grep: take the read-lock when adding a submodule

With --recurse-submodules, we add each submodule that we encounter to the list of alternate object databases. With threading, our changes to the list are not protected against races. Indeed, ThreadSanitizer reports a race when we call `add_to_alternates_memory()` around the same time that another thread is reading in the list through `read_sha1_file()`. Take the grep read-lock while adding the submodule. The lock is used to serialize uses of non-thread-safe parts of Git's API, including `read_sha1_file()`. Helped-by: Brandon Williams <[email protected]> Signed-off-by: Martin Ågren <[email protected]> Acked-by: Brandon Williams <[email protected]> Reviewed-by: Jeff King <[email protected]> Signed-off-by: Junio C Hamano <[email protected]>
dyrone · Nov 2, 2017 · 9560e62 · 9560e62
1 parent f9ee2fc
commit 9560e62
Showing 1 changed file with 2 additions and 0 deletions.
diff --git a/builtin/grep.c b/builtin/grep.c
@@ -431,7 +431,9 @@ static int grep_submodule(struct grep_opt *opt, struct repository *superproject,
 	 * store is no longer global and instead is a member of the repository
 	 * object.
 	 */
+	grep_read_lock();
 	add_to_alternates_memory(submodule.objectdir);
+	grep_read_unlock();
 
 	if (oid) {
 		struct object *object;