f2fs: avoid dead loop in f2fs_issue_checkpoint()

generic/082 reports a bug as below:

__schedule+0x332/0xf60
schedule+0x6f/0xf0
schedule_timeout+0x23b/0x2a0
wait_for_completion+0x8f/0x140
f2fs_issue_checkpoint+0xfe/0x1b0
f2fs_sync_fs+0x9d/0xb0
sync_filesystem+0x87/0xb0
dquot_load_quota_sb+0x41b/0x460
dquot_load_quota_inode+0xa5/0x130
dquot_quota_on+0x4b/0x60
f2fs_quota_on+0xe3/0x1b0
do_quotactl+0x483/0x700
__x64_sys_quotactl+0x15c/0x310
do_syscall_64+0x3f/0x90
entry_SYSCALL_64_after_hwframe+0x72/0xdc

The root casue is race case as below:

Thread A			Kworker			IRQ
- write()
: write data to quota.user file

				- writepages
				 - f2fs_submit_page_write
				  - __is_cp_guaranteed return false
				  - inc_page_count(F2FS_WB_DATA)
				 - submit_bio
- quotactl(Q_QUOTAON)
 - f2fs_quota_on
  - dquot_quota_on
   - dquot_load_quota_inode
    - vfs_setup_quota_inode
    : inode->i_flags |= S_NOQUOTA
							- f2fs_write_end_io
							 - __is_cp_guaranteed return true
							 - dec_page_count(F2FS_WB_CP_DATA)
    - dquot_load_quota_sb
     - f2fs_sync_fs
      - f2fs_issue_checkpoint
       - do_checkpoint
        - f2fs_wait_on_all_pages(F2FS_WB_CP_DATA)
        : loop due to F2FS_WB_CP_DATA count is negative

Calling filemap_fdatawrite() and filemap_fdatawait() to keep all data
clean before quota file setup.

Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Author: chaseyu

fs/f2fs/super.c

@@ -2923,15 +2923,26 @@ static int f2fs_quota_on(struct super_block *sb, int type, int format_id,
 		return -EBUSY;
 	}
 
+	if (path->dentry->d_sb != sb)
+		return -EXDEV;
+
 	err = f2fs_quota_sync(sb, type);
 	if (err)
 		return err;
 
-	err = dquot_quota_on(sb, type, format_id, path);
+	inode = d_inode(path->dentry);
+
+	err = filemap_fdatawrite(inode->i_mapping);
 	if (err)
 		return err;
 
-	inode = d_inode(path->dentry);
+	err = filemap_fdatawait(inode->i_mapping);
+	if (err)
+		return err;
+
+	err = dquot_quota_on(sb, type, format_id, path);
+	if (err)
+		return err;
 
 	inode_lock(inode);
 	F2FS_I(inode)->i_flags |= F2FS_NOATIME_FL | F2FS_IMMUTABLE_FL;