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refs: fix recursing get_main_ref_store() with "onbranch" config

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When we have an "onbranch" condition we need to ask the reference
database whether HEAD currently points at the configured branch. This
unfortunately creates a chicken-and-egg problem:

  - The reference database needs to read the configuration so that it
    can configure itself.

  - The configuration needs to construct a reference database to fully
    parse all of its conditionals.

The way we handle this is by simply excluding "onbranch" conditionals
when we haven't yet configured the reference database.

The mechanism for this is broken though: to verify whether or not we
have configured the reference database we check whether its format is
set to `REF_STORAGE_UNKNOWN` in `include_by_branch()`. But typically,
the format _is_ already known at that time because we set it up during
repository discovery in "setup.c".

The consequence is that we have recursion:

  1. We call `get_main_ref_store()`.

  2. We don't yet have a reference store, so we call `ref_store_init()`.

  3. We parse the configuration required for the reference store.

  4. We eventually end up in `include_by_branch()`.

  5. We have already configured the reference storage format, so we end
     up calling `get_main_ref_store()` again.

We still haven't finished (1) though, so `get_main_ref_store()` will now
call `ref_store_init()` a second time. The end result is that we have
constructed the same reference store twice.

Of course, as both reference stores would be assigned to `refs_private`,
we leak one of those two instances. This never surfaced as an actual
leak though because the pointer is kept alive by the "chdir_notify"
subsystem.

For now, we can fix the issue by explicitly unsetting the reference
storage format before constructing it. This makes the mentioned check
trigger as expected, and consequently we won't end up constructing a
second reference database at all. Ultimately, this means that we
consistently stop evaluating "onbranch" conditions when constructing the
main reference database.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Patrick Steinhardt
2026-06-10 16:57:13 +02:00
committed by Junio C Hamano
parent 3f6819c895
commit 238191ecfc
1 changed files with 18 additions and 2 deletions
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20
refs.c
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@@ -2351,15 +2351,31 @@ void ref_store_release(struct ref_store *ref_store)
struct ref_store *get_main_ref_store(struct repository *r)
{
enum ref_storage_format format;
if (r->refs_private)
return r->refs_private;
if (!r->gitdir)
BUG("attempting to get main_ref_store outside of repository");
r->refs_private = ref_store_init(r, r->ref_storage_format,
r->gitdir, REF_STORE_ALL_CAPS);
/*
* When constructing the reference backend we'll end up reading the Git
* configuration. This means we'll also try to evaluate "onbranch"
* conditions.
*
* We cannot read branches when constructing the refdb, so it is not
* possible to evaluate those conditions in the first place. To gate
* their evaluation we check whether or not the reference storage
* format has been configured -- we thus have to temporarily set it to
* UNKNOWN here so that we don't end up recursing.
*/
format = r->ref_storage_format;
r->ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
r->refs_private = ref_store_init(r, format, r->gitdir, REF_STORE_ALL_CAPS);
r->refs_private = maybe_debug_wrap_ref_store(r->gitdir, r->refs_private);
r->ref_storage_format = format;
return r->refs_private;
}