[PATCH] Btrfs: set dead flag on the right root when destroying snapshot

[Filipe David Borba Manana <fdmanana@gmail.com>]

We were setting the BTRFS_ROOT_SUBVOL_DEAD flag on the root of the
parent of our target snapshot, instead of setting it in the target
snapshot's root.

This is easy to observe by running the following scenario:

    mkfs.btrfs -f /dev/sdd
    mount /dev/sdd /mnt

    btrfs subvolume create /mnt/first_subvol
    btrfs subvolume snapshot -r /mnt /mnt/mysnap1

    btrfs subvolume delete /mnt/first_subvol
    btrfs subvolume snapshot -r /mnt /mnt/mysnap2

    btrfs send -p /mnt/mysnap1 /mnt/mysnap2 -f /tmp/send.data

The send command failed because the send ioctl returned -EPERM.
A test case for xfstests follows.

Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
---
 fs/btrfs/ioctl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 362720a..482cad5 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2314,7 +2314,7 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
 	spin_lock(&dest->root_item_lock);
 	root_flags = btrfs_root_flags(&root->root_item);
 	if (root->send_in_progress == 0) {
-		btrfs_set_root_flags(&root->root_item,
+		btrfs_set_root_flags(&dest->root_item,
 				root_flags | BTRFS_ROOT_SUBVOL_DEAD);
 		spin_unlock(&dest->root_item_lock);
 	} else {
@@ -2417,7 +2417,7 @@ out_unlock:
 	if (err) {
 		spin_lock(&dest->root_item_lock);
 		root_flags = btrfs_root_flags(&root->root_item);
-		btrfs_set_root_flags(&root->root_item,
+		btrfs_set_root_flags(&dest->root_item,
 				root_flags & ~BTRFS_ROOT_SUBVOL_DEAD);
 		spin_unlock(&dest->root_item_lock);
 	}
-- 
1.9.1