f2fs: avoid wrong decrypted data from disk

1. Create a file in an encrypted directory
2. Do GC & drop caches
3. Read stale data before its bio for metapage was not issued yet

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -3195,10 +3195,14 @@ void f2fs_wait_on_page_writeback(struct page *page,
 	}
 }
 
-void f2fs_wait_on_block_writeback(struct f2fs_sb_info *sbi, block_t blkaddr)
+void f2fs_wait_on_block_writeback(struct inode *inode, block_t blkaddr)
 {
+	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
 	struct page *cpage;
 
+	if (!f2fs_post_read_required(inode))
+		return;
+
 	if (!is_valid_data_blkaddr(sbi, blkaddr))
 		return;