config: move flockfile() closer to unlocked functions

Commit 260d408 (config: use getc_unlocked when reading
from file, 2015-04-16) taught git_config_from_file() to lock
the filehandle so that we could safely use the faster
unlocked functions to access the handle.

However, it split the logic into two places:

  1. The master lock/unlock happens in git_config_from_file().

  2. The decision to use the unlocked functions happens in
     do_config_from_file().

That means that if anybody calls the latter function, they
will accidentally use the unlocked functions without holding
the lock. And indeed, git_config_from_stdin() does so.

In practice, this hasn't been a problem since this code
isn't generally multi-threaded (and even if some Git program
happened to have another thread running, it's unlikely to be
reading from stdin). But it's a good practice to make sure
we're always holding the lock before using the unlocked
functions.

Helped-by: Johannes Schindelin <[email protected]>
Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

config.c

@@ -1408,6 +1408,7 @@ static int do_config_from_file(config_fn_t fn,
 		void *data)
 {
 	struct config_source top;
+	int ret;
 
 	top.u.file = f;
 	top.origin_type = origin_type;
@@ -1418,7 +1419,10 @@ static int do_config_from_file(config_fn_t fn,
 	top.do_ungetc = config_file_ungetc;
 	top.do_ftell = config_file_ftell;
 
-	return do_config_from(&top, fn, data);
+	flockfile(f);
+	ret = do_config_from(&top, fn, data);
+	funlockfile(f);
+	return ret;
 }
 
 static int git_config_from_stdin(config_fn_t fn, void *data)
@@ -1433,9 +1437,7 @@ int git_config_from_file(config_fn_t fn, const char *filename, void *data)
 
 	f = fopen_or_warn(filename, "r");
 	if (f) {
-		flockfile(f);
 		ret = do_config_from_file(fn, CONFIG_ORIGIN_FILE, filename, filename, f, data);
-		funlockfile(f);
 		fclose(f);
 	}
 	return ret;