From: Josef Bacik <josef@toxicpanda.com>
Date: Fri, 12 Mar 2021 15:25:30 -0500
Subject: btrfs: do not panic in __add_reloc_root
Git-commit: 57a304cfd43b2b4a5b44b8f5dc026abb34183068
Patch-mainline: v5.13-rc1
References: bsc#1187833

If we have a duplicate entry for a reloc root then we could have fs
corruption that resulted in a double allocation.  Since this shouldn't
happen unless there is corruption, add an ASSERT(ret != -EEXIST) to all
of the callers of __add_reloc_root() to catch any logic mistakes for
developers, otherwise normal error handling will happen 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 |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -1350,7 +1350,7 @@ static int __must_check __add_reloc_root
 			      node->bytenr, &node->rb_node);
 	spin_unlock(&rc->reloc_root_tree.lock);
 	if (rb_node) {
-		btrfs_panic(fs_info, -EEXIST,
+		btrfs_err(fs_info,
 			    "Duplicate root found for start=%llu while inserting into relocation tree",
 			    node->bytenr);
 		kfree(node);
@@ -1562,6 +1562,7 @@ int btrfs_init_reloc_root(struct btrfs_t
 		return PTR_ERR(reloc_root);
 
 	ret = __add_reloc_root(reloc_root);
+	ASSERT(ret != -EEXIST);
 	if (ret)
 		return ret;
 	root->reloc_root = reloc_root;
@@ -4955,6 +4956,7 @@ int btrfs_recover_relocation(struct btrf
 		}
 
 		err = __add_reloc_root(reloc_root);
+		ASSERT(err != -EEXIST);
 		if (err) {
 			list_add_tail(&reloc_root->root_list, &reloc_roots);
 			btrfs_end_transaction(trans);
@@ -5176,6 +5178,7 @@ int btrfs_reloc_post_snapshot(struct btr
 		return PTR_ERR(reloc_root);
 
 	ret = __add_reloc_root(reloc_root);
+	ASSERT(ret != -EEXIST);
 	if (ret)
 		return ret;
 	new_root->reloc_root = reloc_root;