[PATCH v5 08/13] refs/files: add a comment about refs_reflog_exists() call
- From
Ævar Arnfjörð Bjarmason <avarab@gmail.com>
- Date
- Aug 23, 2021, 11:36 UTC
- Message-ID
- <patch-v5-08.13-51abe459e70-20210823T113115Z-avarab@gmail.com>
- In-Reply-To
- <cover-v5-00.13-00000000000-20210823T113115Z-avarab@gmail.com>
Add a comment about why it is that we need to check for the the existence of a reflog we're deleting after we've successfully acquired the lock in files_reflog_expire(). As noted in [1] the lock protocol for reflogs is somewhat intuitive.
This early exit code the comment applies to dates all the way back to 4264dc15e19 (git reflog expire, 2006-12-19).
1. https://lore.kernel.org/git/54DCDA42.2060800@alum.mit.edu/
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> --- refs/files-backend.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/refs/files-backend.c b/refs/files-backend.c index 997e021c1c4..fbcd0c790bc 100644 --- a/refs/files-backend.c +++ b/refs/files-backend.c @@ -3061,6 +3061,19 @@ static int files_reflog_expire(struct ref_store *ref_store, strbuf_release(&err); return -1; } + + /* + * When refs are deleted, their reflog is deleted before the + * ref itself is deleted. This is because there is no separate + * lock for reflog; instead we take a lock on the ref with + * lock_ref_oid_basic(). + * + * If a race happens and the reflog doesn't exist after we've + * acquired the lock that's OK. We've got nothing more to do; + * We were asked to delete the reflog, but someone else + * deleted it! The caller doesn't care that we deleted it, + * just that it is deleted. So we can return successfully. + */ if (!refs_reflog_exists(ref_store, refname)) { unlock_ref(lock); return 0;
-- 2.33.0.662.g438caf9576d