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grep: protect packed_git [re-]initialization

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Some fields in struct raw_object_store are lazy initialized by the
thread-unsafe packfile.c:prepare_packed_git(). Although this function is
present in the call stack of git-grep threads, all paths to it are
currently protected by obj_read_lock() (and the main thread usually
indirectly calls it before firing the worker threads, anyway). However,
it's possible that future modifications add new unprotected paths to it,
introducing a race condition. Because errors derived from it wouldn't
happen often, it could be hard to detect. So to prevent future
headaches, let's force eager initialization of packed_git when setting
git-grep up. There'll be a small overhead in the cases where we didn't
really need to prepare packed_git during execution but this shouldn't be
very noticeable.

Also, packed_git may be re-initialized by
packfile.c:reprepare_packed_git(). Again, all paths to it in git-grep
are already protected by obj_read_lock() but it may suffer from the same
problem in the future. So let's also internally protect it with
obj_read_lock() (which is a recursive mutex).

Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Matheus Tavares 2020-01-15 23:39:57 -03:00 committed by Junio C Hamano
parent c441ea4edc
commit 6c307626f1
2 changed files with 8 additions and 2 deletions
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8
builtin/grep.c
View File

@ -24,6 +24,7 @@
#include "submodule.h"
#include "submodule-config.h"
#include "object-store.h"
#include "packfile.h"
static char const * const grep_usage[] = {
N_("git grep [<options>] [-e] <pattern> [<rev>...] [[--] <path>...]"),
@ -1074,11 +1075,14 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
skip_first_line = 1;
/*
* Pre-read gitmodules (if not read already) to prevent racy
* lazy reading in worker threads.
* Pre-read gitmodules (if not read already) and force eager
* initialization of packed_git to prevent racy lazy
* reading/initialization once worker threads are started.
*/
if (recurse_submodules)
repo_read_gitmodules(the_repository, 1);
if (startup_info->have_repository)
(void)get_packed_git(the_repository);
start_threads(&opt);
} else {

2
packfile.c
View File

@ -1004,12 +1004,14 @@ void reprepare_packed_git(struct repository *r)
{
struct object_directory *odb;
obj_read_lock();
for (odb = r->objects->odb; odb; odb = odb->next)
odb_clear_loose_cache(odb);
r->objects->approximate_object_count_valid = 0;
r->objects->packed_git_initialized = 0;
prepare_packed_git(r);
obj_read_unlock();
}
struct packed_git *get_packed_git(struct repository *r)