Re: [PATCH 05/11] submodule-config: avoid memory leak

From: Glen Choo <chooglen@google.com>
To: Junio C Hamano <gitster@pobox.com>,
	Johannes Schindelin via GitGitGadget <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org, Johannes Schindelin <johannes.schindelin@gmx.de>
Subject: Re: [PATCH 05/11] submodule-config: avoid memory leak
Date: Thu, 16 Jun 2022 11:09:07 -0700	[thread overview]
Message-ID: <kl6lpmj84h18.fsf@chooglen-macbookpro.roam.corp.google.com> (raw)
In-Reply-To: <xmqqmtedw7fm.fsf@gitster.g>

Junio C Hamano <gitster@pobox.com> writes:

> "Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>
> writes:
>
>> From: Johannes Schindelin <johannes.schindelin@gmx.de>
>>
>> In 961b130d20c9 (branch: add --recurse-submodules option for branch
>> creation, 2022-01-28), a funny pattern was introduced where first some
>> struct is `xmalloc()`ed, then we resize an array whose element type is
>> the same struct, and then the first struct's contents are copied into
>> the last element of that array.
>
> Sigh.  The original is butt ugly, with this strange pattern and
> structure assignments etc.  I wonder how something like this slipped
> through our reviews.

Gah, I have no excuses for bad code I've already written, I can only
strive to write better code next time.

Thanks Johannes for spotting and fixing this.

> I wonder if it would help for me to stop trusting reviews by less
> experienced reviewers too much, and instead give sanity checks to
> more patches myself from now on, but I certainly cannot afford the
> time and my mental health to do so for all the patches X-<.

I seem to recall that this was reviewed by fairly experienced folks. I'm
guessing it slipped through due to reviewer fatigue, which might be a
good argument for adding more tooling to lighten reviewer load/patch up
the gaps.

>
> Will queue.
>
>>  		if (S_ISGITLINK(name_entry->mode) &&
>>  		    is_tree_submodule_active(r, root_tree, tree_path)) {
>> -			st_entry = xmalloc(sizeof(*st_entry));
>> +			ALLOC_GROW(out->entries, out->entry_nr + 1,
>> +				   out->entry_alloc);
>> +			st_entry = &out->entries[out->entry_nr++];
>> +
>>  			st_entry->name_entry = xmalloc(sizeof(*st_entry->name_entry));
>>  			*st_entry->name_entry = *name_entry;
>>  			st_entry->submodule =
>> @@ -766,9 +769,6 @@ static void traverse_tree_submodules(struct repository *r,
>>  						root_tree))
>>  				FREE_AND_NULL(st_entry->repo);
>>  
>> -			ALLOC_GROW(out->entries, out->entry_nr + 1,
>> -				   out->entry_alloc);
>> -			out->entries[out->entry_nr++] = *st_entry;
>>  		} else if (S_ISDIR(name_entry->mode))
>>  			traverse_tree_submodules(r, root_tree, tree_path,
>>  						 &name_entry->oid, out);