When deleting a snapshot/subvolume, we need remove root ref/backref,
dir entries and update the dir inode, so we must reserve free space
for those operations.

Signed-off-by: Miao Xie <mi...@cn.fujitsu.com>
---
 fs/btrfs/ioctl.c |   21 +++++++++++++++++++--
 1 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 8046cfc..0b46081 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2064,6 +2064,8 @@ static noinline int btrfs_ioctl_snap_destroy(struct file 
*file,
        struct btrfs_root *dest = NULL;
        struct btrfs_ioctl_vol_args *vol_args;
        struct btrfs_trans_handle *trans;
+       struct btrfs_block_rsv block_rsv;
+       u64 qgroup_reserved;
        int namelen;
        int ret;
        int err = 0;
@@ -2153,12 +2155,23 @@ static noinline int btrfs_ioctl_snap_destroy(struct 
file *file,
        if (err)
                goto out_up_write;
 
+       btrfs_init_block_rsv(&block_rsv, BTRFS_BLOCK_RSV_TEMP);
+       /*
+        * One for dir inode, two for dir entries, two for root
+        * ref/backref.
+        */
+       err = btrfs_subvolume_reserve_metadata(root, &block_rsv,
+                                              5, &qgroup_reserved);
+       if (err)
+               goto out_up_write;
+
        trans = btrfs_start_transaction(root, 0);
        if (IS_ERR(trans)) {
                err = PTR_ERR(trans);
-               goto out_up_write;
+               goto out_release;
        }
-       trans->block_rsv = &root->fs_info->global_block_rsv;
+       trans->block_rsv = &block_rsv;
+       trans->bytes_reserved = block_rsv.size;
 
        ret = btrfs_unlink_subvol(trans, root, dir,
                                dest->root_key.objectid,
@@ -2188,10 +2201,14 @@ static noinline int btrfs_ioctl_snap_destroy(struct 
file *file,
                }
        }
 out_end_trans:
+       trans->block_rsv = NULL;
+       trans->bytes_reserved = 0;
        ret = btrfs_end_transaction(trans, root);
        if (ret && !err)
                err = ret;
        inode->i_flags |= S_DEAD;
+out_release:
+       btrfs_subvolume_release_metadata(root, &block_rsv, qgroup_reserved);
 out_up_write:
        up_write(&root->fs_info->subvol_sem);
 out_unlock:
-- 
1.6.5.2
--
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