stop leaking lock structs in some simple cases

Now that it's safe to declare a "struct lock_file" on the
stack, we can do so (and avoid an intentional leak). These
leaks were found by running t0000 and t0001 under valgrind
(though certainly other similar leaks exist and just don't
happen to be exercised by those tests).

Initializing the lock_file's inner tempfile with NULL is not
strictly necessary in these cases, but it's a good practice
to model.  It means that if we were to call a function like
rollback_lock_file() on a lock that was never taken in the
first place, it becomes a quiet noop (rather than undefined
behavior).

Likewise, it's always safe to rollback_lock_file() on a file
that has already been committed or deleted, since that
operation is a noop on an inactive lockfile (and that's why
the case in config.c can drop the "if (lock)" check as we
move away from using a pointer).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 7 insertions, 17 deletions

diff --git a/config.c b/config.c
index d0d8ce823a..7931182a54 100644
--- a/config.c
+++ b/config.c
@@ -2450,7 +2450,7 @@ int git_config_set_multivar_in_file_gently(const char *config_filename,
 {
 	int fd = -1, in_fd = -1;
 	int ret;
-	struct lock_file *lock = NULL;
+	struct lock_file lock = LOCK_INIT;
 	char *filename_buf = NULL;
 	char *contents = NULL;
 	size_t contents_sz;
@@ -2469,8 +2469,7 @@ int git_config_set_multivar_in_file_gently(const char *config_filename,
 	 * The lock serves a purpose in addition to locking: the new
 	 * contents of .git/config will be written into it.
 	 */
-	lock = xcalloc(1, sizeof(struct lock_file));
-	fd = hold_lock_file_for_update(lock, config_filename, 0);
+	fd = hold_lock_file_for_update(&lock, config_filename, 0);
 	if (fd < 0) {
 		error_errno("could not lock config file %s", config_filename);
 		free(store.key);
@@ -2583,8 +2582,8 @@ int git_config_set_multivar_in_file_gently(const char *config_filename,
 		close(in_fd);
 		in_fd = -1;
 
-		if (chmod(get_lock_file_path(lock), st.st_mode & 07777) < 0) {
-			error_errno("chmod on %s failed", get_lock_file_path(lock));
+		if (chmod(get_lock_file_path(&lock), st.st_mode & 07777) < 0) {
+			error_errno("chmod on %s failed", get_lock_file_path(&lock));
 			ret = CONFIG_NO_WRITE;
 			goto out_free;
 		}
@@ -2639,28 +2638,19 @@ int git_config_set_multivar_in_file_gently(const char *config_filename,
 		contents = NULL;
 	}
 
-	if (commit_lock_file(lock) < 0) {
+	if (commit_lock_file(&lock) < 0) {
 		error_errno("could not write config file %s", config_filename);
 		ret = CONFIG_NO_WRITE;
-		lock = NULL;
 		goto out_free;
 	}
 
-	/*
-	 * lock is committed, so don't try to roll it back below.
-	 * NOTE: Since lockfile.c keeps a linked list of all created
-	 * lock_file structures, it isn't safe to free(lock).  It's
-	 * better to just leave it hanging around.
-	 */
-	lock = NULL;
 	ret = 0;
 
 	/* Invalidate the config cache */
 	git_config_clear();
 
 out_free:
-	if (lock)
-		rollback_lock_file(lock);
+	rollback_lock_file(&lock);
 	free(filename_buf);
 	if (contents)
 		munmap(contents, contents_sz);
@@ -2669,7 +2659,7 @@ out_free:
 	return ret;
 
 write_err_out:
-	ret = write_error(get_lock_file_path(lock));
+	ret = write_error(get_lock_file_path(&lock));
 	goto out_free;
 
 }