fs: sync: Avoid calling fdget without fdput

When adding fsync support, we check for fsync_enabled() in several
cases but it appears that we should fdput() after fdget() but the
current code just check for fsync_enabled and directly return in
some cases after calling fdget().

Fix it by checking fsync_enabled first and move the f initialization
after the check. Also remove some unnecessary fsync_enabled checks as
this will be checked later in do_fsync().

Signed-off-by: Wang Han <416810799@qq.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>

fs/sync.c

@@ -152,7 +152,7 @@ void emergency_sync(void)
  */
 SYSCALL_DEFINE1(syncfs, int, fd)
 {
-	struct fd f = fdget(fd);
+	struct fd f;
 	struct super_block *sb;
 	int ret;
 
@@ -211,21 +211,19 @@ EXPORT_SYMBOL(vfs_fsync_range);
  */
 int vfs_fsync(struct file *file, int datasync)
 {
-	if (!fsync_enabled)
-		return 0;
-
 	return vfs_fsync_range(file, 0, LLONG_MAX, datasync);
 }
 EXPORT_SYMBOL(vfs_fsync);
 
 static int do_fsync(unsigned int fd, int datasync)
 {
-	struct fd f = fdget(fd);
+	struct fd f;
 	int ret = -EBADF;
 
 	if (!fsync_enabled)
 		return 0;
 
+	f = fdget(fd);
 	if (f.file) {
 		ret = vfs_fsync(f.file, datasync);
 		fdput(f);
@@ -236,17 +234,11 @@ static int do_fsync(unsigned int fd, int datasync)
 
 SYSCALL_DEFINE1(fsync, unsigned int, fd)
 {
-	if (!fsync_enabled)
-		return 0;
-
 	return do_fsync(fd, 0);
 }
 
 SYSCALL_DEFINE1(fdatasync, unsigned int, fd)
-{
-	if (!fsync_enabled)
-		return 0;
-
+{	
 	return do_fsync(fd, 1);
 }