f2fs: guarantee to write dirty data when enabling checkpoint back

We must flush all the dirty data when enabling checkpoint back. Let's guarantee
that first by adding a retry logic on sync_inodes_sb(). In addition to that,
this patch adds to flush data in fsync when checkpoint is disabled, which can
mitigate the sync_inodes_sb() failures in advance.
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/file.c

@@ -263,8 +263,7 @@ static int f2fs_do_sync_file(struct file *file, loff_t start, loff_t end,
 	};
 	unsigned int seq_id = 0;
 
-	if (unlikely(f2fs_readonly(inode->i_sb) ||
-				is_sbi_flag_set(sbi, SBI_CP_DISABLED)))
+	if (unlikely(f2fs_readonly(inode->i_sb)))
 		return 0;
 
 	trace_f2fs_sync_file_enter(inode);
@@ -278,7 +277,7 @@ static int f2fs_do_sync_file(struct file *file, loff_t start, loff_t end,
 	ret = file_write_and_wait_range(file, start, end);
 	clear_inode_flag(inode, FI_NEED_IPU);
 
-	if (ret) {
+	if (ret || is_sbi_flag_set(sbi, SBI_CP_DISABLED)) {
 		trace_f2fs_sync_file_exit(inode, cp_reason, datasync, ret);
 		return ret;
 	}

fs/f2fs/super.c

@@ -2083,8 +2083,17 @@ static int f2fs_disable_checkpoint(struct f2fs_sb_info *sbi)
 
 static void f2fs_enable_checkpoint(struct f2fs_sb_info *sbi)
 {
+	int retry = DEFAULT_RETRY_IO_COUNT;
+
 	/* we should flush all the data to keep data consistency */
+	do {
 		sync_inodes_sb(sbi->sb);
+		cond_resched();
+		congestion_wait(BLK_RW_ASYNC, DEFAULT_IO_TIMEOUT);
+	} while (get_pages(sbi, F2FS_DIRTY_DATA) && retry--);
+
+	if (unlikely(retry < 0))
+		f2fs_warn(sbi, "checkpoint=enable has some unwritten data.");
 
 	down_write(&sbi->gc_lock);
 	f2fs_dirty_to_prefree(sbi);