From: Josef Bacik <josef@toxicpanda.com>
Date: Fri, 12 Mar 2021 15:25:32 -0500
Subject: btrfs: handle extent corruption with select_one_root properly
Git-commit: 8717cf440db670ba87596d8f5f6660d2a94f4401
Patch-mainline: v5.13-rc1
References: bsc#1187833

In corruption cases we could have paths from a block up to no root at
all, and thus we'll BUG_ON(!root) in select_one_root.  Handle this by
adding an ASSERT() for developers, and returning an error for normal
users.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Acked-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/relocation.c |   19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -2893,7 +2893,13 @@ struct btrfs_root *select_one_root(struc
 		cond_resched();
 		next = walk_up_backref(next, edges, &index);
 		root = next->root;
-		BUG_ON(!root);
+
+		/*
+		 * This can occur if we have incomplete extent refs leading all
+		 * the way up a particular path, in this case return -EUCLEAN.
+		 */
+		if (!root)
+			return ERR_PTR(-EUCLEAN);
 
 		/* no other choice for non-references counted tree */
 		if (!test_bit(BTRFS_ROOT_REF_COWS, &root->state))
@@ -3308,8 +3314,15 @@ static int relocate_tree_block(struct bt
 
 	BUG_ON(node->processed);
 	root = select_one_root(node);
-	if (root == ERR_PTR(-ENOENT)) {
-		update_processed_blocks(rc, node);
+	if (IS_ERR(root)) {
+		ret = PTR_ERR(root);
+
+		/* See explanation in select_one_root for the -EUCLEAN case. */
+		ASSERT(ret == -ENOENT);
+		if (ret == -ENOENT) {
+			ret = 0;
+			update_processed_blocks(rc, node);
+		}
 		goto out;
 	}