Re: [PATCH Outreachy] mru: use double-linked list from list.h

On Fri, Sep 29, 2017 at 09:18:11AM +0200, Christian Couder wrote:

On Fri, Sep 29, 2017 at 12:42 AM, Jeff King [off-list ref] wrote:

quoted

On Thu, Sep 28, 2017 at 08:38:39AM +0000, Olga Telezhnaya wrote:

quoted

diff --git a/packfile.c b/packfile.c
index f69a5c8d607af..ae3b0b2e9c09a 100644
--- a/packfile.c
+++ b/packfile.c

@@ -876,6 +876,7 @@ void prepare_packed_git(void)
      for (alt = alt_odb_list; alt; alt = alt->next)
              prepare_packed_git_one(alt->path, 0);
      rearrange_packed_git();
+     INIT_LIST_HEAD(&packed_git_mru.list);
      prepare_packed_git_mru();
      prepare_packed_git_run_once = 1;
 }

I was thinking on this hunk a bit more, and I think it's not quite
right.

The prepare_packed_git_mru() function will clear the mru list and then
re-add each item from the packed_git list. But by calling
INIT_LIST_HEAD() here, we're effectively clearing the packed_git_mru
list, and we end up leaking whatever was on the list before.

The current code is:

static int prepare_packed_git_run_once = 0;
void prepare_packed_git(void)
{
    struct alternate_object_database *alt;

    if (prepare_packed_git_run_once)
        return;
    prepare_packed_git_one(get_object_directory(), 1);
    prepare_alt_odb();
    for (alt = alt_odb_list; alt; alt = alt->next)
        prepare_packed_git_one(alt->path, 0);
    rearrange_packed_git();
    prepare_packed_git_mru();
    prepare_packed_git_run_once = 1;
}

As we use the "prepare_packed_git_run_once" static, this function will
only be called only once when packed_git_mru has not yet been
initialized, so there will be no leak.

Check reprepare_packed_git(). It unsets the run_once flag, and then
calls prepare_packed_git() again.

-Peff