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From: Taylor Blau <me@ttaylorr.com>
To: git@vger.kernel.org
Cc: avarab@gmail.com, gitster@pobox.com
Subject: [PATCH v2 4/9] pack-write.c: rename `.idx` files after `*.rev`
Date: Thu, 9 Sep 2021 19:24:41 -0400	[thread overview]
Message-ID: <41d34b1f180350c466243ed5aa7f6a48a2ff2aeb.1631228928.git.me@ttaylorr.com> (raw)
In-Reply-To: <cover.1631228928.git.me@ttaylorr.com>

We treat the presence of an `.idx` file as the indicator of whether or
not it's safe to use a packfile. But `finish_tmp_packfile()` (which is
responsible for writing the pack and moving the temporary versions of
all of its auxiliary files into place) is inconsistent about the write
order.

Specifically, it moves the `.rev` file into place after the `.idx`,
leaving open the possibility to open a pack which looks "ready" (because
the `.idx` file exists and is readable) but appears momentarily to not
have a `.rev` file. This causes Git to fall back to generating the
pack's reverse index in memory.

Though racy, this amounts to an unnecessary slow-down at worst, and
doesn't affect the correctness of the resulting reverse index.

Close this race by moving the .rev file into place before moving the
.idx file into place.

This still leaves the issue of `.idx` files being renamed into place
before the auxiliary `.bitmap` file is renamed when in pack-object.c's
write_pack_file() "write_bitmap_index" is true. That race will be
addressed in subsequent commits.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
---
 pack-write.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pack-write.c b/pack-write.c
index 58bc5fbcdf..b9f9cd5c14 100644
--- a/pack-write.c
+++ b/pack-write.c
@@ -491,9 +491,9 @@ void finish_tmp_packfile(struct strbuf *name_buffer,
 				      pack_idx_opts->flags);
 
 	rename_tmp_packfile(name_buffer, pack_tmp_name, "pack");
-	rename_tmp_packfile(name_buffer, idx_tmp_name, "idx");
 	if (rev_tmp_name)
 		rename_tmp_packfile(name_buffer, rev_tmp_name, "rev");
+	rename_tmp_packfile(name_buffer, idx_tmp_name, "idx");
 
 	free((void *)idx_tmp_name);
 }
-- 
2.33.0.96.g73915697e6


  parent reply	other threads:[~2021-09-09 23:24 UTC|newest]

Thread overview: 81+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-01  2:05 [PATCH 0/2] pack-write,repack: prevent opening packs too early Taylor Blau
2021-09-01  2:06 ` [PATCH 1/2] pack-write.c: rename `.idx` file into place last Taylor Blau
2021-09-01  2:06 ` [PATCH 2/2] builtin/repack.c: move `.idx` files " Taylor Blau
2021-09-01  3:53 ` [PATCH 0/2] pack-write,repack: prevent opening packs too early Jeff King
2021-09-01  4:29   ` Taylor Blau
2021-09-01  4:59     ` Jeff King
2021-09-01  5:12       ` Taylor Blau
2021-09-01  6:08         ` Jeff King
2021-09-01 21:40           ` Taylor Blau
2021-09-07 16:07             ` Jeff King
2021-09-07 19:42 ` [PATCH 0/3] rename *.idx file into place last (also after *.bitmap) Ævar Arnfjörð Bjarmason
2021-09-07 19:42   ` [PATCH 1/3] pack-write: use more idiomatic strbuf usage for packname construction Ævar Arnfjörð Bjarmason
2021-09-07 22:21     ` Taylor Blau
2021-09-07 23:22       ` Ævar Arnfjörð Bjarmason
2021-09-07 19:42   ` [PATCH 2/3] pack-write: split up finish_tmp_packfile() function Ævar Arnfjörð Bjarmason
2021-09-07 22:28     ` Taylor Blau
2021-09-07 19:42   ` [PATCH 3/3] pack-write: rename *.idx file into place last (really!) Ævar Arnfjörð Bjarmason
2021-09-07 22:31     ` Taylor Blau
2021-09-07 22:36   ` [PATCH 0/3] rename *.idx file into place last (also after *.bitmap) Taylor Blau
2021-09-07 19:48 ` [PATCH 0/2] pack-write,repack: prevent opening packs too early Ævar Arnfjörð Bjarmason
2021-09-08  0:38 ` [PATCH v2 0/4] rename *.idx file into place last (also after *.bitmap) Ævar Arnfjörð Bjarmason
2021-09-08  0:38   ` [PATCH v2 1/4] pack.h: line-wrap the definition of finish_tmp_packfile() Ævar Arnfjörð Bjarmason
2021-09-08  0:38   ` [PATCH v2 2/4] pack-write: refactor renaming in finish_tmp_packfile() Ævar Arnfjörð Bjarmason
2021-09-08  4:22     ` Taylor Blau
2021-09-08  0:38   ` [PATCH v2 3/4] pack-write: split up finish_tmp_packfile() function Ævar Arnfjörð Bjarmason
2021-09-08  0:38   ` [PATCH v2 4/4] pack-write: rename *.idx file into place last (really!) Ævar Arnfjörð Bjarmason
2021-09-08  1:14     ` Ævar Arnfjörð Bjarmason
2021-09-08  9:18       ` Ævar Arnfjörð Bjarmason
2021-09-08  4:24     ` Taylor Blau
2021-09-08 22:17 ` [PATCH v2 0/3] prevent opening packs too early Taylor Blau
2021-09-08 22:17   ` [PATCH v2 1/3] pack-write.c: rename `.idx` files into place last Taylor Blau
2021-09-08 22:17   ` [PATCH v2 2/3] builtin/repack.c: move " Taylor Blau
2021-09-08 22:17   ` [PATCH v2 3/3] builtin/index-pack.c: " Taylor Blau
2021-09-08 23:52   ` [PATCH v2 0/3] prevent opening packs too early Ævar Arnfjörð Bjarmason
2021-09-09  0:50     ` Ævar Arnfjörð Bjarmason
2021-09-09  1:13       ` Taylor Blau
2021-09-09  1:33         ` Ævar Arnfjörð Bjarmason
2021-09-09  2:36           ` Ævar Arnfjörð Bjarmason
2021-09-09  2:49             ` Taylor Blau
2021-09-09  3:24 ` [PATCH 0/9] packfile: avoid .idx rename races Taylor Blau
2021-09-09  3:24   ` [PATCH 1/9] pack.h: line-wrap the definition of finish_tmp_packfile() Taylor Blau
2021-09-09  3:24   ` [PATCH 2/9] bulk-checkin.c: store checksum directly Taylor Blau
2021-09-09  7:38     ` Ævar Arnfjörð Bjarmason
2021-09-09  3:24   ` [PATCH 3/9] pack-write: refactor renaming in finish_tmp_packfile() Taylor Blau
2021-09-09 19:29     ` Junio C Hamano
2021-09-09 21:07       ` Taylor Blau
2021-09-09 23:30         ` Junio C Hamano
2021-09-09 23:31           ` Taylor Blau
2021-09-10  1:29         ` Junio C Hamano
2021-09-09  3:24   ` [PATCH 4/9] pack-write.c: rename `.idx` files after `*.rev` Taylor Blau
2021-09-09  7:46     ` Ævar Arnfjörð Bjarmason
2021-09-09 14:37       ` Taylor Blau
2021-09-09 19:32     ` Junio C Hamano
2021-09-09  3:25   ` [PATCH 5/9] builtin/repack.c: move `.idx` files into place last Taylor Blau
2021-09-09 19:38     ` Junio C Hamano
2021-09-09 21:08       ` Taylor Blau
2021-09-09  3:25   ` [PATCH 6/9] index-pack: refactor renaming in final() Taylor Blau
2021-09-09 19:45     ` Junio C Hamano
2021-09-09 21:11       ` Taylor Blau
2021-09-09  3:25   ` [PATCH 7/9] builtin/index-pack.c: move `.idx` files into place last Taylor Blau
2021-09-09  7:52     ` Ævar Arnfjörð Bjarmason
2021-09-09 19:45     ` Junio C Hamano
2021-09-09  3:25   ` [PATCH 8/9] pack-write: split up finish_tmp_packfile() function Taylor Blau
2021-09-09  3:25   ` [PATCH 9/9] pack-objects: rename .idx files into place after .bitmap files Taylor Blau
2021-09-09  7:54     ` Ævar Arnfjörð Bjarmason
2021-09-09 19:52       ` Junio C Hamano
2021-09-09 21:13         ` Taylor Blau
2021-09-09  8:06   ` [PATCH 0/9] packfile: avoid .idx rename races Ævar Arnfjörð Bjarmason
2021-09-09 14:40     ` Taylor Blau
2021-09-09 19:52       ` Junio C Hamano
2021-09-09 23:24   ` [PATCH v2 " Taylor Blau
2021-09-09 23:24     ` [PATCH v2 1/9] pack.h: line-wrap the definition of finish_tmp_packfile() Taylor Blau
2021-09-09 23:24     ` [PATCH v2 2/9] bulk-checkin.c: store checksum directly Taylor Blau
2021-09-09 23:24     ` [PATCH v2 3/9] pack-write: refactor renaming in finish_tmp_packfile() Taylor Blau
2021-09-09 23:24     ` Taylor Blau [this message]
2021-09-09 23:24     ` [PATCH v2 5/9] builtin/repack.c: move `.idx` files into place last Taylor Blau
2021-09-09 23:24     ` [PATCH v2 6/9] index-pack: refactor renaming in final() Taylor Blau
2021-09-09 23:24     ` [PATCH v2 7/9] builtin/index-pack.c: move `.idx` files into place last Taylor Blau
2021-09-09 23:24     ` [PATCH v2 8/9] pack-write: split up finish_tmp_packfile() function Taylor Blau
2021-09-09 23:25     ` [PATCH v2 9/9] pack-objects: rename .idx files into place after .bitmap files Taylor Blau
2021-09-10  1:35     ` [PATCH v2 0/9] packfile: avoid .idx rename races Junio C Hamano

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