]);
+ free(combined.queue);
return clean;
}
