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[PATCH v2 01/11] grep: fix race conditions on userdiff calls

From
Matheus Tavares <matheus.bernardino@usp.br>
Date
Sep 30, 2019, 01:50 UTC
Message-ID
<0f31cb0c126e824008d35d5cba52dd1c3c115c00.1569808052.git.matheus.bernardino@usp.br>
In-Reply-To
<cover.1569808052.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 bellow:

- 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 cd952ef5d3..b29946def2 100644
--- a/grep.c
+++ b/grep.c
@@ -1809,7 +1809,9 @@ 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();
 	}
 
@@ -2177,8 +2179,11 @@ 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();

-- 
2.23.0
Previous: Matheus TavaresNext: Matheus Tavares
Message 7 of 47 in “grep: re-enable threads when cached, w/ parallel inflation”
  1. Matheus TavaresAug 10, 2019
  2. [GSoC][PATCH 1/4] object-store: add lock to read_object_file_extended()Matheus Tavares, Aug 10, 2019
  3. [GSoC][PATCH 2/4] grep: allow locks to be enabled individuallyMatheus Tavares, Aug 10, 2019
  4. [GSoC][PATCH 3/4] grep: disable grep_read_mutex when possibleMatheus Tavares, Aug 10, 2019
  5. [GSoC][PATCH 4/4] grep: re-enable threads in some non-worktree casesMatheus Tavares, Aug 10, 2019
  6. 00/11 grep: improve threading and fix race conditionsMatheus Tavares, Sep 30, 2019
  7. 01/11 grep: fix race conditions on userdiff callsMatheus Tavares, Sep 30, 2019
  8. 02/11 grep: fix race conditions at grep_submodule()Matheus Tavares, Sep 30, 2019
  9. 03/11 grep: fix racy calls in grep_objects()Matheus Tavares, Sep 30, 2019
  10. 04/11 replace-object: make replace operations thread-safeMatheus Tavares, Sep 30, 2019
  11. 05/11 object-store: allow threaded access to object readingMatheus Tavares, Sep 30, 2019
  12. Jonathan TanNov 12, 2019
  13. Jeff KingNov 13, 2019
  14. Matheus Tavares BernardinoNov 14, 2019
  15. Jeff KingNov 14, 2019
  16. Jonathan TanNov 14, 2019
  17. Jeff KingNov 15, 2019
  18. Matheus Tavares BernardinoDec 19, 2019
  19. Matheus Tavares BernardinoJan 9, 2020
  20. Christian CouderJan 10, 2020
  21. 06/11 grep: replace grep_read_mutex by internal obj read lockMatheus Tavares, Sep 30, 2019
  22. squash! grep: replace grep_read_mutex by internal obj read lockMatheus Tavares, Oct 1, 2019
  23. 07/11 submodule-config: add skip_if_read option to repo_read_gitmodules()Matheus Tavares, Sep 30, 2019
  24. 08/11 grep: allow submodule functions to run in parallelMatheus Tavares, Sep 30, 2019
  25. 09/11 grep: protect packed_git [re-]initializationMatheus Tavares, Sep 30, 2019
  26. 10/11 grep: re-enable threads in non-worktree caseMatheus Tavares, Sep 30, 2019
  27. 11/11 grep: move driver pre-load out of critical sectionMatheus Tavares, Sep 30, 2019
  28. 00/12 grep: improve threading and fix race conditionsMatheus Tavares, Jan 16, 2020
  29. 01/12 grep: fix race conditions on userdiff callsMatheus Tavares, Jan 16, 2020
  30. 02/12 grep: fix race conditions at grep_submodule()Matheus Tavares, Jan 16, 2020
  31. 03/12 grep: fix racy calls in grep_objects()Matheus Tavares, Jan 16, 2020
  32. 04/12 replace-object: make replace operations thread-safeMatheus Tavares, Jan 16, 2020
  33. 05/12 object-store: allow threaded access to object readingMatheus Tavares, Jan 16, 2020
  34. 06/12 grep: replace grep_read_mutex by internal obj read lockMatheus Tavares, Jan 16, 2020
  35. 07/12 submodule-config: add skip_if_read option to repo_read_gitmodules()Matheus Tavares, Jan 16, 2020
  36. 08/12 grep: allow submodule functions to run in parallelMatheus Tavares, Jan 16, 2020
  37. SZEDER GáborJan 29, 2020
  38. Junio C HamanoJan 29, 2020
  39. Junio C HamanoJan 29, 2020
  40. Matheus Tavares BernardinoJan 29, 2020
  41. Philippe BlainJan 30, 2020
  42. 09/12 grep: protect packed_git [re-]initializationMatheus Tavares, Jan 16, 2020
  43. 10/12 grep: re-enable threads in non-worktree caseMatheus Tavares, Jan 16, 2020
  44. 11/12 grep: move driver pre-load out of critical sectionMatheus Tavares, Jan 16, 2020
  45. 12/12 grep: use no. of cores as the default no. of threadsMatheus Tavares, Jan 16, 2020
  46. Victor LeschukJan 16, 2020
  47. Matheus TavaresJan 16, 2020

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