[PATCH v2 06/42] btrfs: handle errors from select_reloc_root()

[Josef Bacik <josef@toxicpanda.com>]

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(ret != -ENOENT), as this indicates we messed up the backref
walking code, but could indicate corruption so we do not want to have a
BUG_ON() here.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/relocation.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 3a5e89c82fa5..89e9253846cc 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -2037,7 +2037,7 @@ struct btrfs_root *select_reloc_root(struct btrfs_trans_handle *trans,
 			break;
 	}
 	if (!root)
-		return NULL;
+		return ERR_PTR(-ENOENT);
 
 	next = node;
 	/* setup backref node path for btrfs_reloc_cow_block */
@@ -2209,7 +2209,18 @@ 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)) {
+			err = PTR_ERR(root);
+
+			/*
+			 * This can happen if there's fs corruption, but if we
+			 * have ASSERT()'s on then we're developers and we
+			 * likely made a logic mistake in the backref code, so
+			 * check for this error condition.
+			 */
+			ASSERT(err != -ENOENT);
+			goto next;
+		}
 
 		if (upper->eb && !upper->locked) {
 			if (!lowest) {
-- 
2.26.2