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From: Jeff King <peff@peff.net>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: "Junio C Hamano" <gitster@pobox.com>,
	"Git List" <git@vger.kernel.org>,
	"Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>,
	"Michael Haggerty" <mhagger@alum.mit.edu>,
	"Stefan Beller" <stefanbeller@gmail.com>,
	"Jonathan Nieder" <jrnieder@gmail.com>
Subject: Re: BUG: Race condition due to reflog expiry in "gc"
Date: Wed, 13 Mar 2019 20:25:00 -0400	[thread overview]
Message-ID: <20190314002459.GE31968@sigill.intra.peff.net> (raw)
In-Reply-To: <87imwmbv7l.fsf@evledraar.gmail.com>

On Wed, Mar 13, 2019 at 05:22:22PM +0100, Ævar Arnfjörð Bjarmason wrote:

> > That's what the retry-with-timeout is supposed to address, so maybe it
> > works. But I wouldn't be surprised if it's insufficient in practice,
> > since the reflog code may walk big parts of the graph under lock,
> > checking reachability.
> 
> I suppose this can happen if the reflog for a given branch is so big
> that it takes us more than 100ms to parse it, but e.g. O(n) refs
> shouldn't matter, since we only hold the lock on one ref at a time.

I think it's more than parsing, though.

It's been a while since I've dug into the reflog expiration code, but my
recollection is that it can actually walk parts of the graph (looking
for what's reachable) while processing the reflog. That can be tens of
seconds in decent-sized repositories.

-Peff

      parent reply	other threads:[~2019-03-14  0:26 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-12 23:28 BUG: Race condition due to reflog expiry in "gc" Ævar Arnfjörð Bjarmason
2019-03-13  1:43 ` Junio C Hamano
2019-03-13 10:28   ` Ævar Arnfjörð Bjarmason
2019-03-13 16:02     ` Jeff King
2019-03-13 16:22       ` Ævar Arnfjörð Bjarmason
2019-03-13 23:54         ` [PATCH 0/5] gc: minor code cleanup + contention fixes Ævar Arnfjörð Bjarmason
2019-03-14 12:34           ` [PATCH v2 0/7] " Ævar Arnfjörð Bjarmason
2019-03-15 15:59             ` [PATCH v3 0/8] " Ævar Arnfjörð Bjarmason
2019-03-18  6:13               ` Junio C Hamano
2019-03-28 16:14               ` [PATCH v4 0/7] gc: tests and handle reflog expire config Ævar Arnfjörð Bjarmason
2019-03-28 16:14               ` [PATCH v4 1/7] gc: remove redundant check for gc_auto_threshold Ævar Arnfjörð Bjarmason
2019-03-28 16:14               ` [PATCH v4 2/7] gc: convert to using the_hash_algo Ævar Arnfjörð Bjarmason
2019-03-28 16:14               ` [PATCH v4 3/7] gc: refactor a "call me once" pattern Ævar Arnfjörð Bjarmason
2019-03-28 16:14               ` [PATCH v4 4/7] reflog tests: make use of "test_config" idiom Ævar Arnfjörð Bjarmason
2019-03-28 16:14               ` [PATCH v4 5/7] reflog tests: test for the "points nowhere" warning Ævar Arnfjörð Bjarmason
2019-03-28 16:14               ` [PATCH v4 6/7] reflog tests: assert lack of early exit with expiry="never" Ævar Arnfjörð Bjarmason
2019-03-28 16:14               ` [PATCH v4 7/7] gc: handle & check gc.reflogExpire config Ævar Arnfjörð Bjarmason
2019-03-15 15:59             ` [PATCH v3 1/8] gc: remove redundant check for gc_auto_threshold Ævar Arnfjörð Bjarmason
2019-03-15 15:59             ` [PATCH v3 2/8] gc: convert to using the_hash_algo Ævar Arnfjörð Bjarmason
2019-03-15 15:59             ` [PATCH v3 3/8] gc: refactor a "call me once" pattern Ævar Arnfjörð Bjarmason
2019-03-15 15:59             ` [PATCH v3 4/8] reflog tests: make use of "test_config" idiom Ævar Arnfjörð Bjarmason
2019-03-15 15:59             ` [PATCH v3 5/8] reflog tests: test for the "points nowhere" warning Ævar Arnfjörð Bjarmason
2019-03-15 15:59             ` [PATCH v3 6/8] reflog tests: assert lack of early exit with expiry="never" Ævar Arnfjörð Bjarmason
2019-03-19  6:20               ` Jeff King
2019-03-15 15:59             ` [PATCH v3 7/8] gc: handle & check gc.reflogExpire config Ævar Arnfjörð Bjarmason
2019-03-15 15:59             ` [PATCH v3 8/8] reflog expire: don't assert the OID when locking refs Ævar Arnfjörð Bjarmason
     [not found]               ` <b870a17d-2103-41b8-3cbc-7389d5fff33a@alum.mit.edu>
2019-03-21 14:10                 ` Ævar Arnfjörð Bjarmason
2019-03-19  6:27             ` [PATCH v2 0/7] gc: minor code cleanup + contention fixes Jeff King
2019-03-14 12:34           ` [PATCH v2 1/7] gc: remove redundant check for gc_auto_threshold Ævar Arnfjörð Bjarmason
2019-03-14 12:34           ` [PATCH v2 2/7] gc: convert to using the_hash_algo Ævar Arnfjörð Bjarmason
2019-03-15  9:51             ` Duy Nguyen
2019-03-15 10:42               ` Ævar Arnfjörð Bjarmason
2019-03-15 15:49                 ` Johannes Schindelin
2019-03-14 12:34           ` [PATCH v2 3/7] gc: refactor a "call me once" pattern Ævar Arnfjörð Bjarmason
2019-03-14 12:34           ` [PATCH v2 4/7] reflog tests: make use of "test_config" idiom Ævar Arnfjörð Bjarmason
2019-03-14 12:34           ` [PATCH v2 5/7] reflog: exit early if there's no work to do Ævar Arnfjörð Bjarmason
2019-03-15 10:01             ` Duy Nguyen
2019-03-15 15:51               ` Ævar Arnfjörð Bjarmason
2019-03-14 12:34           ` [PATCH v2 6/7] gc: don't run "reflog expire" when keeping reflogs Ævar Arnfjörð Bjarmason
2019-03-15 10:05             ` Duy Nguyen
2019-03-15 10:24               ` Ævar Arnfjörð Bjarmason
2019-03-15 10:32                 ` Duy Nguyen
2019-03-15 15:51                 ` Johannes Schindelin
2019-03-18  6:04                 ` Junio C Hamano
2019-03-14 12:34           ` [PATCH v2 7/7] reflog expire: don't assert the OID when locking refs Ævar Arnfjörð Bjarmason
2019-03-15 11:10             ` Duy Nguyen
2019-03-15 15:52               ` Ævar Arnfjörð Bjarmason
2019-03-13 23:54         ` [PATCH 1/5] gc: remove redundant check for gc_auto_threshold Ævar Arnfjörð Bjarmason
2019-03-14  0:25           ` Jeff King
2019-03-13 23:54         ` [PATCH 2/5] gc: convert to using the_hash_algo Ævar Arnfjörð Bjarmason
2019-03-14  0:26           ` Jeff King
2019-03-13 23:54         ` [PATCH 3/5] gc: refactor a "call me once" pattern Ævar Arnfjörð Bjarmason
2019-03-14  0:30           ` Jeff King
2019-03-13 23:54         ` [PATCH 4/5] gc: don't run "reflog expire" when keeping reflogs Ævar Arnfjörð Bjarmason
2019-03-14  0:40           ` Jeff King
2019-03-14  4:51             ` Junio C Hamano
2019-03-14 19:26               ` Jeff King
2019-03-13 23:54         ` [PATCH 5/5] reflog expire: don't assert the OID when locking refs Ævar Arnfjörð Bjarmason
2019-03-14  0:44           ` Jeff King
2019-03-14  0:25         ` Jeff King [this message]

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