f2fs: introduce cp_lock to protect updating of ckpt_flags

This patch introduces spinlock to protect updating process of ckpt_flags
field in struct f2fs_checkpoint, it avoids incorrectly updating in race
condition.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
[Jaegeuk Kim: add __is_set_ckpt_flags likewise __set_ckpt_flags]
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 9649b79..95986a9 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -736,7 +736,7 @@
 	 * clean checkpoint again.
 	 */
 	if (is_sbi_flag_set(sbi, SBI_IS_DIRTY) ||
-			!is_set_ckpt_flags(F2FS_CKPT(sbi), CP_UMOUNT_FLAG)) {
+			!is_set_ckpt_flags(sbi, CP_UMOUNT_FLAG)) {
 		struct cp_control cpc = {
 			.reason = CP_UMOUNT,
 		};
@@ -1478,6 +1478,7 @@
 	mutex_init(&sbi->umount_mutex);
 	mutex_init(&sbi->wio_mutex[NODE]);
 	mutex_init(&sbi->wio_mutex[DATA]);
+	spin_lock_init(&sbi->cp_lock);
 
 #ifdef CONFIG_F2FS_FS_ENCRYPTION
 	memcpy(sbi->key_prefix, F2FS_KEY_DESC_PREFIX,
@@ -1819,7 +1820,7 @@
 		 * previous checkpoint was not done by clean system shutdown.
 		 */
 		if (bdev_read_only(sb->s_bdev) &&
-				!is_set_ckpt_flags(sbi->ckpt, CP_UMOUNT_FLAG)) {
+				!is_set_ckpt_flags(sbi, CP_UMOUNT_FLAG)) {
 			err = -EROFS;
 			goto free_kobj;
 		}