f2fs: flush pending checkpoints when freezing super

This avoids -EINVAL when trying to freeze f2fs.

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

fs/f2fs/checkpoint.c

@@ -1893,15 +1893,27 @@ int f2fs_start_ckpt_thread(struct f2fs_sb_info *sbi)
 void f2fs_stop_ckpt_thread(struct f2fs_sb_info *sbi)
 {
 	struct ckpt_req_control *cprc = &sbi->cprc_info;
+	struct task_struct *ckpt_task;
 
-	if (cprc->f2fs_issue_ckpt) {
-		struct task_struct *ckpt_task = cprc->f2fs_issue_ckpt;
+	if (!cprc->f2fs_issue_ckpt)
+		return;
 
+	ckpt_task = cprc->f2fs_issue_ckpt;
 	cprc->f2fs_issue_ckpt = NULL;
 	kthread_stop(ckpt_task);
 
+	f2fs_flush_ckpt_thread(sbi);
+}
+
+void f2fs_flush_ckpt_thread(struct f2fs_sb_info *sbi)
+{
+	struct ckpt_req_control *cprc = &sbi->cprc_info;
+
 	flush_remained_ckpt_reqs(sbi, NULL);
-	}
+
+	/* Let's wait for the previous dispatched checkpoint. */
+	while (atomic_read(&cprc->queued_ckpt))
+		io_schedule_timeout(DEFAULT_IO_TIMEOUT);
 }
 
 void f2fs_init_ckpt_req_control(struct f2fs_sb_info *sbi)

fs/f2fs/f2fs.h

@@ -3711,6 +3711,7 @@ static inline bool f2fs_need_rand_seg(struct f2fs_sb_info *sbi)
  * checkpoint.c
  */
 void f2fs_stop_checkpoint(struct f2fs_sb_info *sbi, bool end_io);
+void f2fs_flush_ckpt_thread(struct f2fs_sb_info *sbi);
 struct page *f2fs_grab_meta_page(struct f2fs_sb_info *sbi, pgoff_t index);
 struct page *f2fs_get_meta_page(struct f2fs_sb_info *sbi, pgoff_t index);
 struct page *f2fs_get_meta_page_retry(struct f2fs_sb_info *sbi, pgoff_t index);

fs/f2fs/super.c

@@ -1671,9 +1671,8 @@ static int f2fs_freeze(struct super_block *sb)
 	if (is_sbi_flag_set(F2FS_SB(sb), SBI_IS_DIRTY))
 		return -EINVAL;
 
-	/* ensure no checkpoint required */
-	if (!llist_empty(&F2FS_SB(sb)->cprc_info.issue_list))
-		return -EINVAL;
+	/* Let's flush checkpoints and stop the thread. */
+	f2fs_flush_ckpt_thread(F2FS_SB(sb));
 
 	/* to avoid deadlock on f2fs_evict_inode->SB_FREEZE_FS */
 	set_sbi_flag(F2FS_SB(sb), SBI_IS_FREEZING);