f2fs: fix error path of f2fs_remount()

In error path of f2fs_remount(), it missed to restart/stop kernel thread
or enable/disable checkpoint, then mount option status may not be
consistent with real condition of filesystem, so let's reorder remount
flow a bit as below and do recovery correctly in error path:

1) handle gc thread
2) handle ckpt thread
3) handle flush thread
4) handle checkpoint disabling
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/super.c

@@ -1927,8 +1927,9 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
 	struct f2fs_mount_info org_mount_opt;
 	unsigned long old_sb_flags;
 	int err;
-	bool need_restart_gc = false;
-	bool need_stop_gc = false;
+	bool need_restart_gc = false, need_stop_gc = false;
+	bool need_restart_ckpt = false, need_stop_ckpt = false;
+	bool need_restart_flush = false, need_stop_flush = false;
 	bool no_extent_cache = !test_opt(sbi, EXTENT_CACHE);
 	bool disable_checkpoint = test_opt(sbi, DISABLE_CHECKPOINT);
 	bool no_io_align = !F2FS_IO_ALIGNED(sbi);
@@ -2059,19 +2060,10 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
 		clear_sbi_flag(sbi, SBI_IS_CLOSE);
 	}
 
-	if (checkpoint_changed) {
-		if (test_opt(sbi, DISABLE_CHECKPOINT)) {
-			err = f2fs_disable_checkpoint(sbi);
-			if (err)
-				goto restore_gc;
-		} else {
-			f2fs_enable_checkpoint(sbi);
-		}
-	}
-
 	if ((*flags & SB_RDONLY) || test_opt(sbi, DISABLE_CHECKPOINT) ||
 			!test_opt(sbi, MERGE_CHECKPOINT)) {
 		f2fs_stop_ckpt_thread(sbi);
+		need_restart_ckpt = true;
 	} else {
 		err = f2fs_start_ckpt_thread(sbi);
 		if (err) {
@@ -2080,6 +2072,7 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
 			    err);
 			goto restore_gc;
 		}
+		need_stop_ckpt = true;
 	}
 
 	/*
@@ -2089,11 +2082,24 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
 	if ((*flags & SB_RDONLY) || !test_opt(sbi, FLUSH_MERGE)) {
 		clear_opt(sbi, FLUSH_MERGE);
 		f2fs_destroy_flush_cmd_control(sbi, false);
+		need_restart_flush = true;
 	} else {
 		err = f2fs_create_flush_cmd_control(sbi);
 		if (err)
-			goto restore_gc;
+			goto restore_ckpt;
+		need_stop_flush = true;
 	}
+
+	if (checkpoint_changed) {
+		if (test_opt(sbi, DISABLE_CHECKPOINT)) {
+			err = f2fs_disable_checkpoint(sbi);
+			if (err)
+				goto restore_flush;
+		} else {
+			f2fs_enable_checkpoint(sbi);
+		}
+	}
+
 skip:
 #ifdef CONFIG_QUOTA
 	/* Release old quota file names */
@@ -2108,6 +2114,21 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
 	adjust_unusable_cap_perc(sbi);
 	*flags = (*flags & ~SB_LAZYTIME) | (sb->s_flags & SB_LAZYTIME);
 	return 0;
+restore_flush:
+	if (need_restart_flush) {
+		if (f2fs_create_flush_cmd_control(sbi))
+			f2fs_warn(sbi, "background flush thread has stopped");
+	} else if (need_stop_flush) {
+		clear_opt(sbi, FLUSH_MERGE);
+		f2fs_destroy_flush_cmd_control(sbi, false);
+	}
+restore_ckpt:
+	if (need_restart_ckpt) {
+		if (f2fs_start_ckpt_thread(sbi))
+			f2fs_warn(sbi, "background ckpt thread has stopped");
+	} else if (need_stop_ckpt) {
+		f2fs_stop_ckpt_thread(sbi);
+	}
 restore_gc:
 	if (need_restart_gc) {
 		if (f2fs_start_gc_thread(sbi))