Re: [syzbot] [btrfs?] general protection fault in write_all_supers

[Lizhi Xu]

if we have IGNOREDATACSUMS then don't need to backup csum root 

#syz test

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index a6f5441e62d1..415ad3b07032 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1679,7 +1679,6 @@ static void backup_super_roots(struct btrfs_fs_info *info)
 
 	if (!btrfs_fs_compat_ro(info, BLOCK_GROUP_TREE)) {
 		struct btrfs_root *extent_root = btrfs_extent_root(info, 0);
-		struct btrfs_root *csum_root = btrfs_csum_root(info, 0);
 
 		btrfs_set_backup_extent_root(root_backup,
 					     extent_root->node->start);
@@ -1688,11 +1687,15 @@ static void backup_super_roots(struct btrfs_fs_info *info)
 		btrfs_set_backup_extent_root_level(root_backup,
 					btrfs_header_level(extent_root->node));
 
-		btrfs_set_backup_csum_root(root_backup, csum_root->node->start);
-		btrfs_set_backup_csum_root_gen(root_backup,
-					       btrfs_header_generation(csum_root->node));
-		btrfs_set_backup_csum_root_level(root_backup,
-						 btrfs_header_level(csum_root->node));
+		if (!btrfs_test_opt(info, IGNOREDATACSUMS)) {
+			struct btrfs_root *csum_root = btrfs_csum_root(info, 0);
+
+			btrfs_set_backup_csum_root(root_backup, csum_root->node->start);
+			btrfs_set_backup_csum_root_gen(root_backup,
+						       btrfs_header_generation(csum_root->node));
+			btrfs_set_backup_csum_root_level(root_backup,
+							 btrfs_header_level(csum_root->node));
+		}
 	}
 
 	/*