btrfs: log, when replace, is canceled by the user

For debugging or administration purposes, we would want to know if and
when the user cancels the replace, to complement the existing messages
when dev-replace starts or finishes.
Signed-off-by: NAnand Jain <anand.jain@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
[ update changelog, fold fix for RCU warning from Nikolay ]
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/dev-replace.c

@@ -703,6 +703,7 @@ int btrfs_dev_replace_cancel(struct btrfs_fs_info *fs_info)
 {
 	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;
 	struct btrfs_device *tgt_device = NULL;
+	struct btrfs_device *src_device = NULL;
 	struct btrfs_trans_handle *trans;
 	struct btrfs_root *root = fs_info->tree_root;
 	int result;
@@ -724,6 +725,7 @@ int btrfs_dev_replace_cancel(struct btrfs_fs_info *fs_info)
 	case BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED:
 		result = BTRFS_IOCTL_DEV_REPLACE_RESULT_NO_ERROR;
 		tgt_device = dev_replace->tgtdev;
+		src_device = dev_replace->srcdev;
 		dev_replace->tgtdev = NULL;
 		dev_replace->srcdev = NULL;
 		break;
@@ -741,6 +743,12 @@ int btrfs_dev_replace_cancel(struct btrfs_fs_info *fs_info)
 	}
 	ret = btrfs_commit_transaction(trans);
 	WARN_ON(ret);
+
+	btrfs_info_in_rcu(fs_info,
+		"dev_replace from %s (devid %llu) to %s canceled",
+		btrfs_dev_name(src_device), src_device->devid,
+		btrfs_dev_name(tgt_device));
+
 	if (tgt_device)
 		btrfs_destroy_dev_replace_tgtdev(fs_info, tgt_device);