From: Derrick Stolee <stolee@gmail.com>
Date: Wed, 12 Sep 2018 13:08:28 GMT
Subject: Re: [PATCH v2 17/18] commit-reach: make can_all_from_reach... linear
Message-ID: <0bf9103c-9377-506b-7ad7-e5273d8e94fc@gmail.com>
In-Reply-To: <20180912042938.GA15876@sigill.intra.peff.net>

On 9/12/2018 12:29 AM, Jeff King wrote:
> On Wed, Sep 12, 2018 at 12:14:25AM -0400, Jeff King wrote:
>
>>> +	ALLOC_ARRAY(list, from->nr);
>>>   	for (i = 0; i < from->nr; i++) {
>>> -		struct object *from_one = from->objects[i].item;
>>> +		list[i] = (struct commit *)from->objects[i].item;
>> Some of the objects in my array are not commits, but rather tags, so
>> this is a bogus cast.
>>
>> You can see that the original code peeled them and threw away
>> non-commits:
>>
>>>   
>>> -		if (from_one->flags & assign_flag)
>>> -			continue;
>>> -		from_one = deref_tag(the_repository, from_one, "a from object", 0);
>>> -		if (!from_one || from_one->type != OBJ_COMMIT) {
>>> -			/* no way to tell if this is reachable by
>>> -			 * looking at the ancestry chain alone, so
>>> -			 * leave a note to ourselves not to worry about
>>> -			 * this object anymore.
>>> -			 */
>>> -			from->objects[i].item->flags |= assign_flag;
>>> -			continue;
>>> -		}
>> So presumably we'd need to do something similar.
> This patch seems to fix it for me. It's more or less a reversion of the
> hunk above, though I didn't dig into whether I'm violating some other
> assumption in your new code.
>
> I think this function leaks "list" both from the location I noted here,
> as well as from normal exit
Thanks for the report and the fix. I'll try to create  test that 
demonstrates this and then push up a full patch.
> ---
>   commit-reach.c | 25 ++++++++++++++++++-------
>   1 file changed, 18 insertions(+), 7 deletions(-)
>
> diff --git a/commit-reach.c b/commit-reach.c
> index 622eeb313d..abe90a2f55 100644
> --- a/commit-reach.c
> +++ b/commit-reach.c
> @@ -547,20 +547,31 @@ int can_all_from_reach_with_flag(struct object_array *from,
>   {
>   	struct commit **list = NULL;
>   	int i;
> +	int nr_commits;
>   	int result = 1;
>   
>   	ALLOC_ARRAY(list, from->nr);
> +	nr_commits = 0;
>   	for (i = 0; i < from->nr; i++) {
> -		list[i] = (struct commit *)from->objects[i].item;
> +		struct object *from_one = from->objects[i].item;
>   
> -		if (parse_commit(list[i]) ||
> -		    list[i]->generation < min_generation)
> -			return 0;
> +		from_one = deref_tag(the_repository, from_one,
> +				     "a from object", 0);
> +		if (!from_one || from_one->type != OBJ_COMMIT) {
> +			from->objects[i].item->flags |= assign_flag;
> +			continue;
> +		}
> +
> +		list[nr_commits] = (struct commit *)from_one;
> +		if (parse_commit(list[nr_commits]) ||
> +		    list[nr_commits]->generation < min_generation)
> +			return 0; /* is this a leak? */
> +		nr_commits++;
>   	}
>   
> -	QSORT(list, from->nr, compare_commits_by_gen);
> +	QSORT(list, nr_commits, compare_commits_by_gen);
>   
> -	for (i = 0; i < from->nr; i++) {
> +	for (i = 0; i < nr_commits; i++) {
>   		/* DFS from list[i] */
>   		struct commit_list *stack = NULL;
>   
> @@ -603,7 +614,7 @@ int can_all_from_reach_with_flag(struct object_array *from,
>   	}
>   
>   cleanup:
> -	for (i = 0; i < from->nr; i++) {
> +	for (i = 0; i < nr_commits; i++) {
>   		clear_commit_marks(list[i], RESULT);
>   		clear_commit_marks(list[i], assign_flag);
>   	}