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[2a01:4f8:120:2468::2]) by smtp.gmail.com with ESMTPSA id n18sm1214545wrt.89.2021.07.26.16.44.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 Jul 2021 16:44:35 -0700 (PDT) From: =?UTF-8?q?=C3=86var=20Arnfj=C3=B6r=C3=B0=20Bjarmason?= To: git@vger.kernel.org Cc: Junio C Hamano , Jeff King , Han-Wen Nienhuys , Michael Haggerty , =?UTF-8?q?=C3=86var=20Arnfj=C3=B6r=C3=B0=20Bjarmason?= Subject: [PATCH v4 07/11] refs/files: add a comment about refs_reflog_exists() call Date: Tue, 27 Jul 2021 01:44:23 +0200 Message-Id: X-Mailer: git-send-email 2.32.0.988.g1a6a4b2c5f In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org 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 --- refs/files-backend.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/refs/files-backend.c b/refs/files-backend.c index af332fa8fe..5415306416 100644 --- a/refs/files-backend.c +++ b/refs/files-backend.c @@ -3068,6 +3068,19 @@ 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; -- 2.32.0.956.g6b0c84ceda8