Re: [PATCH v2 1/2] merge-ort: fix small memory leak in detect_and_process_renames()

> From: Elijah Newren <newren@gmail.com>
>
> 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, just remove the
> if-check; free() knows to skip NULL pointers.  This change 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@gmail.com>
> Signed-off-by: Elijah Newren <newren@gmail.com>
> ---
>  merge-ort.c | 15 +++++----------
>  1 file changed, 5 insertions(+), 10 deletions(-)
>
> diff --git a/merge-ort.c b/merge-ort.c
> index d85b1cd99e9..3d7f9feb6f7 100644
> --- a/merge-ort.c
> +++ b/merge-ort.c
> @@ -3086,12 +3086,11 @@ 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;
> +	int need_dir_renames, s, i, clean = 1;
>  	unsigned detection_run = 0;
>  
> -	memset(&combined, 0, sizeof(combined));
>  	if (!possible_renames(renames))
>  		goto cleanup;
>  
> @@ -3175,13 +3174,9 @@ simple_cleanup:
>  		free(renames->pairs[s].queue);
>  		DIFF_QUEUE_CLEAR(&renames->pairs[s]);
>  	}
> -	if (combined.nr) {
> -		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;
>  }