Btrfs: check to see if root_list is empty before adding it to dead roots

A user reported a panic when running with autodefrag and deleting snapshots.
This is because we could end up trying to add the root to the dead roots list
twice.  To fix this check to see if we are empty before adding ourselves to the
dead roots list.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index d58cce77fc6c..af1931a5960d 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -983,12 +983,12 @@ static noinline int commit_cowonly_roots(struct btrfs_trans_handle *trans,
  * a dirty root struct and adds it into the list of dead roots that need to
  * be deleted
  */
-int btrfs_add_dead_root(struct btrfs_root *root)
+void btrfs_add_dead_root(struct btrfs_root *root)
 {
         spin_lock(&root->fs_info->trans_lock);
-        list_add_tail(&root->root_list, &root->fs_info->dead_roots);
+        if (list_empty(&root->root_list))
+                list_add_tail(&root->root_list, &root->fs_info->dead_roots);
         spin_unlock(&root->fs_info->trans_lock);
-        return 0;
 }
 
 /*
@@ -1925,7 +1925,7 @@ int btrfs_clean_one_deleted_snapshot(struct btrfs_root *root)
         }
         root = list_first_entry(&fs_info->dead_roots,
                         struct btrfs_root, root_list);
-        list_del(&root->root_list);
+        list_del_init(&root->root_list);
         spin_unlock(&fs_info->trans_lock);
 
         pr_debug("btrfs: cleaner removing %llu\n",