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From: Matheus Tavares <matheus.bernardino@usp.br>
To: git@vger.kernel.org
Cc: christian.couder@gmail.com, gitster@pobox.com,
	jrnieder@gmail.com, olyatelezhnaya@gmail.com, pclouds@gmail.com,
	jonathantanmy@google.com, peff@peff.net,
	Ramkumar Ramachandra <artagnon@gmail.com>,
	Eric Wong <e@80x24.org>
Subject: [PATCH v3 01/12] grep: fix race conditions on userdiff calls
Date: Wed, 15 Jan 2020 23:39:49 -0300
Message-ID: <e2f3d377f5408d3d9365b8ac1b785d6d3f0437a9.1579141989.git.matheus.bernardino@usp.br> (raw)
In-Reply-To: <cover.1579141989.git.matheus.bernardino@usp.br>

git-grep uses an internal grep_read_mutex to protect object reading
operations. Similarly, there's a grep_attr_mutex to protect calls to the
gitattributes machinery. However, two of the three functions protected
by the last mutex may also perform object reading, as seen below:

- userdiff_get_textconv() > notes_cache_init() >
  notes_cache_match_validity() > lookup_commit_reference_gently() >
  parse_object() > repo_has_object_file() >
  repo_has_object_file_with_flags() > oid_object_info_extended()

- userdiff_find_by_path() > git_check_attr() > collect_some_attrs() >
  prepare_attr_stack() > read_attr() > read_attr_from_index() >
  read_blob_data_from_index() > read_object_file()

As these calls are not protected by grep_read_mutex, there might be race
conditions with other threads performing object reading (e.g. threads
calling fill_textconv() at grep.c:fill_textconv_grep()). To prevent
that, let's make sure to acquire the lock before both of these calls.

Note: this patch might slow down the threaded grep in worktree, for the
sake of thread-safeness. However, in the following patches, we should
regain performance by replacing grep_read_mutex for an internal object
reading lock and allowing parallel inflation during object reading.

Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br>
---
 grep.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/grep.c b/grep.c
index 0552b127c1..c028f70aba 100644
--- a/grep.c
+++ b/grep.c
@@ -1816,7 +1816,9 @@ static int grep_source_1(struct grep_opt *opt, struct grep_source *gs, int colle
 		 * is not thread-safe.
 		 */
 		grep_attr_lock();
+		grep_read_lock();
 		textconv = userdiff_get_textconv(opt->repo, gs->driver);
+		grep_read_unlock();
 		grep_attr_unlock();
 	}
 
@@ -2184,8 +2186,11 @@ void grep_source_load_driver(struct grep_source *gs,
 		return;
 
 	grep_attr_lock();
-	if (gs->path)
+	if (gs->path) {
+		grep_read_lock();
 		gs->driver = userdiff_find_by_path(istate, gs->path);
+		grep_read_unlock();
+	}
 	if (!gs->driver)
 		gs->driver = userdiff_find_by_name("default");
 	grep_attr_unlock();
-- 
2.24.1


  reply index

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-10 20:27 [GSoC][PATCH 0/4] grep: re-enable threads when cached, w/ parallel inflation Matheus Tavares
2019-09-30  1:50 ` [PATCH v2 00/11] grep: improve threading and fix race conditions Matheus Tavares
2020-01-16  2:39   ` [PATCH v3 00/12] " Matheus Tavares
2020-01-16  2:39     ` Matheus Tavares [this message]
2020-01-16  2:39     ` [PATCH v3 02/12] grep: fix race conditions at grep_submodule() Matheus Tavares
2020-01-16  2:39     ` [PATCH v3 03/12] grep: fix racy calls in grep_objects() Matheus Tavares
2020-01-16  2:39     ` [PATCH v3 04/12] replace-object: make replace operations thread-safe Matheus Tavares
2020-01-16  2:39     ` [PATCH v3 05/12] object-store: allow threaded access to object reading Matheus Tavares
2020-01-16  2:39     ` [PATCH v3 06/12] grep: replace grep_read_mutex by internal obj read lock Matheus Tavares
2020-01-16  2:39     ` [PATCH v3 07/12] submodule-config: add skip_if_read option to repo_read_gitmodules() Matheus Tavares
2020-01-16  2:39     ` [PATCH v3 08/12] grep: allow submodule functions to run in parallel Matheus Tavares
2020-01-29 11:26       ` SZEDER Gábor
2020-01-29 18:49         ` Junio C Hamano
2020-01-29 18:57         ` Junio C Hamano
2020-01-29 20:42           ` Matheus Tavares Bernardino
2020-01-30 13:28             ` Philippe Blain
2020-01-16  2:39     ` [PATCH v3 09/12] grep: protect packed_git [re-]initialization Matheus Tavares
2020-01-16  2:39     ` [PATCH v3 10/12] grep: re-enable threads in non-worktree case Matheus Tavares
2020-01-16  2:39     ` [PATCH v3 11/12] grep: move driver pre-load out of critical section Matheus Tavares
2020-01-16  2:40     ` [PATCH v3 12/12] grep: use no. of cores as the default no. of threads Matheus Tavares
2020-01-16 13:11       ` Victor Leschuk
2020-01-16 14:47         ` [PATCH] " Matheus Tavares

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