grep: fix race conditions on userdiff calls

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> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Matheus Tavares committed Jan 15, 2020 at 23:39 UTC c3a5bb31c1567edd1671b54726d4acbb10563a2c

1 file changed +6 -1

grep.c

+6 -1

@@ -1816,7 +1816,9 @@ static int grep_source_1(struct grep_opt *opt, struct grep_source *gs, int colle

1816 * is not thread-safe.

1817 */

1818 grep_attr_lock();

1819 + grep_read_lock();

1820 textconv = userdiff_get_textconv(opt->repo, gs->driver);

1821 + grep_read_unlock();

1822 grep_attr_unlock();

1823 }

1824

@@ -2184,8 +2186,11 @@ void grep_source_load_driver(struct grep_source *gs,

2186 return;

2187

2188 grep_attr_lock();

2187 - if (gs->path)

2189 + if (gs->path) {

2190 + grep_read_lock();

2191 gs->driver = userdiff_find_by_path(istate, gs->path);

2192 + grep_read_unlock();

2193 + }

2194 if (!gs->driver)

2195 gs->driver = userdiff_find_by_name("default");

2196 grep_attr_unlock();