btrfs: handle errors from select_reloc_root()

Currently select_reloc_root() doesn't return an error, but followup
patches will make it possible for it to return an error.  We do have
proper error recovery in do_relocation however, so handle the
possibility of select_reloc_root() having an error properly instead of
BUG_ON(!root).

I've also adjusted select_reloc_root() to return ERR_PTR(-ENOENT) if we
don't find a root, instead of NULL, to make the error case easier to
deal with.  I've replaced the BUG_ON(!root) with an ASSERT(0) for this
case as it indicates we messed up the backref walking code, but it could
also indicate corruption.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index e5fbc2c..146c7db 100644 (file)
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -2024,8 +2024,14 @@ struct btrfs_root *select_reloc_root(struct btrfs_trans_handle *trans,
                if (!next || next->level <= node->level)
                        break;
        }
-       if (!root)
-               return NULL;
+       if (!root) {
+               /*
+                * This can happen if there's fs corruption or if there's a bug
+                * in the backref lookup code.
+                */
+               ASSERT(0);
+               return ERR_PTR(-ENOENT);
+       }
 
        next = node;
        /* setup backref node path for btrfs_reloc_cow_block */
@@ -2196,7 +2202,10 @@ static int do_relocation(struct btrfs_trans_handle *trans,
 
                upper = edge->node[UPPER];
                root = select_reloc_root(trans, rc, upper, edges);
-               BUG_ON(!root);
+               if (IS_ERR(root)) {
+                       ret = PTR_ERR(root);
+                       goto next;
+               }
 
                if (upper->eb && !upper->locked) {
                        if (!lowest) {