f2fs: stop gc/discard thread after fs shutdown

Once filesystem shuts down, daemons like gc/discard thread should be
aware of it, and do exit, in addtion, drop all cached pending discard
commands and turn off real-time discard mode.
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -2726,6 +2726,7 @@ void invalidate_blocks(struct f2fs_sb_info *sbi, block_t addr);
 bool is_checkpointed_data(struct f2fs_sb_info *sbi, block_t blkaddr);
 void init_discard_policy(struct discard_policy *dpolicy, int discard_type,
 						unsigned int granularity);
+void drop_discard_cmd(struct f2fs_sb_info *sbi);
 void stop_discard_thread(struct f2fs_sb_info *sbi);
 bool f2fs_wait_discard_bios(struct f2fs_sb_info *sbi);
 void clear_prefree_segments(struct f2fs_sb_info *sbi, struct cp_control *cpc);

fs/f2fs/file.c

@@ -1866,6 +1866,13 @@ static int f2fs_ioc_shutdown(struct file *filp, unsigned long arg)
 		ret = -EINVAL;
 		goto out;
 	}
+
+	stop_gc_thread(sbi);
+	stop_discard_thread(sbi);
+
+	drop_discard_cmd(sbi);
+	clear_opt(sbi, DISCARD);
+
 	f2fs_update_time(sbi, REQ_TIME);
 out:
 	mnt_drop_write_file(filp);

fs/f2fs/segment.c

@@ -1263,6 +1263,11 @@ static bool __drop_discard_cmd(struct f2fs_sb_info *sbi)
 	return dropped;
 }
 
+void drop_discard_cmd(struct f2fs_sb_info *sbi)
+{
+	__drop_discard_cmd(sbi);
+}
+
 static unsigned int __wait_one_discard_bio(struct f2fs_sb_info *sbi,
 							struct discard_cmd *dc)
 {