grep: Fix race condition in delta_base_cache

When running large git grep (ie: git grep regexp $(git rev-list --all)), glibc error sometimes occur:
*** glibc detected *** git: double free or corruption (!prev): 0x00000000010abdf0 ***

According to gdb the problem originate from release_delta_cash (sha1_file.c:1703)
		free(ent->data);

>From my analysis it seems that git grep threads do acquire lock before calling read_sha1_file but not before calling
read_object_with_reference who ends up calling read_sha1_file too.

Adding the lock around read_object_with_reference seems to fix the issue for me.
I've ran git grep about a dozen time and seen no more error while
it usually happened half the time before.

Signed-off-by: Nicolas Morey-Chaisemartin <nicolas@morey-chaisemartin.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin-grep.c b/builtin-grep.c
index 6cc743d7c585fa443f18a700455a4da662dec49f..0eb192d488e64b693184b7d00f7740cbe075c879 100644 (file)
--- a/builtin-grep.c
+++ b/builtin-grep.c
@@ -632,8 +632,12 @@ static int grep_object(struct grep_opt *opt, const char **paths,
                void *data;
                unsigned long size;
                int hit;
+
+               read_sha1_lock();
                data = read_object_with_reference(obj->sha1, tree_type,
                                                  &size, NULL);
+               read_sha1_unlock();
+
                if (!data)
                        die("unable to read tree (%s)", sha1_to_hex(obj->sha1));
                init_tree_desc(&tree, data, size);